Look sharp, be sharp: Taking sharp photos9/12/2011 07:27:00 PM
Beginning photographers often complain that their photos aren't "sharp" and they want to know what they need to do to make the...
Beginning photographers often complain that their photos aren't "sharp" and they want to know what they need to do to make their pictures sharper.
Now the first thing I want to say is, sharpness is overrated as a photographic virtue. I mean, obviously, most of us don't want to take blurry photos. But sharpness doesn't make a photo good. A great photo has an interesting subject, an artistic and pleasing (or perhaps challenging) composition, good lighting, intriguing colors and contrast, and so on. Sharpness is nice, but let's not make a fetish of it.
That said, it's not so simple as "do X and your pictures will be sharp". What we call "sharpness" in photos is an effect that can be reduced or harmed by several different factors. I'm going to limit myself to five important types of problems with sharpness:
- those due to inadequacies in the lens;
- those due to faulty focus;
- those due to subject movement combined with a shutter speed too slow to compensate;
- those due to camera movement (or camera shake);
- and finally, the basic nature of digital capture.
This list is not exhaustive. I'm just trying to cover the most important factors. I'll talk about them one by one.
Want to take better, sharper photos? One thing you should do is make sure you're using a good lens. And when I think of "bad" lenses, I'm not thinking of the lens in your iPhone, I'm thinking of those consumer-level $280 lenses that you may have lying around. Actually there are very few truly bad lenses these days. And the price of a lens isn't an absolute guarantee of its quality. The Pentax DA 16-45 f/4 is a terrific lens and comparatively inexpensive (under $400 on 9/12/11 from Amazon). The Sony DT/SAM lenses are also much better than their price tag might suggest, in part because Sony cut corners lens on the housing (these are plastic lenses) rather than in the glass. But in general, cheap lenses don't resolve detail as well as more expensive lenses, and if you can't resolve detail well, you can't achieve serious sharpness.
But I want to add something about lenses. This isn't a simple issue, certainly not as simple as saying "Spend $1200 on a lens and you'll get sharp photos." For one thing, the lens is only one of the factors in taking sharp photos; some of the others are discussed in the following sections. But it's also the case that the difference between a $1200 and (say) a lens that costs only $600, is almost certainly not as great as the difference between a $600 lens and a $300 lens. In other words, the more you pay, the less you get in the way of improvement. (This is true of cameras as well.) Anyway, some of the weakness in a lens can be compensated for in software with a sharpening tool; see below. But sharpening on the computer produces a good result only if the original is pretty sharp to start with. So, to take sharp photos, you don't have to have a great lens. But you do have to have a good one.
This is a much more complicated factor than you might think. It should be fairly obvious that a picture has to be in focus to be sharp. But what is optimal focus? How do you achieve it, or to put the question in a negative way, what might prevent you from achieving optimal focus?
Optimal focus means a satisfactory or pleasing amount of sharpness where you want it. Not everything has to be in sharp focus, in fact, it's a paradox of photography that, when parts of the photo are out of focus, the parts that are in focus are emphasized. That's why portrait photographers like the shallow depth of field achieved with large apertures, long focal lengths and/or close focusing (and if you want to spend the money, larger sensor cameras). We often like to focus tightly on the subject's eyes, but it's not a rule. Given the right subject, you just might want to focus on the nose. For example, there's nothing wrong with the focus in this photo.
Now, what are the different types of problems you can have with focus?
Autofocus doesn't work very well when what you want to focus on is behind something that can confuse the camera. This might happen if you're photographing an animal at the zoo behind a fence. In this case, you almost always have to switch to manual focus.
Autofocus also has problems when the focal point doesn't have much contrast. This might happen if you're trying to photograph a blank white wall. Try focusing on the edge of something, something with some contrast in it. This problem is exacerbated when the light is low.
Another problem with autofocus can occur when you focus and recompose, that is, when you focus on an element of the photo that isn't right in the center, and then recompose your shot. This is something many photographers do quite often; I confess I do it myself, although I am aware of the problems with this technique and I use it with caution. The problem is, if you are pretty close to the focal plane (the part of the subject you want to be in focus), then when you recompose, you may change the distance between the camera and your desired focal point enough to throw that target out of focus. You should follow this link to find out why focus-recompose sucks. I imagine that the focus or sharpness problems of a fair percentage of photos can be explained by focus-recompose.
If you have a lens that is supposed to be very good and feel that you never get good, sharp photos from it, and if you use autofocus exclusively, be aware of the possibility that your lens may be out of adjustment for autofocus, that is, it may be front-focusing (actually focusing a little in front of the place you want it to focus on) or back-focusing (the reverse of front-focusing). Google these topics for more info. These problems are not common, but they do occur. One of the advantages of manual focusing is that it isn't affected by front or back-focusing. If the lens is good, you should be able to achieve clear, sharp focus if you do it manually.
