Yet there are a couple of problems with the OneSteps. First, most models were very basic, plasticky, fixed-focus cameras, not offering much versatility. The second problem is that their frame-counting mechanism locks the shutter after 10 shots. If you’re shooting multiple exposures onto each frame, at some point you’ll need to remove the film pack in a dark room to re-set the counter, which is inconvenient.

Polaroid’s SX-70 models were much more sophisticated than the OneSteps. They featured a compact, collapsible body, a good-quality glass lens, and true SLR focusing all the way down to 10″. However they’re a bit tricky to disassemble, so the “kill switch” mod I described earlier would be rather complicated to try on an SX-70.

An SX-70—even a thrashed one like my white model 2—is a sleeker, nicer camera than any of Polaroid’s OneStep models.

But Flickr user amalia chimera called my attention to a YouTube video by her friend Brian (whose demonstration of double-exposures on a Spectra camera I had previously linked to). In a second video he shows a technique for fooling SX-70 cameras to make double-exposures possible.

Basically, the trick is this: An SX-70 has an interlock so that if the film door is open, the shutter and eject motor won’t operate. However by pressing the door-sensor lever with a narrow tool, you can take a shot even with the door open. Because the feed rollers are disengaged then, the print does not get ejected and developed. You can nudge the print back into the pack and make a second exposure.

An SX-70 does require an exposure adjustment to use 600 film. But that’s a minor problem. And I would much rather shoot with an SX-70 than a cheesy OneStep, so Brian’s technique really excited me. Plus, no permanent surgery to the camera was needed. So here’s a few refinements and additions to what Brian’s video shows.

Start by cutting a bit of kitchen match or barbecue skewer so that it’s exactly 41mm long. (I’ll explain the reason for the piece of tape later.)

When you open the camera’s film door, you will see a small, dull gray piece of folded metal on the left edge—directly below the plastic ribbon cable. There is a peg on the film door which rises up behind this when the camera is closed; it lifts a small black plastic lever. This is the switch we need to “fool” with our special tool.

By using a stick exactly 41mm long, we can brace it against the film door’s light baffle and keep the switch pressed upwards.

With the switch overridden, you can take your first exposure without ejecting the print. Because you might walk around in full daylight for some time before finding the right subject, there’s a risk of light leaking into the front edge of the film pack. If you’d prefer to avoid this, you can wrap the front of the camera with a shroud of black cloth, paper, etc.

Cloth shroud held in place with rubber band

One of the many clever features of the SX-70 is that any adjustment made to the lighter-darker dial would be reset to zero whenever the camera was folded. However you will probably find your double exposures will look too washed out if you don’t set the dial towards the darker end of the scale before shooting. It’s a slight annoyance that you have to remember to do this every time you open the camera.

Remember to turn the exposure dial towards the black!

When you take your first image, about 1/8″ of the print edge is shoved out of the film pack. Ordinarily this would feed it into the rollers, which spread the chemical goo inside the print and start development. But we’ve prevented this.

It’s extremely important that you shove the print edge as far back into the film pack as possible, behind its flexible plastic light shield, until no more white is visible. Otherwise you run the risk of the camera ejecting two prints at once, spoiling both. But the wood stick we cut turns out to be a handy tool for nudging the print back into place.

Try to go somewhere in dim light before shoving the print edge back into the pack, since this is the stage where you’re most likely to flash the bottom of the image with light leaks. But I’ve become kind of fond of the “row of teeth” light effect you sometimes get from this (seen in the sample image below).

Now close the film door and shoot the second image. As I noted last time, any bright area in your subject tends to blow out whatever detail might have appeared in the other image. Experiment with leaving lots of dark, blank areas in the frame to give the clearest “double-iness” to the final photo. The SX-70’s extra-close focusing can help you isolate simple and uncluttered subjects.

A happy discovery was that an SX-70 does not lock the shutter after 10 exposures (at least, my Model 2 doesn’t). The frame counter goes down to 0 shots and stays there; but you can keep on clicking until all the prints in the pack are used up. But it’s up to you to keep track of the correct count, of course.

Remember that piece of tape wrapped around the stick? Here’s one more tip: You can always keep your double-exposure tool handy by taping it under the SX-70 viewfinder hood. There’s enough space at the back end to allow the viewfinder to fold normally; and the stick won’t get lost this way.

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If you need an impromptu light table, just open a blank document/browser window on your laptop (or LCD desktop monitor). Sweet!

In today’s dark times waiting for the End of Polaroid, pack film may be our one remaining bright note. Because Polaroid’s older patents have expired, Fujifilm was able to introduce a line of instant films that are drop-in replacements, fitting all the same cameras and backs. And better yet, they’re cheaper than most Polaroid options.

One of Polaroid’s peel-apart film types, number 669, is cherished for its odd color tonality and workability for emulsion-lift techniques—regrettably there does not seem to be any direct Fuji replacement for this. But otherwise, my early tests with Fuji’s FP-100C color packfilm seem promising. I have heard much praise for their B&W emulsions too, but have not tried them myself.

We can’t know how long Fuji will continue making these films, of course. But my speculation is that with their setup costs already paid and their only competitor leaving the market, Fuji’s packfilm will be the one remaining “Polaroid” material available in the coming years.

As I’ve complained before, most of the amateur-grade cameras sold by Polaroid itself were rather uninspired. Most featured slow, pedestrian-quality lenses and have no option for manual exposure control. Polaroid did make a handful of “professional” manual-exposure models like the 180 & 195; Or the 600SE (basically an adapted Mamiya press camera). But the relative scarcity of these models keeps their prices high on the used market even today.

However, the company produced millions of consumer folding models—all of which used essentially the same standardized film back and bellows assembly. Just start looking around at yard sales and camera swaps, and you’ll find numerous 100-, 200-, 300-, and 400-series cameras, generally at giveaway prices.

Polaroid sold many variations on this basic design; here a Model 104

Considering their ubiquity and low value, there’s no need to feel guilty about cannibalizing one for other purposes. Other possible lens-shutter combinations can be adapted to replace Polaroid’s original; all that’s needed is an image circle covering the 120mm print diagonal (or just close to it, if you enjoy some vignetting). People have even adapted Holga and Diana lens/shutter assemblies to work!

But to me, the main reason to make such a conversion is to gain full manual exposure control with true f/stop and shutter-speed settings; and perhaps to use a focal length never available from Polaroid’s own offerings.

In my stash of random optics, I had a nice 1961 Schneider Angulon lens in a Compur shutter (scored cheaply at an estate sale once). Its 90mm focal length would yield intriguing semi-wide coverage on the packfilm format (about equivalent to a 32mm lens on 135 film).

The Angulon’s f/6.8 maximum aperture doesn’t sound too exciting; but this still is an improvement on Polaroid’s typical f/8.8 lens. A bit of research told me that the 90mm Angulon formula (not “Super”) covers 4×5″ film—so on the smaller Polaroid format, there was even room for some shifts and swings if I wanted them!

Thus I resolved to build a home-hacked “field camera” based on an unused Polaroid model 420 I had been given. (Thanks Ralph!)

