Tack-Sharp Images – Part 2:
Good Shooting Technique – Aperture Selection and Exposure Control

In the last column I coined an acronym for how to maximize the stability of your tripod: SMART. If you can’t remember what each letter stands for or just want a quick review, click here. I believe shooting with a sturdy tripod is critical to maximizing image sharpness, so it’s a great idea to review tripod use techniques frequently. In this and the next few articles, we’re going to discuss three areas where sound shooting techniques will help maximize your image sharpness.

Before we dive in, allow me to digress a bit. What exactly do I mean by “tack sharp?” For me it means that everything in the image that should be crisp and detailed is. I assert that you’ll know it when you see it. If your technique is correct, then the image will look “spot on.” If not, then it will be fuzzy, confused or blase.   Keep this in mind as we now examine various techniques for maximizing image sharpness that I will lump into three categories: Aperture Selection & Exposure Control; Composition; and, Trigger Pull. Viola! We have another snappy acronym: ACT for sharper images!!

Aperture Selection and Exposure Control
For most Landscape images, our mind wants to see everything from the foreground to the background in crisp focus because the image in its entirety is the subject. Portraits/Close-ups often demand the subject to pop in sharp relief against soft surroundings so the viewer can tune out everything else. Let’s look at techniques for each of these.

1. Landscapes:

1. Manually Expose: When I shoot Landscapes, I almost always shoot in manual exposure mode to give me full conscious control over aperture and shutter speed. If the light is changing rapidly and unpredictably, I might force myself to use aperture priority mode, but usually I’ll have plenty of time to make deliberate decisions using manual exposure mode. I also shut off the auto-focus.
2. Set Low ISO: I always start with the lowest ISO possible. If presented with moving subject matter, I may bump the ISO up to allow for higher shutter speeds, but I try to avoid this whenever possible. If the wind is blowing and there is a waving flower in the foreground I want to freeze, I’ll usually try to wait it out before increasing the ISO setting. Camera technologies are improving all the time and higher ISO settings now yield much less noise/grain than before, but if you’re trying to squeeze every last ounce of sharpness out of your gear, then the lower the ISO, the better.
3. Use Small Aperture: Let’s assume my goal is to make everything in the image sharp, front to back and side to side. One way is to make a composited image from a series of images all shot from a fixed position (using a tripod, of course) but with varying focus points and then stitching the images together in the computer using software such as HeliconSoft’s Helicon FocusTM.  This is particularly useful for macro photography, but for most Landscapes we can simply stop the aperture down sufficiently to maximize depth of field.

Series 1 (Small stones) f20 (left) vs. f8 (right): Shot at 40mm focal length. The focus point is at the center of the image, approximately 7 feet from the camera. It may be difficult to tell the difference in sharpness from the small images, but in the 100% enlargements it is clear that the image shot at f8 is clearly out of focus and blurry in the background area versus the one shot at f20.
1) f20@1/25sec; ISO 100; focal length=40mm	2) f8@1/160sec; ISO 100; focal length=40mm
RRS Equipment used: BH-55 LR, Canon 1D Mk III, 24-105mm, f4.0

How do I determine which aperture is small enough to give me adequate depth of field?  It depends on which lens I’m shooting with (wide-angles have greater depth of field) but if I’m shooting with 35mm-sized gear, I’ll usually start at f16 and adjust from there. “But wait, isn’t the sweet spot of the lens always f8, as in ‘f8 and be there’?” you ask. Well yes, but in my experience when it comes to apparent sharpness of a Landscape image, greater depth of field (very small apertures) trumps optimal lens resolution settings (usually in the middle of the aperture range). When the key subject matter includes foreground and background elements, it doesn’t matter how many line pairs the lens is capable of resolving if any element is out of focus – it just looks fuzzy.  Having said that, try to stay at least one stop away from the minimum f-stop of the lens.

1. Focus Point: Start by setting the focus point at about ¼ of the distance between the closest foreground element and the furthest background element. If the closest element is relatively close and the furthest element is very far away (infinity focus) then the focus point will be significantly closer than ¼ the distance from the foreground element to the background element. If your camera has a depth of field preview feature, use it. However, when stopping down to small apertures the viewfinder may get too dark to tell what’s in focus and what isn’t. Thank heavens for digital camera LCD review screens! Simply take a test shot and then zoom in to review if everything’s in focus.  One or more elements within the Landscape will demand a bit more attention. Make sure to check that these elements are sharp.

2. Portraits/Close-ups

This category includes individual or tight groups of human, animal, plant or any subject matter that demands the viewers’ focused attention. Everything else in the image serves only to highlight the subject. In this situation, we typically prefer to see the subject in sharp focus while the rest of the image is soft/non-distracting. This differs from images that portray the subject-in-environment when we want to examine the surroundings of the key subject with equal or nearly equal importance. Subject-in-environment images are really just Landscapes from a technical point of view.

This type of image lends its creator an opportunity to do something the viewer would otherwise not be able to do well in the natural world. If you think about it, as long as our vision is good or properly corrected, we see everything one point at a time in perfect focus. But with a Portrait image, you have the power to throw everything out of focus except the subject. How cool is that? To maximize this effect, do the following:

1. Pick the Subject: Remember, our eye focuses on one point at a time. Choose the one point on the subject that you want to draw attention to and make certain that point is tack-sharp. For animals of all types (including bugs and humans) the center of interest naturally is the eye of the subject. If the eye is in the image and in focus, it won’t matter to the viewer so much if the whiskers are fuzzy; the viewer will make an initial connection with your image 99% of the time. Conversely, the opposite is true. If the subject is a flower or an inanimate object, pick a specific point that demands your attention and focus on that.
2. Isolate the Subject: More often than not, I shoot Portraits with a medium to long telephoto lens because the narrower the field of view, the easier it is to pick a background behind the subject that I know will be out of focus and/or non-distracting. You’ll need to move your camera position around till you find the right combination. Don’t be afraid to lie down on the ground or get at eye-level with your subject.
3. Manually Expose: If given the time or uniform lighting situations, I shoot in manual exposure mode, just as for Landscapes. If the subject is moving in and out of differing light, as with a flying bird, I’ll use aperture priority as per “d” below and be sure the ISO is set to yield proper exposure.
4. Use Large Aperture: One great reason for buying the largest f-stop lenses you can afford is that you can do a better job of isolating the subject with a large aperture. Telephoto lenses have shallower depth of field and an f-stop of 5.6 or wider usually does a nice job. With an f2.8 or f4.0 maximum aperture lens, you can shoot at f4 or f5.6 and still be close to the lens’ sweet-spot.

   Series 3 (Lyon) Shot at 180 mm focal length.

   1) f3.5@1/250sec; ISO100; focal length:180mm

   
   
   
5. Set ISO: Low for static subjects; higher for moving subjects. For action shots, I usually want to freeze the subject, which requires fast shutter speeds and higher ISO settings. If you’re after “tack-sharp” remember that the higher resolution/finer grain gained by a low ISO is meaningless if the subject is blurred. In this case, a high ISO yielding a frozen subject trumps any resolution benefits of low ISO.

Next issue we’ll look at how carefully manipulating the composition can aid in the overall sharpness of the image and give a few tips for minimizing shutter release-induced vibration.

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Article written by
Joe Johnson
RRS Owner