Most rely on a well-proven Gaussian formula, whose nearly-symmetrical configuration automatically reduces certain aberrations like barrel distortion. The fast maximum aperture provides several benefits: A bright viewfinder image that “snaps” into focus, and the potential for pleasingly shallow depth of field.

Some photographers prefer a slightly wider lens as their “normal,” but on the 135 film format the typical 50mm focal length yields a very natural, neutral perspective.

Fast “normal” lenses—why are they such rarities in digital photography?

When one looks at the lens options for digital SLRs, however, the choices become a little murkier. By default, most DSLRs come equipped with kit zooms, with unavoidable penalties in lens size and maximum aperture. Many of these reveal quite obvious barrel distortion when zoomed to their widest setting.

On the other hand, fast 50mm primes are still offered by most cameramakers—as holdovers from their earlier film-camera lens lineups. Yet on a typical DSLR with a cropped-format sensor, these stop being “normal.” Instead they function as short portrait lenses.

That’s useful in many cases, to be sure; but it’s not the classic “all rounder” lens that 50mm represents on a traditional film camera. True, Sigma does offer a 30mm f/1.4 designed as a normal for cropped-format DSLRs; but its near-$500 pricetag is quite a shocker compared to past film-camera equivalents.

Recently, my eye was caught by an Olympus DSLR, the E-420. With this model Olympus has finally delivered on their original promise of very compact camera bodies through the use of a new “Four-Thirds” sensor format, one about half the width of 35mm film. In fact the E-420 is one of the few DSLRs whose size compares to the classic Olympus OM series of film bodies.

And even better, Olympus was pairing it with a new (non-zoom) lens—an impressively-tiny 25mm f/2.8 pancake. This focal length yields “normal” coverage on the smaller sensor format.

But an f/2.8 maximum aperture is hardly going to set pulses racing among serious available-light enthusiasts. And unfortunately, a recent lens test at DPReview.com shows that the new pancake is only a middling performer. Even this digital-specific, blank-slate design showed significant barrel distortion, as well as (freakishly) chromatic aberration even near the center of the frame.

Olympus is known for making some of the best-respected DSLR lenses today; yet their struggle was to design a well-corrected lens when the flange-to-sensor distance is significantly longer than the focal length. The classic symmetrical configurations don’t work in that case; so various optical shenanigans are required which inevitably degrade performance.

At this year’s Photokina photo trade show, Panasonic caused a great deal of buzz with an announcement of their Lumix G1. Panasonic seems to have recognized that the Four-Thirds format has never gained much traction with enthusiast DSLR buyers; yet it would offer consumers vast improvements in image quality over today’s teeny-chipped point’n’shoots, if only the camera body could be shrunk to acceptable size.

Panasonic’s way to achieve this was to omit the reflex mirror entirely (meaning only electronic viewfinders are possible), then halve the flange-to-sensor distance. This is the essence of a new “Micro Four-Thirds” standard, of which the the G1 is the first example coming to market (shortly).

Olympus showed their own prototype of a Micro Four-Thirds camera, made even more compact by omitting any eye-level viewfinder. This emphasis on small body styles has led some to hail Micro Four-Thirds as the arrival of the “digital rangefinder”—i.e. very compact cameras with interchangeable lenses.

Photo: 1854, the blog of the British Journal of Photography

Even the ribbed lens of the Olympus prototype seems reminiscent of certain 1970s compact RFs, like the much-loved Canonet QL17 GIII. (Note that the BJP article calls the prototype an “SLR,” which it is not: “R” stands for “reflex” viewing, precisely what Micro Four-Thirds models lack.)

But to me the most intriguing footnote to these announcements is buried in Panasonic’s future “Lens Roadmap.” In 2009, allegedly they will introduce a non-zoom, 20mm f/1.7 lens in Micro Four-Thirds mount. If we translate that to its equivalent on 135 film, this would be a fast 40mm lens—actually, just like 1972’s Canonet!—with a “wide normal” coverage that I would personally love. And because of the reduced flange-to-sensor distance, its optical design might even be a simpler, well-corrected symmetrical design.

So will compact, fast, well-corrected normal lenses come to digital, at long last? At a price we can afford? This remains to be seen, though I’m cautiously hopeful. But for the moment, virtually any random 35mm SLR from the past, equipped with its humblest possible lens option, offers something that remains a rarity in the world of digital.

I had been taking photographs for over 30 years before ever hearing the term; and at first it confused me too. However it turns out that bokeh refers to quite a specific aspect of lens blur—calling attention to subtle phenomena that might otherwise be overlooked.

Unfortunately though, the meaning of “bokeh” has been getting rather blurred itself lately. We ought to make a stand to preserve its specific technical meaning, before this useful term degenerates into just another name for “fuzzy.”