I won’t repeat the excellent disassembly photos on this Italian blog, which apply to most accordion-style Polaroid models. But my first step was to remove the whole lens and shutter assembly. Because of the different focal length of my new lens, the original viewfinder and rangefinder became useless too, so I removed those as well.

The original lens on these cameras has a focal length of 114mm. To focus at infinity with a 90mm lens, I would not be able to extend the old lensboard and struts to their original locked position. So after a bit of hacking I extracted most of the strut parts too.

The front rim of the bellows includes a metal piece, whose opening needed to be carefully enlarged to accommodate the diameter of the Schneider lens.

This camera was definitely a quick experiment. So to keep construction simple, I didn’t attempt to engineer any fancy collapsing lens mechanism myself. Instead my scheme was just to hot-glue a slab of plywood to the bottom of the camera; then mount the lens on a sliding standard made from a stiff ‘L’ of scrap aluminum. This does mean that the completed camera is a bit of an armful to carry around, though!

The height of the lens hole aligns with the center of the bellows; there is is a smaller hole at its perimeter, for a peg on the shutter which keeps the lens from spinning. I slotted the bottom of the standard so that when the camera was in the vertical orientation (e.g. shooting a building) I could shift the lens upwards for perspective control.

As turns out, I was too conservative with my +/- 23mm of shift: The lens has enough coverage that I should have gone for more. I made it possible to pivot the aluminum standard, too, hoping this would be useful for focus control; but in my experience, the effect of this is pretty subtle, given the generous depth of field of the Angulon and the small print size. But if you were using a longer, faster lens, it might be useful.

The aluminum lens standard is simply glued to the front of the bellows with a generous bead of black silicone sealant (sold as auto gasket material). I used clothespins to hold those parts together until the silicone cured (with my nice lens removed, of course!).

The plywood is slotted for focus travel, with a wingnut on the bolt allowing fingertip loosening and tightening. The bottom of the plywood also includes my favorite homebrew “tripod socket”: A 1/4″-20 nut epoxied into a shallow hole.

The next step was to calibrate the focusing scale for different distances. To do this, I cannibalized an empty film pack and made a ground-glass back with it. The frosted surface is just sandpapered plexiglass; this needs to be glued tight inside the plastic front of the film pack, frosted side forward, to be in the correct film plane. (The metal pack parts are discarded.)

With that held into the camera and the back swung open, I measured off known subject distances and then used a magnifier to find the best points of focus on the groundglass. It turns out that the amount of lens movement needed to focus from infinity to 4 feet is surprisingly small. But conveniently, the extra bellows extension available permits focusing down to 2 feet or closer. (You can see where I’ve added marker lines on the plywood, corresponding to several measured subject distances.)

Unfortunately a Polaroid film pack doesn’t have a dark slide; so you can only use the groundglass to set up the camera, not as a focus aid for each shot. Fortunately focus turns out to be fairly non-critical even wide open at f/6.8. Guessing at the subject distance has turned out to be an entirely adequate method of focusing this beast.

There were a few finishing touches to the camera: I screwed a metal accessory shoe into the plastic body, salvaged from another camera carcass; it’s used for an auxiliary viewfinder approximating the correct semi-wide lens coverage. (No, that is not a VIOOH, you Leica geeks; just a cheap Japanese copy.) That finder actually has the wrong aspect ratio and inaccurate parallax compensation—but hey it’s better than nothing.

I also added a nice lens shade via a Series VI adapter; and trimmed the corners of the plywood so they’d be less likely to snag in the oversized beach bag I use to lug this camera around.

I must confess that the “tilt-shift” aspect of this project did not turn out to be as useful as I’d hoped. So it’s a bit hard to justify the bulk of the completed camera. Yet it’s a delight to be able to use an honest-to-god handheld light meter and conventional exposure settings with Polaroid materials. Here’s a sample from my trial of Fujifilm’s FP-100C packfilm. (It seems Fuji comes through with the greens again!)

I’ve nicknamed my Frankenstein creation “the Anguloid.” If you’re interested in more samples, check out my photos on Flickr tagged with that.

As I understand it, the factory production lines for Polaroid film have actually stopped; what’s left is a few months’ supply still in the distribution pipeline. So I’ve been buying up Polaroid 600 packs whenever I come across them. (The best prices I’ve found are at Office Depot online; and locally—brrrr—at Walmart.)

But to stretch those last remaining shots, what better idea than to expose each frame more than once?

Most of the peel-apart packfilm cameras allow double exposures easily; and there is a known technique to trick Spectra cameras into shooting them. But for 600 film cameras, the only method I have learned about seemed complex and inconvenient.

But today I have a nifty camera mod which permits double exposures on 600 film—an inspired idea by my friend Allison Stanley. She owns a well-used Polaroid One600 camera, which sometimes failed to eject prints correctly. Appreciating the quirky beauty of her overlapping exposures, she suggested wiring in a “kill switch” to disable the print-eject motor at will.

I thought that idea was pure genius, and immediately wanted to try it out. It turns out that there’s a slight complication: All the 600 cameras I experimented with use the feed motor to recock the shutter too. But still, after adding the switch, a workable technique for 600-film double exposures does become possible.

Opening Up the Camera

The Polaroid One Step shown here is a typical 600 film model—easy to find for a few dollars at the thrift store etc. And this gray body-style with its flip-up flash is particularly easy to open: Its plastic shell simply snaps together. Let’s look.

Start by taking the flip-up flash and holding at about a 45-degree angle as shown. At this angle, it is possible to gently flex the side ears of the flash outwards and pop them free from the the camera body.

Lay the flash back on the top of the camera, out of the way as you remove the front panel. (But try not to put too much strain on that delicate ribbon cable as you go through the following steps.)

The front of the camera simply snaps into place; carefully insert a prying tool at the points shown by my knife and the red arrow; then ease the camera faceplate free. (The shutter button parts will fall out loose, so work over a towel or a tray so nothing gets lost.)

Here’s the opened camera, with the shutter-button assembly at left and the removed front panel at right.

Locate the ribbon cable which connects to the motor at the front of the camera. The conductors I’m pointing to are the ones that provide electricity to the motor. All we need to do is to cut through one wire and route it through an external switch, and the camera’s film-eject motor can be disabled as desired.

One flaw of that gray One Step above is that its electronic flash fires with every shot. Especially for double-exposures, I preferred not to risk washed-out colors by always using flash; instead I made the kill-switch mod to a vintage “rainbow” OneStep600 instead. But its disassembly needs a few extra steps. If you want to modify one of these, see the details here, then return for the other steps below.

Make the Hack

With small scissors cut through one of the conductors of the ribbon cable (the left side gives you more length of wire to work with). Then slice the clear plastic between conductors so you can pull the free cut ends outwards.

Prepare a small switch by soldering about 3 inches of wire to it. The type of switch isn’t important; but for ease of remembering I’d suggest orienting it so the contacts close when the switch is moved towards the front of the camera.

Drill a small hole in the side of the camera, into the hollow space under the photocell assembly. Thread the switch wires through this hole. Be sure to locate the hole far enough back so that the camera’s front panel can be replaced without interfering.