Finally, there's a host of other difficult issues that I really don't want to talk about. Don't use f/2.8 to shoot a group portrait from 8 feet away or some of the people in the shot probably aren't going to be in focus, when they should be. If your camera offers you a choice between phase-detect and contrast autofocus, look into the difference so you understand the pros and cons of each. Understand that your camera can't autofocus well in very low light — and you won't be able to focus manually in low light either, because in low light, neither you nor your camera can see very well. Shooting at higher ISO (because light is low) inevitably means some loss of detail and may make an impact on sharpness.
Anyway, the autofocus systems on cameras are not all created equal, far from it. The number and type of autofocus points in the camera make a difference. So does the lens (as a means of delivering info to the camera for the camera to autofocus on), the type of light, and other factors. Since my purpose here isn't to talk you (or myself) into buying a new camera with potentially better autofocus, let's just say that it's important to know what you can expect from your camera when you use autofocus.
If you have time for it, manual focus can be better, that is, it can sometimes achieve sharper, more precise focus. These days, I use manual focus quite a bit for portraits with adult subjects, not so often for candids of active children (not to mention sports photography, which I don't do much of any more). But it's worth remembering that we're all spoiled by the automatic features on our cameras. It's good to shoot in M mode regularly and it's good to use manual focus regularly, just to "stay in shape". Once upon time, manual focus was all there was, and photographers managed to take great photos. I increasingly use manual focus with my Sony DSLRs because of the feature that lets me fine-tune manual focus in live view.
The first two causes of unsharp photos — bad or mediocre lenses and focusing problems — are things that some photographers forget when thinking about sharpness, but they are of basic importance. Now, I get to the first of the factors that every knowledgeable photographer does think about in connection with unsharp photos, or at least should think about: subject movement.
In a word, it's hard to take a sharp photo of a moving subject like a rodeo cowboy riding a bull, or a child squirming in his mother's arms. In the early days of photography, it was impossible. Photographic subjects had to be still while their picture was being taken, sometimes for lengths of time that today seem impossible (30 seconds or longer). Portrait photographers used some equipment that looks pretty kinky today to hold subjects' heads still while they posed. But those old photographers often got extraordinarily sharp photos.
Today it's not impossible to get a sharp photo of a moving subject, but it can be difficult. The basic trick is to make sure that your shutter speed is fast enough to freeze the action. The photo above was taken at 1/4th of a second — way too slow for the wriggling boy. That shot probably needed at least 1/160th second. If you're photographing a school soccer game in good daylight, you might need 1/500th second for some shots. It's hard to recommend specific shutter speeds, because there are too many variables. But to freeze the movement, the shutter needs to be fast enough.
Getting the shutter speed fast enough to freeze the action only works, of course, if the subject is in focus. In the picture above, subject movement is the most obvious problem. But the truth is, the camera hadn't really finished focusing when I pressed the shutter; so even if the mother and her son had been frozen still, the picture still wouldn't have been sharp, because it would have been out of focus. If you're photographing subjects that are moving from right to left or vice versa while remaining roughly the same distance from you, it's easier to achieve focus, then you just need a fast shutter to stop the movement. If the subject is moving toward you or away from you, especially if it's relatively close, you may have trouble keeping the subject in focus. Your camera's continuous focus option should help in this situation.
Note that, at least now and then, the subject may be moving relative to the background but fairly still relative to itself. In this case you may want to pan the camera with a slower shutter speed, to get your subject into sharp focus but blur the background. I talked about this at some length a year ago, in a post titled "Horses in motion."
Now, subject movement isn't just a problem with children, animals, athletes. It can also be a problem in macro photography, where you photograph flowers or insects close up. In macro photography, because you are so close to your subject, you often have very little depth of field. And if you're shooting outdoors, and there's even the tinest whisper of a breeze, your subject may be moved around just enough to wreck focus or sharpness. You can't solve this problem by increasing the shutter speed, because the problem in this case is that the subject is moving out of the focal plane. The solution here is to wait for the breeze to go away, or get lucky.
Using flash can help you get sharper photos. Even when the available light is sufficient for a nominally good exposure, it may make sense to use flash, partly because more light may add to the clarity of the shot, but also because the flash can freeze the action even if the shutter is much slower. Say you're shooting a birthday party. You might want to "drag the shutter," that is, drop your shutter speed below the camera's flash sync speed (usually 1/160th second, or 1/180th second or 1/250th second). Dragging the shutter lets the available light help with the exposure and can give flash photos a more natural look. But the flash itself illuminates the scene brightly for about 1/1000th second, and at least if you're using the flash in TTL metering mode, the camera will be exposing for the flash rather than the available light. The very brief burst of light from the flash will freeze the action while the available light that reaches the sensor during the rest of the time the shutter remains open will simply fill in some of the shadows in the picture.