A corny flower shot shows nice bokeh from a rotten plastic lens (on a vintage Diana)

Now don’t get me wrong—photographs which use selective focus to give nicely blurred backgrounds can be very pleasing. I like this effect, and have written about how to get it. And because many of today’s digital cameras limit your ability to achieve this look, a photo with shallow focus and a creamy blurred background will often attract many admiring comments about “great bokeh!”

But bokeh is NOT a synonym for “blurry background,” or “shallow depth of field.” It actually has little to do with the amount of blur. The degree of blur you see in out-of-focus areas is essentially a function of geometry—the relationship between the aperture’s diameter and its distance from the subject. Lets say you’re taking a portrait from 4 feet away using a 50mm lens at f/4. Every brand and every design of 50mm lens will render the background with the same amount of blur. But to the connoisseur, two different lenses may yield violently different bokeh.

Bokeh refers to the subjective quality of the blur. Is it “jangly” and busy-looking, or creamy and smooth? Do out-of-focus highlights have odd, distracting shapes, or are they unobtrusive circles? Does the blurred area seem to “swirl” around the center of the photo in arcs? These are some of the factors which might be mentioned as aspects of the bokeh for a particular lens. And these may be the reasons why a serious bokeh geek would chose one particular lens over a different brand with otherwise identical specs.

The word “bokeh” officially entered the English language in 1997, in an issue of the magazine Photo Techniques—whose editor Mike Johnston decided to add the final ‘h’ to make the pronunciation less ambiguous. He tells the story here, and includes some interesting photos showing different subjective effects in various blurred backgrounds.

Where does Bokeh come from?

But WHY might different lenses have different bokeh signatures? Well, there are two effects.

Each point of light from an unfocused area of the subject forms an extended bright patch at the image plane. Conventionally we call this a ‘blur disk,’ as if these were always circular; but really the blur spot takes on the same shape as the lens’s aperture stop. If the diaphragm blades form a 6- or 8-sided “stop-sign” shape (as SLR lenses typically do), so will the blur spot.

A most extreme example of this happens with mirror telephoto lenses, which have a central obstruction: Their blur disks are fuzzy doughnuts. This creates exceptionally distracting bokeh, if there are pinpoint highlights to accentuate it.

This crop from an Olympus XA shot shows busy diamond-pattern bokeh, matching the shape of the camera’s simple 2-blade aperture stop

Also, if a lens’s barrel design obstructs the more oblique light rays, the effective aperture opening becomes progressively more football-shaped towards the corners of the frame. This often leads to a “swirly” background effect if the lens is used at wide apertures.

The other issue has to do with a subtlety of optical design; namely, whether the blurred light ends up more concentrated at the middle of the blur disk or at its edges. A bright rim to the blur disk generally leads to distracting, jangly-patterned bokeh. But note that this effect often reverses depending on whether the subject is in front or behind of the focus point.

Both these effects are discussed in much detail in this excellent article (it is actually one of the original 1997 Photo Techniques articles mentioned above).

A blur disk with the light concentrated more towards its center will generally lead to smoother, creamier bokeh—and ironically one way to achieve this is to create a lens design which leaves some uncorrected spherical aberration. That compromises overall sharpness, so lens designers usually avoid it.

But there have been some specialized soft-focus lenses manufactured that exploit the effect; and it’s the reason why a plastic piece-of-junk camera often gives such dreamily smooth blur where the subject is out of focus, like in the Diana daisies shot I posted above.

————

Update: This page from Rick Denny compares the bokeh from several lenses of similar focal lengths; it illustrates very well how differently each renders out-of-focus highlights (scroll down the page to the photographs).

The film ends with some rather cosmic commentary by Philip Morrison, who also collaborated on the classic Eames film Powers of Ten.

Vox sez, “check it out.”

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.

.

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.

The museum shows several camera lenses cut open—one of which appears to be a Leica Tri-Elmar-M:

I realize this museum is in Berlin, and thus wants to showcase Germany’s well-regarded optics industry. Still, it’s a bit heart-stopping to note that this particular Leica lens is now out of production, and was hardly an inexpensive item—one currently for sale on eBay has a “Buy It Now” price of USD $3,350!

This is an unusual lens for M-mount rangefinder cameras, that can be switched to 28, 35, or 50mm focal lengths. Note that it is not exactly a zoom lens, as only those three discrete focal lengths are available. (This makes sense on a rangefinder camera, where the viewfinder also switches between several discrete choices of frame lines.)

It’s actually rather impressive that the lens achieves this (and has a good reputation for sharpness to boot) with so few lens elements (8 elements in 6 groups).

If you were interested in my past post about simple camera-lens design, check out the link. The complexity that goes into sophisticated camera lenses can be pretty impressive.

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…