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Why Can’t Digital Be Normal?

Published October 7th, 2008 in Optics, Mechanics, Electronics, Photo Zeitgeist | 1 Comment »

A simple luxury that 35mm photographers take for granted is the ubiquity of compact, well-corrected normal lenses—ones with maximum apertures ranging from f/1.8 to f/1.4.

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 Lens on 35mm

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.

Olympus Micro Four-Thirds Prototype

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.

Bokeh: What it is and isn’t

Published September 17th, 2008 in Optics, Mechanics, Electronics, Photo Zeitgeist | No Comments »

The word “bokeh” is the Japanese word for blurry; and based on skimming Flickr comments recently, it seems to be the buzzword of the moment in photography circles. There’s a puzzle, though. Since English already has the word “blur,” why did anyone feel a need to start using the Japanese one? It’s also odd for the word to be transliterated with a final ‘h’; after all, we write sake and not sakeh.

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.”

toycam bokeh sample

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.diamond bokeh

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.

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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).

Polaroid Addendum: Eames Film about SX-70

Published September 6th, 2008 in Optics, Mechanics, Electronics, Polaroid | No Comments »

I’m a fan of the design work of Charles & Ray Eames, so I was tickled to find a film on YouTube they did for the introduction of the SX-70. It’s part advertisement, and part user guide; but also gives a cool inside look at how the mechanism works. The Polaroid images shown are nicely inspiring, though there’s a bit of a pang of loss viewing them today (especially seeing all that original SX-70 film with its turquoise “opacifying layer” being shot).

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.”

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