The Risks and Rewards of Fast Lenses: Part II

This was shot handheld with a Sigma 30mm f/1.4 HSM at 1/90 second at f/2.0 and ISO 800. The EOS 30D I shot with had no IS, so the ability to shoot at f/2 helped ensure a high enough shutter speed and ISO to minimize motion blur. The other blur (a.k.a. "bokeh") is from shallow depth-of-field. The guitar pick-shaped highlights at the upper-right are a result of how off-axis light enters the lens diaphragm. As blurred backgrounds go, I've seen worse. The dual Max Brenner reflections are also pretty cool.

In the first installment of this post I described the main risk of using fast lenses; that because depth-of-field narrows in proportion to the size of the aperture, large apertures reveal just how accurate (or inaccurate) your camera's focusing system is. Some cameras let you calibrate individual lenses, some don't. Some lenses don't need calibration, some do. Suffice it to say that getting consistently sharp results at large apertures puts you on the bleeding edge of today's autofocus technology. You're going to have to risk getting cut if you want to play in this arena. But, at least in my opinion, the rewards are worth it. Here are the main ones:

1. Faster shutter speeds

All other things being equal--that is, the same light level and the same ISO setting--the ability to open the lens wider gives you the ability to increase the shutter speed by a proportionate amount. If you increase the aperture by a stop, say from f/4 to f/2.8, you can increase the shutter speed a stop; for example from 1/30 to 1/60 second. The benefit of a faster shutter speed is that it helps reduce subject motion and camera shake. Image stabilization reduces only camera shake. Combine a wide-aperture lens with a camera that has built-in image stabilization and you've got a winning combination for low-light photography.

2. Lower ISOs

If you're shooting in low light with a camera and lens that don't have image stabilization, you often have no choice but to increase the ISO to get an acceptably fast shutter speed. Increasing the ISO means increasing image noise, no matter how good your camera. The more light you can let into the lens, the less you need to increase the ISO, use a longer shutter speed, or mount the camera on a tripod.

3. More available apertures

The first two options exist because fast lenses have more apertures to choose from than the typical kit zoom. Zoom your 18-55mm f/3.4-5.6 to its maximum focal length and your list of available full-stops is f/5.6, f/8, f/11, f/16 and maybe f/22, most of which are pretty useless indoors without flash. Compare this to a lens with a maximum aperture of f/1.4, which offers all five of the previous ones as well as f/1.4, f/2, f/2.8, and f/4. These larger apertures not only allow faster shutter speeds and lower ISOs, they allow the next item on my list.

This was shot with a Canon 50mm f/1.4 EF at 1/60 second at f/2.8 and ISO 800. It was lit primarily by a portable flash unit bounced off a white wall to my left, so the effective shutter speed was much higher. Despite the shallow depth-of-field, the areas that are sharp are very sharp.

4. Shallow depth-of-field

As I mentioned in my intro, larger apertures reduce depth-of-field (again, all other factors being equal). This can work to your benefit whenever you want to separate your subject from an otherwise distracting background. The degree to which a background is out of focus depends on the relative distance between the background and your subject as well as the focal length of the lens. Regardless, as long as your primary subject is much sharper than the background (or foreground, for that matter) it will literally be clear what you want the viewer to focus on. Depending on what lens you use, the background blur (bokeh) may be attractive in its own right.

5. Lens resolution

There are exceptions of course, but as a rule, fast lenses and especially fast primes become amazingly sharp a stop or two down from maximum aperture. They generally stay that way, from center to edge, all the way down to the point where lens resolution becomes diffraction-limited. Telephotos and tele-zooms can be sharp, center-to-edge, even at maximum aperture. It some cases your sensor is the limiting factor, not the lens. What this means is that with good technique you're assured of getting the maximum quality your camera can deliver. This is not so important if you're only viewing images at screen resolution or making small prints, but if you ever need to crop an image or enlarge to 11x14-inches or more, you'll appreciate every extra drop of lens resolution you can get.