You could do a neater job than I did by mounting the switch inside the camera body; but I actually preferred mounting it in a sideways orientation where it would be less likely to get snagged and flipped accidentally. I glued the switch into place with hot-melt glue, adding an extra blob on the bottom to cover and insulate the solder tabs.

Cut back any excess length of the two wires, and solder their ends to the cut motor ribbon cable. The ribbon seems to be tinned already, so I found soldering to it surprisingly easy; but you do need to avoid jiggling the wires while the molten solder cools. (Forceps, etc. could be useful here to hold wires steady.)

That’s it!

Now it’s time to put the camera’s front back on. Be sure the lighter/darker control is centered so it will engage with the internal slider properly. I think it’s easiest to reinstall the shutter button parts by tucking them into the recess on the camera’s front, then sliding all the parts back into place as a unit:

Re-attach the flash pivots (again holding it at a 45° angle) and the camera is ready to use.

Using the Modded Camera

Okay, we’ll assume you’ve wired the switch so that when flipped forwards, the contacts are closed. In this position the camera operates exactly as originally.

Keep the switch “on,” and load a fresh film pack. When you close the door, the black cover sheet should eject. (If it doesn’t, something is wrong: Re-check your work.)

Remember, after every exposure the motor needs to run sometime, to re-cock the shutter and prepare for the next shot. But the switch allows us to delay that, and not have the print spit out immediately.

So the technique for double exposures is this:

• Flip the switch backwards, and make your first exposure (shutter fires, but print does not eject). I’d suggest that you slide the lighter-darker control all the way to darker for your first tests.

• Drop the film door open; then flip the switch forward (the motor immediately runs; but the rollers are disengaged so the print stays inside the pack)

• The front edge of the print (or as shown here, two prints) is pushed out of the pack slightly. Carefully push these front edges back into the film pack, as far as you are able.

• Close the door, leave the switch forward, and make your second exposure (print ejects normally).

• A third exposure (etc.) is possible by repeating the same cycle:

Switch off/shoot/drop door/switch on/tuck print into pack/close door.

There’s a couple things to note about this method. One is that pushing the front edge of the print back into the pack in daylight can leak light into the pack: This gives the funny “row of teeth” pattern seen at the bottom of this shot:

You can minimize this, by delaying the door-drop maneuver until you can move into dim light (or, push the print edge back into the pack by feel, with a jacket etc. thrown over the camera). But I’ve actually grown rather fond of this quirk.

The other issue is a general one for double-exposures: You can only add light, not subtract it. Any brightly-lit area of your subject tends to override the image in the other exposure. It’s mainly in the darker areas of the scene where you’ll see the double-ness of the exposure. So try to include sufficient dark, blank areas in your shots. And stick to simple, bold subjects until you get the hang of how images combine.

These are strange days, when the cost of a complete Polaroid camera is trivial compared to the preciousness of each exposure. Yet the freedom to cut up and re-jigger old cameras is liberating, too. And the magical serendipity of Polaroid doubles seems like a fine way to celebrate our farewell to this unique and irreplaceable medium.

Important Update: with most 600 cameras, making double-exposures will confuse the frame counter. After making 10 exposures (not after ejecting 10 prints) the shutter button will lock.

The slightly-inconvenient cure is this: grab a spare black film-pack cover sheet and go into a dark room. Open the camera, remove the film pack entirely, and slip the black sheet back into the top of the film pack. (Orient the little dangly plastic tag towards the cut-away corner of the pack.) Close the film door, and allow the camera to spit out the black sheet again (flip on the kill-switch if needed). The frame counter will be reset and you may continue taking pictures.

Aside from a few price-gougers on eBay, there are no supplies remaining of the Time-Zero film packs created for the SX-70 cameras. However, there are many descriptions on the web of how to adapt a Polaroid SX-70 camera to use 600 film packs—even Polaroid has one.

The basic problem is that the original Time Zero film packs for the SX-70 had a speed of ISO 75; while 600 film has a speed of… well, 600. There are a couple of ways to solve this, and I won’t repeat all the information available elsewhere.

I wanted a solution that left the camera in unmodified, original condition, and didn’t rely on the “lighter/darker” dial for adjustment. The simplest answer is to add a 2-stop neutral-density filter over the lens. (Admittedly, this makes the viewfinder image rather dim.)

Originally I had high hopes for holding a regular Hoya screw-in polarizer in front of the lens: This cuts out about two stops, plus would have sometimes helped deepen colors by rotating it to different angles.

But it turned out to be a real fumble to hold the polarizer in the correct place; and worse, the image seemed a bit washed-out and greenish.

Flexible gelatin filters are a better choice: They can be taped permanently in place while allowing the camera to collapse normally. So I wanted to report success in adapting my SX-70 using filters taken from a swatchbook of Roscolux theatrical gels.

You only need about 30mm square to cover an SX-70 lens. Perhaps some friendly theater tech will let you snip out what you need from their samples or scraps. I got my swatchbook by requesting it from a form on the Rosco website—but perhaps too many photographers were abusing this, because the page has vanished now (I blame Strobist readers!)

Roscolux filter samples have handy light-transmission info included right in the swatchbook. So it was an easy choice to start with #98 “Medium Grey,” which claimed 25% light transmission (that is exactly two stops). I found the exposure was almost perfect—perhaps just a shade light on my camera. However there was a slight greenish tinge to the image which bothered me a bit.

I tried sandwiching the gray filter with #3318, a pale magenta “1/8 Minusgreen.” That worked great, but still gave a slightly bluish color palette. Finally I tried the #98 gray plus #05, “Rose Tint.” This seemed like the best combination overall—slightly warmer grays but still neutral. Having said that, the color casts were pretty subtle and you might be happy with any of them.

Polaroid 600 film shot in SX-70

The other issue with fitting 600 packs into an SX-70 is that there are four little plastic nubs on the bottom of the pack whose purpose is to stop you from sliding them into the “wrong” camera. It’s possible to use a stiff card to slip those over the obstructions in the SX-70’s film compartment; or even to force the pack into place by tipping it in at an angle.

But it’s no real problem to shave the nubs away with a sharp blade. According to Polaroid, it’s only the two middle nubs which hang up on the opening to the film chamber.

With these two mods, you can take that sleek SX-70, in all its folding, close-focusing grooviness, and put it back to use again!

[See another Polaroid project: the Pack-film Pinhole]

________

UPDATE: June 20, 2008

Thanks to Megan, commenting below, for noting that you can buy the Roscolux sample book for $4—good tip!

Contrary to the instructions widely posted on the Internet, my original silver SX-70 did not have a neutral density filter over its photocell; hence I needed a 2-stop filter over its lens for proper exposure (the Roscolux #98).

However I just snagged an SX-70 model 2 (in stylish cream & tan), and successfully modded it too. This camera did have a 1-stop ND filter over its photocell; removing it (see photos at the link above) allows you to get correct exposure with only a Rosco #97 ” Light Gray” gel over the lens.

Conveniently, the first gel in the Rosco sample book is a completely clear one. It’s much easier to cut a new cover for the photocell from this than from a brittle CD case as often suggested. Another bonus of this solution is that the viewfinder image becomes one stop brighter too.

