How to Maximize Your Sharpness

By Chris Walker

Every so often, we stumble across the perfect situation, that confluence of place and time we've been dreaming of for years. The clouds part, sun streams down from above, angels sing. You know what I'm talking about. It's that moment when you see the scene before you and just know it needs to be on your wall. Big. Really big. That's right, distastefully large.

Clyde Butcher, here we come!

You've been waiting for it to happen, so load up that roll of slow, fine-grained negative film you've been carrying just for the occasion. You mount your camera on the tripod, compose the image, maybe make a lens change or adjust your position somewhat. Finally, it looks perfect. And now what... The next steps you take can make the difference between a wonderful enlargement and fuzzy disappointment. What to do, what to do...

First off, set your camera to manual. Advancements in automated functions have made this end of image-making almost foolproof, but they still lack input from the photographer. While "auto" usually makes great prints for sharing, I guarantee you your camera has no idea what size you'd like your final print to be. So don't let your camera make mistakes for you - make them yourself! It's how we learn; make a few shots on auto, if you wish, then use your own intuition to make the real frame.

There are a number of adjustments that can be made to improve image quality one nudge at a time. When used in tandem, they can provide a final negative that's not only capable of significant enlargement, but maintains the feeling of the original scene.

Among the best of these tweaks is the selection of the most appropriate aperture. The diameter of your aperture - the number that's generally called your f-stop - determines not only the amount of light that passes through your lens, but also the foreground/background distance within your image that appears to be in focus. At f-2, the amount of your image that's in focus will be restricted to that on which you've focused. When shooting the Grand Canyon from a ledge, f-2 is enough to get your image acceptably in focus for a small print. But if you were to frame up a cactus six or eight feet from the lens, with the rest of your scene a mile in the distance, at f-2 you'll need to choose which you'd like to be sharp, the foreground or the background.

Shooting at a smaller aperture, such as f-22, would cure the problem of having to choose, especially if you take a moment to check the distances on your lens barrel and focus a third of the way between the nearest and farthest objects. Doing this "shares" the increased depth of field gain from using f-22 throughout your image, at a ratio of 1/3 in front of your point of focus and 2/3 behind it. Although this isn't a bad choice, it's not necessarily the best option.

On getting their first tripod, most photographers start shooting every image stopped all the way down to the minimum aperture - whether the image "needs" it or not. There are a few practical problems that can come with this, ultimately preventing your dream-scene from making an ideal enlargement.

The first problem lies in a slight, overall loss in sharpness. It's easy to see this effect, especially if you wear glasses or contacts. Just take a piece of heavy tinfoil and punch a tiny, round hole in it with a pin. Then strip down to your naked eye and look at a scene through the hole. Virtually everything - at any distance - will be equally sharp! The problem is that none of it will be critically sharp... The effect of using f-22 is much less dramatic, but it's there.

The long-standing rule of thumb for maximum lens sharpness tells us to shoot two stops down from "wide open". This will yield the greatest degree of critical sharpness your lens can offer, but to what avail? Using an f-2 lens at f-4 might yield a spectacularly sharp plane of focus, but it gives you diddley for depth of field. Conversely, setting that same lens at f-22 would certainly yield images with considerable depth of field, but they'd be lacking critical sharpness throughout the image - even on the exact spot where you focused. Test and compromise; it's the only way.

Occasionally we all come across an image that has a near subject and a distant background, both of which you'd like to have in focus, thus requiring a tiny aperture to keep everything appropriately sharp. For general shooting, though, I find that two to three stops open from a lens' minimum aperture is the best compromise for both depth of field and critical sharpness. But remember, critical means critical!!! A 4x6 print won't show you the sharpness lost from having used f-22; that little surprise will come when you get your first 16x20 or 20x24 made, and realize that the entire print appears to be subtly out of focus. Don't stop down farther than what is necessary to adequately cover your subjects; this will yield sharper results in the long run.

The next point of frustration that comes with using small apertures is reciprocity failure. Typically, this only affects folks who use slower, fine-grained films under low light; i.e. it's a problem associated with long exposures. As a rule, when we stop down one stop, we have to slow our shutter speed down one to compensate for the smaller aperture. So, in theory, if your meter tells you to shoot at a half second at f-2, you'd think that could be converted to f-22 by going to 1 second at f-2.8, two seconds at f-4, four seconds at f-5.6, eight seconds at f-8, fifteen seconds at f-11, thirty seconds at f-16, then finally a minute at f-22. This only works in theory.

While most films require different adjustments to compensate for reciprocity effects, problems with this generally begin around a second or two. The first symptom you'll notice is that your images will be underexposed. After that, closer inspection will show that the color is off - while highlights often go a bit magenta, shadows tend to go a bit green. And since green and magenta are opposites, so if you try to get highlights printed normally, your shadows can become unpleasantly green, and visa versa.

A variety of adjustments comprise the ounce of prevention for this malady, starting with either selecting a film that has better reciprocity characteristics; a slightly faster film so your exposure won't have to be so long; or sacrificing an f-stop in depth of field so you can cut your exposure time in half, thereby creating fewer problems for yourself in post production. As far as postproduction goes, the pound of cure comes through digitizing your negative so that highlights and shadows can be adjusted individually; if done well enough to provide the resolution and file size adequate for making extreme enlargements, which would probably require a drum scan, this option is quite costly - and that's before you've paid the technician's fee for making the actual adjustments.

So think your way through important images, make your decisions intentionally, and when all else fails, hope to get lucky once in a while. Most importantly, keep at it! As landscape photographer John Sexton says, the more he practices, the luckier he gets.