6. Affordability

If you don't already have a fast lens or two in your collection, it won't necessarily cost you a fortune to acquire one. You can find 50mm f/1.8 lenses for less than $200. You might even be able to find one for free, if you don't mind a film camera being attached to it. Prices rise as you start looking for wider apertures, focal lengths wider or shorter than 50mm, or zooms, but if you really need a fast lens for all the reasons I mentioned above, it's still one of the most cost-effective ways there are to improve the quality of your low-light photography. Understand the risks and you'll be ready to reap the rewards.

Comments

[Gavin McLelland]

After I got my Nikon D40 last year, the first lens I bought was the then new Nikon 50mm F1.4G AFS. I was frustrated taking photos indoors with the kits lens and flash. Using this lens has taught me so much about photography, focus, sharpness, DoF, using available light and I have managed to take some photographs I am very proud of.
I would back your recommendation and have strong armed a couple of others into buying a fast lens
Gavin

[John Roias]

I can see we all have needs, styles, and choice of subject matter. I certainly agree with your well written points about fast lenses. But for what I shoot, almost any lens will do. I seldom shoot people or street photography, except family and friends and general scenes. I will say that looking through a fast lens is superior to looking through a slow lens. The difference in brightness is amazing. And the other application I can see is for macro work when you utilize and want bokeh as part of the image. After saying all that, if I can afford it, I will certainly buy the faster lens, especially that 50-135, F2.8.

JMR

[Maureen]

Thanks for the information about calibrating lenses.

I agree with you about the fast lenses. If they are good, the out-of-focus/bokeh areas can look like a painting. They can give a wonderful look to a photograph.

Hope your holidays are happy and wishing you a happy and prosperous New Year!
M.

[Gordon Lewis]

Thanks for the good wishes, Maureen. Happy holidays to you as well.

And just as an afterthought, I think it's worth mentioning that the vast majority of cameras and fast lenses work just fine without calibration. Calibration (a.k.a. fine-focus adjustment) is something to consider only IF valid testing reveals a consistent problem. There are plenty of things about photography to drive us insane without looking for more.

[fortytwenty]

Great post Gordon. I agree with almost everything you've said. Almost. At the start of this second part you say: "Suffice it to say that getting consistently sharp results at large apertures puts you on the bleeding edge of today's autofocus technology. You're going to have to risk getting cut if you want to play in this arena."

Although in the one sense this is true; that is, IF you rely solely on autofocus. However there's another way: manual focus. Combine today's cutting edge camera systems with old-style manual focus techniques which allow ultra- precision focusing and you can't lose. You can shoot wide open with no fear of your lens/camera focus calibration being off. The only room for error is your own Mk.1 eyeball. If that isn't working well enough to manual focus then you aren't going to notice that it's out of focus anyway!.

Seriously, without going on (though I realize the glass of wine I'm enjoying has encouraged me to do this already) I recently acquired a Panasonic GF1 MicroFourThirds camera. While initially stunned by it's ability with it's own f1.7 20mm lens (which is pretty fast itself), i've recently been playing around with it fitted to some super fast legacy lenses. The results are awesome. I had forgotten how amazing the human eye is at focusing. If you're worried that your camera's autofocus won't be up to standard for a super fast prime lens, don't. Get it, manual focus it and you never know, you may just love it. Furthermore, you may just save some money as lenses from the 1980s are going for peanuts on eBay.
That said, thanks for the post Gordon, I really enjoyed it.

[Gordon Lewis]

Manual focusing is a lot easier and more accurate when you use a camera designed with this in mind. Today's AF cameras have focusing screens optimized for brightness rather than precise manual focus. That's partly because so many cameras these days are sold with kit zooms with maximum apertures that range from f/3.5 - f/5.6 and partly because some of the incoming light is siphoned off the to light meter and autofocus system. As a result, it's often difficult to place the plane of focus exactly where you want it to be, especially with fast lenses. Install a screen that's designed for manual focus and it's a different story. For those of you interested in installing a manual focusing screen in your DSLR, visit Katz Eye Optics at www.katzeyeoptics.com.