I still found that sandwiching a #05 “Rose Tint” along with the gray gave a more neutral color balance; but I will continue experimenting.

Thus continues my bittersweet Polaroid love affair…

Pinhole camera designs can be incredibly varied. The traditional scout-troop model was built from a Quaker Oats carton, exposing a single sheet of photo paper. But “single shot” pinholes are a bit inconvenient, especially as fewer people have access to a darkroom these days.

So lately I’ve been emphasizing pinhole designs using roll film—like my plasti-pinhole project and it’s siamese twin variant. (I also designed a 120-film camera for shooting 6×12 panoramas, a project you can find in the Best of Make book.)

Pinhole image on Fuji Acros 120 film, taken with a converted 1950s Argus 75 camera

But I’d like to give a little background that applies to all pinhole cameras, of any form. Then we’ll look at a method for fabricating the all-important pinhole itself.

Some Theory

So why does a pinhole camera work? Imagine a light-tight box, with a piece of film on one side and a tiny hole in the other. Each point on the film can only “see” one patch of the outside world, the one lined up with the pinhole—whether it’s light, dark, blue, red, etc. So an image of the scene forms upside down on the film.

With that idea in mind, visualize what happens if you move the pinhole closer: The angle from the film corners to the pinhole gets more oblique, and the camera takes in a wider view of the outside world.

In fact, the distance between the pinhole and the film is exactly equivalent to the focal length of a lens with the same coverage. Hence, it’s most informative to measure pinhole “focal lengths” in millimeters, just as with lenses. (Because a pinhole does not actually focus light, using focal length in this sense is technically a misnomer—but that’s the way most pinhole enthusiasts refer to it.)

So How Large is a “Pin” Hole, Anyway?

Up to a certain point, the smaller the hole you use, the sharper the image you get. But if you go too small, you run into a problem with diffraction—the tendency of light waves to fan outwards when they graze the edge of an obstruction (it’s a problem for lenses, too).

Thus, there is one hole diameter for any given focal length which gives the optimum possible sharpness. Historically, a number of great scientific minds labored to derive the proper formula to compute this. But today, you can just put your faith in a handy online calculator, like this one from Mr. Pinhole.

For typical cameras the best diameter works out somewhere between 0.2 to 0.5 millimeters—equivalent to an f/stop of f/100 to f/300. This definitely implies some long exposure times might be needed. But everything from infinity to inches away will be recorded with equal sharpness.

If you want a camera covering a particular angle of view, you have a choice between using a small piece of film with a short focal length, or building your camera using a bigger image format and a longer focal length. For example, a 30mm focal length on a standard 35mm film frame gives the same coverage as a 225mm focal length exposing an 8×10″ sheet (both show about 72° diagonally). But which is better?

As it turns out, the optimum pinhole diameter scales up more slowly than the focal length: The bigger you build the camera, the smaller the resulting f/stop, and the sharper the image. But eventually, ever-larger image formats can become cumbersome, costly, and impractical. (And besides, if it’s more sharpness you want—you could always use a lens!)

My own conclusion is that 120-film pinhole cameras offer a good trade-off between image quality and film-handling convenience.

How Do I Make a Pinhole?

The goal in fabricating a pinhole is to get one that is nicely circular, without ragged edges, and whose diameter you have at least roughly measured.

You’ll probably do best by piercing your hole in the thinnest possible material. If your pinhole more resembles a microscopic “tunnel,” oblique light rays will be blocked and you’ll get noticeable vignetting. While that effect can be interesting to explore, you’ll likely also see problems from light reflecting off the inner walls of the hole, degrading contrast.

While it’s fine to experiment with tinfoil or the side of a beer can, I settled on a method for fabricating pinholes in aluminum roof flashing (about 0.01″ to 0.02″ thick). I just find it more secure to fasten those flat, stiff sheets into whatever camera I’m building.

First, start by cutting squares of metal 50mm on a side. Why 50mm? Because it’s the same size as a 35mm slide mount—this may come in handy when it’s time to measure the pinhole diameter. Cut several extras, since there’s often a bit of trial and error in achieving your target pinhole diameter.

Place the metal square onto a piece of softwood, and tap a small dimple into the center. A ball-peen hammer works fine; however it might be easier to center the dimple if you hold something like the rounded head of a carriage bolt against the metal, then strike that with the hammer.

The dimple only needs to be high enough that you can selectively rub that spot against a sheet of sandpaper to thin it.

Press and sand the bump against fine sandpaper—320 or 400 grit works well. Here I show the sandpaper wrapped around a block of wood, to make it easier to hang onto; flexing the edges of the metal backwards will help avoid sandpapering your fingertips!

You want to rub with enough pressure that you’re definitely removing metal, but not so aggressively that you sand right through. After a noticeable flat spot has formed, it’s time to start checking your progress.

Gently press the tip of a sewing needle against the hollow of the bump. You are not trying to push it through yet—hold the needle by the sides to avoid applying too much pressure.

What you are testing is whether the metal is thin enough so that the tip of the needle telegraphs a tiny raised point through to the other side. If not, go back to the sandpaper and rub a bit more, then test again.

With your first test, you probably left a small pin-prick in the metal. Keep placing the needle in the same spot after that, to avoid inadvertently forming multiple pinholes.

Once the metal is thin enough for the needle tip to deform it, you should see something like this:

Take a couple of light strokes against the sandpaper to flatten the raised point. Now hold the metal up to a strong light—it’s possible that a tiny hole will show through already. But in any case, you’re getting very close.

Press the bump against a firm backing, like a telephone book. Replace the needle tip into the pin-prick you started, then give firmer pressure, pushing on the end of the needle as shown. You are not trying to push the needle through the metal—the diameter of its shaft is much too large. With gentle pressure you’re just trying to to push the point of the needle through.

Once you “see daylight,” go back to the sandpaper and lightly sand away any rough edges around the hole. Take the tip of the needle and very gently spin it in the hole to help round off any irregularities. Blow through the hole to remove any dust from the sandpaper.

Now It’s time to check if your hole looks clean, round, and what its diameter is.

It’s not necessary to achieve insane precision with your pinhole size. If you have nothing handy but a 10x magnifying loupe and a millimeter ruler, you can sort of “eyeball” whether your hole looks like one third of a millimeter, or whatever. Remember that a hole as far off as 70% or 140% of the desired diameter only means one f/stop of under- or overexposure, respectively. (This is within the exposure latitude for many kinds of film.)

But there are two easy methods to get a more precise measurement: Either use a slide projector, or a scanner connected to your computer. Today far more people have access to scanners than still own slide projectors—so I’ll describe that method first:

Simply put the pinhole metal into the scanner, and scan at the highest available resolution. (Only scan a small selection around the hole itself, to avoid ridiculously bloated document sizes.) Either scanning the hole on a flatbed document scanner or with the slide holder of a film scanner is fine—although a film scanner may offer higher resolution.

Some photo-editing software has a ruler tool allowing you to measure sizes directly. But even in a more basic program (like the old version of Elements shown here), you can still measure the hole. Drag out a selection which just barely encloses its image; then open the “info” palette to read off the size.