Camera movement (also known as "camera shake")
Subject movement can cause problems with sharpness, but an even more serious problem is camera movement or camera shake. You can take an unsharp photo of a building or a mountain, if you jiggle the camera. Camera shake is a major cause of unsharp photos. The effects of camera shake become more pronounced as distance from the subject increases. This is very like the problem of shooting a rifle: the farther away the target, the steadier you need to hold the rifle if you hope to hit your target.
It's important to develop good camera holding technique and equally important to learn how to squeeze the shutter without causing the camera to move. But apart from holding the camera properly, there are some things that can help you get sharp photos.
Here's a photo taken handheld at 300mm, from a distance of close to 20 feet. My Sony A550's SSS ("Super Steady Shot") image stabilization feature was turned off. You can click on the photo to view a larger version, where the photo's lack of sharpness will be more apparent.
The next photo was taken with SSS image stabilization enabled. Although I have pretty good camera-holding technique and I squeeze the shutter very smoothly, human beings are not made of stone and there is always a small degree of camera movement in any handheld shot. The image stabilization works to compensate for that slight movement and it does a pretty good job. The next photo is considerably sharper; again click the photo to view the larger version where the improvement will be easier to see.
Sony and Pentax DSLRs (and Sony DSLTs) have image stabilization built into the body, so you get the advantage of it no matter what lens you are using. Canon and Nikon DSLRs, on the other hand, do not have body-based image stabilization; instead, you can spend extra to buy image stabilized lenses. Whether it's provided in the body or the lens, image stabilization can help your images be sharper. I use Sony cameras in part because I never want to be without image stabilization.
However, image stabilization compensating for camera shake isn't as good as getting rid of camera shake, which you can do by putting the camera on a tripod. Here's a third shot, with the camera on the tripod. To minimize camera movement even further, I used an electronic remote to trip the shutter, so I didn't have to touch the camera directly.
This is easily the sharpest of the three shots.
If I could shoot with my camera on a tripod all the time, I would. By eliminating camera movement almost completely (at least if you have a good tripod and know how to use it) the tripod gives you the best chance to get a really sharp photo. But of course, most of us can't or won't carry a tripod with us everywhere, and when the use of a tripod is inconvenient, impractical or simply impossible, then image stabilization is the next best thing.
Addendum 9/14/11. I mention above two ways to fight the de-sharpening effects of camera shake, namely, the modern, high-tech feature of imagine stabilization or the classic technique of placing the camera on a tripod. There is a third semi-classic technique that deserves mention: increasing the shutter speed. I mentioned shutter speed as a way of dealing with subject movement, but it helps minimize the negative effects of camera movement as well. The classic rule of thumb is use a shutter speed that is equal to or faster than the reciprocal of the full-frame equivalent of your focal length. If the focal length is 300mm, the reciprocal is 1/300; but note that the rule of thumb requires that you adjust for your camera's sensor size or "crop factor". On a Sony APS-C sensor DSLR like the Alpha A550 that I used for the shots of the globe above, the rule would call for using a shutter of speed of at least 1/450th sec when shooting at 300mm, that is, the shutter speed should be at least as fast as focal length x 1.5. If you don't have image stabilization or a tripod, the rule is pretty useful. I took two shots, handheld, at 1/500th sec, one with my camera's image stabilization feature enabled, the other with the feature turned off. I can't see the difference. If you do have image stabilization enabled, you may be able to use a slower shutter speed than the rule of thumb calls for.
The nature of digital capture
The final consideration — the nature of digital capture — is one that I'm going to mention only briefly. The basic idea is that, because digital capture stores images as arrays of discrete pixels, there is a degree of "distortion" inevitable in digital capture and digital images can almost always benefit from some amount of sharpening after the fact. Undoubtedly the best book on this subject is Fraser and Schewe's Real World Image Sharpening, and I refer you to it, if you are serious about the subject of sharpening. Fraser and Schewe explain the why as well as the how, and in detail.
I simply want to reiterate that sharpening on your computer can't really fix problems caused by the previous four factors. If you shoot with a lousy lens, if you haven't focused your image well, if the subject is moving too fast for the shutter speed, and/or if the camera isn't stable at the moment you press the shutter, then there's not a lot you'll be able to do on the computer to make the image sharp. The sharpening feature in your processing software (known in Photoshop as "unsharp mask") really ought to be called "increase sharpness" rather than simply "sharpen." If the photo is a blurry mess to start with, your best bet is to delete it and take another shot.