handheld duellists

Up until now, the ultimate low light lens appears to have been the modified Zeiss 50mm f/0.7 Stanley Kubrick used in the candle-lit scenes of Barry Lyndon. Depending on who you ask, these scenes were either completely, or at least primarily lit by the candles you see in the picture.

Kubrick also had a second Zeiss 50mm f/0.7 modified to become a 36.5mm f/0.7. Because there is less apparent motion blur due to camera shake at 36.5mm than at 50mm, this second lens is then the gold standard for handheld, low-light lenses.

While no lens with a maximum aperture of f/2.8 can hope to compete with an f/0.7 lens when it comes to freezing moving subjects, still subjects are another story. Here, you can choose as slow a shutter speed as you want (within the limits of sensor noise), as long as the camera stays still. The traditional, and still most fool-proof way to do this is to use a tripod (or a dolly or crane for motion pictures). But, post 9-11, the number of places you can use a tripod are shrinking.

Enter Image Stabilization

For its latest lens-based image stabilizers, Canon claims the ability to take comparably-sharp pictures at three stops slower shutter speeds than what is possible without IS. For a given sensor format, the ability to hold a camera still enough to avoid significant motion blur is roughly proportional to the focal length. Thus, I can hold a 17mm lens at shutter speeds about one-half that of a 34mm lens with equivalent probability of significant motion blur due to camera shake.

So let's add up the stops. The Zeiss 36.5mm f/0.7 has an aperture four stops faster than the maximum aperture of the Canon EF-S 17-55mm f/2.8 IS. The Canon has a three-stop advantage due to image stabilization, plus just over a one-stop advantage at 17mm versus 36.5mm. -4 + 3 + 1.2 = 0.2. That is, for still subjects, the new Canon just edges out the previous Zeiss champion.

Caveats:

- These calculations are based on rules of thumb and probabilities, not deterministic physics, so they are not nearly accurate enough to say the Canon is the definitive winner. Even if the assumptions are correct, it's effectively a tie.

- To repeat: this only applies to still or slow-moving subjects and still photography. If you want to recreate Barry Lyndon, the Canon f/2.8 IS lens won't hold a candle to the Zeiss f/0.7.

Tie-breakers

If these two lenses are indeed virtually equivalent in their ability to produce sharp images handheld with still subjects, the new Canon has several practical advantages. First, even at a relatively wide 36.5mm, f/0.7 gives you very little depth-of-field: under two inches at a subject distance of five feet. At 17mm, f/2.8 gives you three feet in focus at the same subject distance. This makes a huge difference in the ability to get the subject in focus when using the camera handheld. Second, the Canon is probably much smaller and lighter than the lens Kubrick used. Third, and most important, the new Canon is expensive at $1179, but I'm guessing the Zeiss would be at least several times that price.

Conclusion

So, if freezing action at the lowest light levels is your paramount concern, the Zeiss 36.5mm f/0.7 is your lens. If your subject has little or no movement, or you want selective motion blur, or you don't have an $11 million budget, or you just don't want to deal with a large, extremely-rare, fixed-aperture, manual focus, prime lens, the new Canon EF-S 17-55mm f/2.8 IS is the last contestant standing.

Followup

Apparently, Kubrick used ISO 100 film for Barry Lyndon, and according to this post, his cinematographer John Alcott claimed the light levels in the candlelit scenes were about 3 foot-candles. This works out to just short of EV4. The same set of articles cited mentions that the entire film was pushed one stop. By definition, then, the fixed f/0.7 lens meant their shutter speed was 1/50th sec.

Assuming the field of view of the 36.5mm lens on the reduced cinematographic frame can be matched by the Canon 17-55mm, it should then be possible to duplicate the scenes from Barry Lyndon with the same shutter speed but ISO 3200 instead of (effectively) ISO 200 - handheld, and without the IS system even breaking a sweat.

If we go to the wide end of the lens and let the IS system rip, according to the 1/(effective focal length) rule of thumb for handheld shutter speeds, the Canon should be able to remain steady at 1/3 sec. (3 stops below 1/25 sec.). That's four stops faster than what was needed for Barry Lyndon, or just below EV0. The autofocus system on the Digital Rebel won't even work in that little light.