A highly-magnified scan of the pinhole; the selection is 107 pixels square. There also appears to be some gunk clinging to the hole that should be cleaned out

To get the most accurate measurement, I suggest going into the preferences and changing the default units to pixels. If you scanned the hole at 9600 dpi, and your selection is 107 pixels across, its diameter equals 107 divided by 9600, or 0.0111 inches. There are 25.4 millimeters in an inch, so that pinhole size translates to 0.28mm.

Personally, I find there is a lot of trial and error in achieving at a nice clean pinhole of the correct diameter. So I will often make a batch of pinholes at the same time, to get one good one. In that case, the scanner method becomes a little time-consuming.

So to me it’s worth setting up an old slide projector with a manual feeder, where I can quickly slap pinholes in and out, and immediately see how they look. This allows me to start with a hole slightly undersize, then nudge its diameter larger (by gently spinning the needle tip in the hole), quickly rechecking until I hit the target size. (Sandwiching the pinhole into a spare cardboard slide mount makes it fit in the projector gate more snugly.)

The key thing is to know that the opening of a standard slide mount is about 23×34mm. From the height of a slide image projected onto the wall, you can calculate the magnification; and from that, you can figure out how large the spot of light would appear from a properly-sized pinhole.

But I have an even simpler trick: Move the projector back and forth until a complete slide is projected at a size of 46 by 68 inches. At that magnification, every inch of the projected image represents 0.5mm at the slide mount. Thus you can read off pinhole sizes very rapidly (a ruler divided into tenths of an inch is helpful).

Measuring the projected image of a pinhole

If you discover you went wildly over your target pinhole diameter, start over with a fresh piece of metal, but try to press more gently with the needle this time. And don’t throw away the “bad” pinhole. Just write its diameter onto the metal using a permanent marker, and hang onto it somewhere. Building pinhole cameras is rather addictive; a day may come when you create another one needing exactly that diameter hole.

Figuring pinhole exposure times means knowing the equivalent f/number. This is simply the focal length of your pinhole camera, divided by the pinhole diameter. (But both need to be expressed in the same units, whether millimeters or inches.) It’s preferable to avoid f/numbers under f/100, just because the correct exposure in full sun will be a fraction of a second—not something most homemade pinhole shutters can time accurately.

When you need to calculate exposure times, few light meters will indicate f/stops all the way into the hundreds! So it’s helpful to know that f/128, f/181, and f/256 are exactly 6, 7, and 8 stops smaller than f/16. Find the indicated exposure time at f/16 and count off the steps to the correct (longer) time needed for your pinhole exposure.

Have fun!

I must confess that in the past, I rarely used Polaroid cameras, finding the “$1 per image” aspect a little daunting. But also, most of their plasticky, auto-exposure consumer models seemed rather lacking aesthetically. (I do make an exception for the SX-70 camera—which still seems as futuristic today as it did when it came out in 1972.)

But in the spirit of savoring our Polaroids while we still can, recently I bought some type 669 film packs.

These peel-apart films are an older technology than Polaroid’s “integral” types like 600 or SX-70 Time-Zero. But the peel-apart pack type was adopted for so many professional and technical uses that demand remained high until digital arrived. So there are several packfilm emulsion types still available. Even Fuji has now started making a line of compatible film packs.

I’m skeptical that another manufacturer will start up making Polaroid’s integral films: It’s a much more complex technology (each pack includes a unique flat PolaPulse battery). But it’s nice to feel I’ll have the Fuji backup option, if I end up falling deeply in love with my pack-film projects.

Anyway, as I mentioned, I was never that fond of Polaroid’s own cameras. This started me thinking about “alternative” ways I could expose images onto 669 film. So today I’ll show the first of two Polaroid camera hacks: The PackPola Pinhole.

This one is so ridiculously easy that it barely deserves the name “DIY project.” Here is the executive summary:

STEP 1: Find a Polaroid microscope camera
STEP 2: Tape an 0.4mm pinhole behind its dark slide
STEP 3: Take pinhole photos

But, oh all right—if you insist on making things more complicated, here are some additional details.

While most of the later pack film cameras were plastic-bodied, Polaroid did manufacture a stout cast-metal body which was used for certain products—in complete cameras, or as a dedicated Polaroid back for technical uses. The model shown (which I was told was a microscope camera) has a rigid cast-metal “pyramid” where a civilian Polaroid model would have bellows, with a custom attachment flange on the front.

Aside from the nice brushed-metal finish, this camera has two useful features. First, it has a real live tripod socket on the bottom (vital for long pinhole exposures). More importantly, its microscope fitting comes equipped with a dark-slide—we can reuse this without modification as the shutter for our pinhole camera. (I gather microscope photos must require long exposures too.)

Now you could build a Pola-pinhole by hacking a regular bellows style camera too—and these models are practically being given away today. You’d need to remove the front of the lens/shutter assembly, and attach a pinhole behind the bare lensboard. (See the excellent step-by-step disassembly photos here—also getting a chance to practice your Italian!) But in that case, you would need to improvise a shutter, and the focal length will be about 30mm longer (and hence less wide-angle-y) than with the microscope camera.

The pinhole is pierced in a thin sheet of metal—the sidewall of a beer or pop can is ideal—and taped inside the “pyramid” behind the shutter. This gives a focal length of about 74mm. (The diagonal of a packfilm image is about 120mm, so this yields a wide-angle coverage similar to a 28mm lens on 135 format.)

For that focal length, the optimum pinhole diameter is roughly 0.4mm or 0.015 inch. This equates to a pretty tiny f/stop: the nearest whole stop value is f/181. That’s 7 stops smaller than f/16—useful to know when trying to translate light-meter readings into pinhole exposure times.

Back up your pop-can metal against something firm like a phone book, then just barely pierce the metal with the tip of a sewing needle—don’t poke all the way through! Sand away any rough burr around the edge of the hole using fine 320 or 400 grit emery paper. Twirl the needle tip in the hole to smooth any raggedness—you want the hole to be nice and round.

You can measure the diameter of your pinhole exactly, by placing it on a flatbed scanner and scanning at the highest possible resolution. Knowing the exact DPI of the scan, and reading off the dimensions of a selection just including the hole, you can see if its diameter is in the right ballpark.

I often start with a bunch of metal blanks of 50mm square, a size that will fit inside a cardboard 35mm slide mount. By setting up a slide projector at a known magnification, I can quickly go back and forth between checking sizes and roundness and gently enlarging holes with the needle to reach the desired diameter.

Of course, one great advantage of a Polaroid pinhole is that you can just wing it. Try an exposure at what you think your equivalent f/stop is. If it’s too light or too dark—next time use a revised guesstimate of your f/number when you figure the exposure.

Polaroid 669 is well-known for “interesting” color shifts when developed in cold temperatures; but also when using the kinds of longer exposure times needed for pinhole work. With a multi-second-long exposure under open sky light, you can have quite a strong blue/cyan cast:

You might enjoy this effect—or, you can tape a warming filter in front of the pinhole.

In direct sun, start by trying one of the #81 series filters. But for longer exposures or in cooler light you may need a stronger orange/salmon colored filter, like one of the #85 series. If you can get your hands on a swatch-book for theatrical gels (like Roscolux), that would offer a huge range of colors to try (with pinhole work, you’re not exactly worried about the optical flatness of the sheets).

Personally, I raided my cache of oddball Series VI filters, and found a perfect Harrison brand color-correction filter, designated “C3.” This filter loses a little less than one stop of light; I used exposures of about 3 seconds in full sun, up to 30 seconds in darker shade. The color palette of 669 seems to give a nice pastel softness, thought without much saturation in the reds & yellows.

If you have never used pack film before, you may be flummoxed by the profusion of weird tabs that sprout from the end of the camera (from a slot helpfully labeled “4″). This becomes easier to explain when you understand that pack film is actually negative and positive sheets stored separately, which need to be sandwiched together to start development.

The first black tab pulls a light shield out of the way, and uncovers the top negative sheet. After you make an exposure, pulling a white tab slides the exposed negative around into contact with the positive print paper. However both are still dry at this point, and nothing happens yet.

Pulling out the wide arrowed tab bursts a pod of chemical paste, and the two chrome rollers smoosh a uniform layer of this goo between the positive and negative, starting development. After 60 seconds, the image is fully transferred and you can peel the print away. It stays a little tacky for a few moments, so don’t accidentally get it stuck to another print.

I discovered pretty quickly that my microscope camera pack-holder had a couple of quirks—possibly the reason why it had been retired and discarded in the first place. The first is that its rollers seemed to have gotten tired, and weren’t spreading the developer goo all the way to the far edge of the print. But actually, the white blobs caused by this were one of those serendipitous creative accidents that I ended up liking.

The other issue was that there was a serious light leak somewhere in the camera body. Now, remember that a pinhole (like a lens) forms its image upside-down. So this radiant splash of light at the bottom of the print was coming from somewhere on the top of the camera.

Eventually I realized there was a tiny gap at the seam where the pyramid cone attached to the film back—perhaps the camera had gotten dropped once. A bit of electrical tape fixed that up. But as light leaks go, this may be one of the more beautiful ones I’ve seen!

One rationale for that project was that nowadays, it’s getting harder to buy and develop any film size besides 35mm. Pinhole cameras made for other odd formats are certainly fun, but sometimes require access to a darkroom to make them practical.

But one of the joys of pinhole photography is being able to try out bizarre, idiosyncratic camera designs: Weird-shaped frames, ultra-wide-angle coverage, or warped perspectives from curving the film plane.

The moderately wide coverage of the normal plasticam pinhole is interesting; and its standard 24×36mm frame makes developing the film at any lab easy. Yet compared to more exotic possibilities, it does begin to seem a little tame…

A Japanese woman on Flickr wanted to make a panorama-format pinhole camera. Her inspired idea was to take a plastic Holga, and saw it into pieces. She reused its film-supply and take-up-spool compartments, but replaced the middle section with a homemade “stretch limo” version: A light-tight box with film gate, pinhole and shutter. Genius!

A Holga uses 120 film of course; but she inspired me to consider doing something similar with 35mm film. (Aside from getting interesting widescreen framing, with pinhole cameras a larger format helps give a more detailed image.)

The way I build a 35mm plasti-pinhole, the original shutter is discarded; so it’s not the button on top that takes the picture any more. But the film-winding mechanism remains intact. As you wind, a toothed wheel allows 8 sprocket holes to go past, then locks; this yields the standard-width frame spacing. You still need to click the button on top to release the winding thumbwheel, before you can advance to the next frame.

But you do this independently from making the exposure. And I had an “aha” moment when I realized that if you clicked and wound twice between pictures, that standard mechanism would permit shooting double-width images: 24 x 72 mm!

But how to build the rest of the camera?

Here is my whimsically warped solution: I took two identical plastic trashcams, and sawed through them, exactly at the edges of their film gates. Then I glued and taped them back together “siamese-twin” style, to make a panoramic pinhole camera.

Two focus-free plastic 35mm cameras; $1.40 for the pair at my local thrift store.

A majority of trashy plastic models use curved film gates, to mask the deficiencies of their crummy lenses. But for this purpose, finding two matching cameras with flat film gates makes construction much simpler.

Some plasticams have their own “panorama” mask which you can swing into place. But all those extra parts would add more complications, so I shunned that style too. These two ultra-simple Bell & Howell trashcams turned out to be perfect.

I arbitrarily chose one camera for the supply-compartment half, and the other for the film takeup side. Then I disassembled both cameras and discarded all the unnecessary bits and pieces inside—lenses, shutters, springs, etc. It’s important to remove all stray metal parts before sawing into the camera body!

Discarding useless innards; black lines mark the approximate cut locations

Unlike in my standard plasticam-pinhole, I could not reuse the sliding lens guards as a shutter: The pinhole opening would not be aligned with either camera’s original lens position. So all those moving parts got tossed too.

Next I screwed the shells back onto the camera bodies, wrapped tape around both to hold their backs shut, and sawed through each one.

The crapcam types shown here include dummy weights glued into their bases (to lend an illusion of quality!) It was particularly tricky to avoid grinding the saw blade into those metal chunks—so be careful. An old hand-saw miter box is a great tool for getting a straight, square cut.

I sawed just inside the right edge of one camera’s film gate, and the left edge of the other. This still left some interior partitions standing in the way of the desired pinhole location, all of which needed to be cut away with a sharp knife.

Now, I wish I could say I used some sophisticated assembly technique to combine the two bodies. But really I just spooged the halves together with copious amounts of black silicone sealant—supplemented with much electrical tape. I was trying to fill all gaps where light might leak in, and keep the now-combined film gates as well-aligned as possible.

I also glued an aluminum bar across the two film-door halves, so the back would swing open and latch shut correctly as a single unit again.

A piece of aluminum sheet with an 0.2 mm pinhole went across the front of the camera body. Positioned only 26mm from the film plane, I knew this camera was going to give some wide-angle coverage! (Horizontally, it’s about 110°.) The pinhole size works out to f/128, for those of you keeping track.

For this camera I tried a new shutter idea, a design which has quickly became my absolute favorite. I will definitely be using it again for any future pinhole cameras.

I took a spare cable release I had lying around, and cut away the rotating barrel intended to thread into a shutter button. This uncovers enough extra length of the moving shaft to allow me to hot-glue it to a piece of thick black cardboard. Then the cable sheath is glued to the front of the camera body.

The moving shutter piece is outlined in red here. It has a cut-out which uncovers the pinhole as the cable release is pressed. A couple of scrap pieces glued around the edges guide the moving panel.

What’s wonderful about this design is that the cable-release’s own internal spring snaps the shutter closed again—or, it can be locked open indefinitely with the set-screw of the release. And there’s no jiggling the camera when you open the shutter.

The front shell of the camera needed a matching rectangular opening cut into it. Then finally, I screwed and taped the camera shell back together again. (There’s no particular significance to the metallic tape—it just hides several no-longer-needed openings in the camera’s front panel.)

The block of particle-board contains my usual homebrew tripod socket: A 1/4-20 nut epoxied into a hole in the bottom.

For a while I was jokingly calling this camera the “HaxPan,” in reference to Hasselblad’s multi-thousand-dollar panoramic XPan camera system. Of course, my camera covers a wider angle than even its 30mm lens (as well as saving a few pennies… )

Obviously no ordinary lab will know how to make prints from these crazy non-standard frames. But the negatives can be developed just like any other 35mm, and then scanned on any of the current inexpensive flatbed film scanners for further processing.

Making this camera was truly an experiment. There are still a couple of small light leaks at the joint between the cameras. And next time I would probably do a few things a little differently…

Placing the pinhole so close to the film does give extremely wide views—but you can’t see much detail at the edges, because the light fall-off is so extreme. And a 110° angle of coverage is so hard to visualize without a proper viewfinder that I found framing to be quite hit-or-miss.

So next time, rather than placing the pinhole so far back, I would build up the light-tight inner compartment a little deeper and use a slightly longer focal length.

But that’s the great thing about pinhole cameras: The cost of experimenting is low… and the fun of blazing new ground is priceless.

Happy hacking!

Sample photo from the double-width 35mm pinhole. Note small light leaks at the seam between camera bodies. More samples here.

But recent photography magazines and books offer little help at giving these “switchers” an introduction to film basics—one of the reasons I began this blog. So today’s column is a welcome to all those total film beginners out there. Hi!

You’ve probably discovered that getting film developed today can become a headache —whether due to a shortage of local labs, unreliable service, or high prices. That’s particularly true for folks using 120 film (for example, in a Holga or Diana+). So you may have heard the advice, “just develop it yourself!”

But what’s involved in doing that—and is it expensive? This post will talk about the supplies you need for developing film at home. To do your own negatives, all you need is this:

Developing tank, measuring graduate, funnel, thermometer, stirrer. Developer, stopbath, fixer, and Photo-Flo

The good news:

You do not need a darkroom to develop negatives. You only need darkness briefly, to load the film onto the reel of the developing tank. The tank is lightproof, so after loading it you can do the all the other steps in a day-lit kitchen or bathroom. (Darkrooms are for making prints.)

The cost of the chemicals is much cheaper than commercial developing. You don’t need to drive anywhere, and you can control the process to your own tastes. The developing steps are not any harder than following a cooking recipe.

There is a very plentiful supply of used developing gear today, since so many photographers have gone entirely digital. If you start asking around, you might find that an acquaintance or family member has old equipment they’d be happy to give away (don’t trust any old already-mixed solutions, though). Even buying everything new should not cost you more than $50.

And the bad news?

We are talking about developing traditional black & white film here, not color. It is possible for amateurs to develop color at home, but the chemistry is not so beginner-friendly. But black & white has a certain timeless beauty, so you may discover new creative directions if you’ve never tried that before.

Okay, once you have the negatives—what do you do with them? Well today it’s quite common to scan them, then work with the computer file just as you would with any digital-camera shot. For US readers, a great source of inexpensive film scanners is the refurbished “PHOTO” models from Epson’s online store. Schools & universities may have scanners available for their students—or traditional darkrooms too, if you choose to learn that craft.

Photo chemicals are no more toxic than household cleaners; but you’ll want to take care to avoid inhaling any dust if you mix your solutions from powders. And the chemicals can sometimes smell funny.

I’m going to talk about which supplies you’ll need—not give full step-by-step instructions how to develop film. But there are many other descriptions of the steps on the web. (For example here; or with more photos here, or in this 200kB PDF from Ilford.)

As seen above, you’re going to need a few quart/liter bottles, some kind of graduated measuring vessel, and it’s helpful to have a funnel. These don’t need to be “official” photography supplies. But if you improvise using things found around the kitchen, be sure to label them clearly as for photo-chemical use only.

The first piece of dedicated equipment you’ll need is a developing tank. There are several types, each with its own minor advantages and disadvantages. But all will work fine.

The tank shown here is an older style Paterson System 4. These were extremely popular with 1970s/1980s amateurs, inspiring several lookalike imitators. You will still find many of these floating around.

The current Paterson style is similar, but with a redesigned wide-mouth top (if you google for more information, note that the company name has only one “t.”) The reel flanges twist apart to adjust to different film widths—the 35mm spacing is shown above.

Beginners often find the most daunting part of developing film is getting the strip loaded onto the reel (remember this must be done blind, or light would fog the film).

Paterson reels have little ball-bearing widgets which help push the film onto the flanges, using a back-and-forth twisting motion. My experience is that beginners find this style easiest to learn; the minuses of the Paterson-style tank are minor in comparison. (One tip is that the reels must be absolutely dry before loading.)

First-timers often ask for advice in online forums about which developer to buy—then get overwhelmed by all the passionately conflicting suggestions. I think the most important thing say is, don’t worry about it! The difference in image properties between developers is not large; and if you end up scanning your negatives anyway, that stage has a much greater effect on the tonality of the image.

Having said that, Kodak’s D-76 is considered a classic, an excellent all-round developer. It’s a perfectly fine place to start. (Other developers are more “specialists”—e.g. increasing apparent sharpness, but at the cost of greater graininess, etc.)

You mix up 1 liter of D-76 stock solution according to the package directions, but must let it cool before using. I suggest not re-using that same stock solution over and over (allowing it to become exhausted). Instead, use it diluted 1:1 with water—mixing just enough to cover your reel(s) before use, and then discarding after. Note that development times for the 1:1 dilution are longer, and will be listed separately from the “straight” D-76 times.

My personal favorite developer is Kodak’s HC-110, a thick syrup concentrate. HC-110 yields image properties similar to D-76. With HC-110, I also mix up just enough solution for each film right before use. But the syrup is so concentrated that I must use a 12ml syringe to measure it (no needle, though!).

After opening the bottle, the syrup will stay fresh for more than a year. The only downside for the occasional user is that one bottle can develop 50+ rolls; and if it takes you several years to get through that, you might have a problem.

Spec sheets usually specify development times at a temperature of 68°F/20°C . The rate of development increases with temperature, so you will need an accurate thermometer to measure this. The traditional darkroom thermometer has a big glow-in-the-dark dial; but if you have trouble locating one, it’s fine to pick up a cheap digital kitchen thermometer instead.

After the emulsion of your film has been wetted, it’s rather tender; so it’s important not to shock it with any sudden changes in temperature. You also use your thermometer to insure that the successive steps remain within a few degrees of the developer’s temperature. I usually fill the pink plastic tub seen above with tap water at 68°F/20°C, then set the stop and fix bottles in it for an hour or so before starting. Afterwards, that water can be re-used for the first few rinse baths.

“Stop bath” is a weak acid solution. It does not have any effect on the image itself—it’s simply a rinse, which halts the developing action very quickly and uniformly. The traditional stop bath had a distinct vinegar smell (which is essentially what it’s made from); many folks substitute a plain water rinse instead, with (apparently) no ill effects. Stop bath is so cheap that I’ve always used it, however.

It does not matter in the slightest which brand of fixer you use: You can choose entirely based on whichever is available and convenient for you.

I prefer the liquid-concentrate fixers; but my local stores have stopped stocking them, so it’s back to powder for now.

What you do need to understand is that different types of fixers work at different rates; and furthermore different emulsion types fix at different speeds. The general rule is to open the tank lid at 1 minute and observe how long it takes until all the cloudy, milky haze disappears from the film; then continue fixing until twice this time has elapsed.

The final step of developing is rinsing the film and hanging it up to dry. If your tap water temperature is too cold, it won’t be effective at rinsing away the fixer residue (which then could form brown stains). It can take a bit of fiddling with the taps to get them flowing at a constant 68°F/20°C temperature. But don’t blast the film with hot water or the emulsion will go all wrinkly!

If your tap water contains a lot of minerals, drying water droplets can leave white, crusty rings on your negatives. So one optional final step is to end with a rinse of distilled water; or use a wetting agent (such as Kodak’s “Photo Flo”) to help water sheet off the negatives. Shedding water more quickly helps the negatives dry faster, too.

I did not show the weighted metal clips which many people use to hang up their wet film; they aim to minimize curling as the emulsion dries. But that’s something you can easily improvise with clothespins, binder clips, etc.

What is most important is that you find a sheltered location to hang your film, where air currents won’t be wafting dust and lint onto your damp, sticky emulsion. And even though you will certainly be dying to peek at how your first negatives came out, be patient! The tender emulsion needs to dry completely before you start handling it.

Good luck!

What made mercury button cells so appealing was that their voltage stayed absolutely ruler-flat, until the last of the chemicals were depleted. After that, the battery quickly died. Most camera makers omitted any voltage compensation in their meter circuits, and simply used the battery itself as a voltage reference.

Mercury PX-13 battery, curse of vintage camera-dom

By far the most common size used in older cameras was the PX-13 or PX-625 type. Its case had a raised shoulder around its minus end, making it look vaguely muffin-like.

Today we recognize mercury to be a highly toxic metal; and worldwide, mercury battery production has been phased out. Any stocks of mercury batteries now remaining are from old production runs—a safe guess being from sometime in the last millennium.

If you go shopping for a PX625 today, you’ll discover lookalike replacements being sold. But they are alkaline cells, not mercury. And the problem is, a mercury cell is a 1.35 volt battery. An alkaline cell starts out at about 1.55 volts instead.

In a calculator, kitchen timer, etc., this voltage discrepancy is unimportant. But a light meter works by measuring the exact current flowing through a photocell: so the wrong voltage can wreak havoc with accurate readings. A few cameras (notably Pentax) used a meter circuit which was insensitive to voltage variations—but for most meters, wrong voltage means wrong exposure.

Worse, an alkaline battery actually drops off in voltage as it’s used, so the error is not even consistent—really you get the worst of both worlds. (The same drooping-voltage problem applies with 3-volt lithium batteries, in applications where those could be used.)

But silver-oxide batteries are widely available, and maintain a flat voltage (of about 1.58 volts) over their whole lifetime. The long life of silver-oxide cells make them the first choice anywhere it’s possible to use them.

Meter-Battery Voltage: Myths & Reality

Sometimes you read confused internet discussions about whether this o.2-volt error is important. And some rather questionable assertions get repeated. One claim is: “modern film has such wide exposure latitude that it doesn’t matter.” Another is, “you can just change the ASA setting to compensate.”

Fortunately, I am lucky to own one last genuine, mercury PX-13 cell, which still has some juice to it. So I decided to make a definitive test for myself.

I took light meter readings using two classic old-school SLRs (an Olympus OM-1 and a Canon FTb), and compared them to a known-accurate Pentax V spotmeter. Using the intended mercury battery, I got the camera and the spotmeter to agree within about 1/2 stop, over the entire range from full sun to dim indoor light.

But with the higher voltage of a silver-oxide battery, the cameras’ meters gave incorrect readings—and with a strange pattern: In bright sunlight, the indicated readings would yield two and a half stops underexposure! Yet in dim indoor light (at about the limit for handheld shooting) the meter readings were nearly correct. Between those two extremes, there was a variable amount of underexposure.

Well, this demolishes both of the internet myths I mentioned. First, 2-1/2 stops of underexposure is a terrible idea with any negative film I know of. (You’d get ugly grain and totally blank shadows.) Second, there is no simplistic way to adjust the ASA to compensate, because the error is not consistent as you go from bright to dim light.

The errors could certainly be different for other brands of cameras, using different circuit designs. There is no substitute for checking your own equipment against a known-good meter. But obviously the problem is a real one.

Frans De Gruijter has written the definitive article on this problem, along with several solutions, downloadable here (500 kB PDF). This article goes into dense technical detail; but at the very least, look at the graph he provides on page 3, showing the voltage curves for several different battery chemistries.

And there you’ll notice an intriguing possibility: Zinc-air batteries.

Zinc Air?

Zinc-air is an interesting battery chemistry, giving excellent energy density at low cost—advantages that have made them the preferred power supply for hearing aids. Happily, zinc-air cells have a voltage quite close to that of mercury cells. And this voltage stays consistent over the battery’s lifetime, just as we’d like.

Pull the blue tab to activate the battery

Zinc-air chemistry is also the basis of the “Wein cell,” often sold in camera stores as the correct-voltage replacement for mercury photo batteries. However the cost of vanilla #675 hearing-aid batteries is much lower—about $6 for a pack of 8.

To use either of these types, you must pull off a sticky tab first, which allows air to enter pinholes in the battery case. The battery does not produce any voltage until oxygen reaches the interior. Unopened cells can be stored for many years and remain fresh.

But one downside is that the inside of a zinc cell must remain moist for the chemical reaction to work. In arid environments, the cell can dry out and stop working after just a month or two, before its electrical capacity has been used up.

Putting the sticker back over the air holes will prolong the battery’s life, if you can remember to do it. But with the low cost of hearing-aid cells you might just consider them expendable, replacing them often.

The 675 size hearing-aid battery is a little bit thinner than a PX13 mercury cell; also it lacks the “muffin” shoulder and so is smaller in diameter. Sometimes you will need to add a little spacer ring to keep it centered in the battery compartment.

For this, I just slice rings off the end of a piece of tubing of the proper diameter:

Others have suggested getting a rubber O-ring from the hardware store; and Rick Oleson shows a neat solution using a loop of copper wire.

Now, the voltage of the zinc-air battery is not perfect—it can be a shade too high. In fact, both the Wein cell and hearing-aid solutions have some voltage quirks, which I plan to write about in another article. However let’s keep things in perspective:

Over 40 years, any light meter might drift out of calibration—even if supplied with the textbook 1.35 volts. The shutter speeds on a vintage camera could easily be out of adjustment by a half a stop or so. There can be some slop in aperture linkages, so that you aren’t getting precisely the marked f/number. Vintage cameras are not the place to look for 3-digit precision.

But my tests say that a zinc-air hearing aid battery will get you to within half a stop of the exposure reading you’d get using a mercury battery. And any error will be worst in bright sun—the one situation where it’s most reliable to trust those old “Sunny 16″ instincts.

So if all that’s stopping you from taking some nice old camera for a spin is the mercury battery issue, go with the zinc-air cells. It’ll get you out there shooting after one quick, inexpensive trip to the drugstore.

Then you can explore other, techier solutions to the problem later, if you choose to go that route.

Update: More on the quirks of zinc-air battery voltage in this follow-up post.