Keeping it Sharp (part 1)

PhotoNetCast – Photography podcast

We’ve been promising it for a while but this post is the first in an occasional series devoted to photography technique. We would really appreciate your suggestions on further articles that you would like to read in this series.

Aside from a few isolated creative cases, photographers strive to ensure that their images are as sharp as possible in the areas that are supposed to be sharp. When an image falls short, we are often quick to blame poor equipment but, if we are going to be honest with ourselves, we should realize that the vast majority of focus problems are caused not by a cheap kit lens but by “user error”. This article and the one which follows, aim to help you work through the kinds of problem which can reduce sharpness in your pictures and which can be fixed without spending thousands on new lenses.

Before delving in, we should remember that your definition of whether or not a photo is sharp will vary a lot depending upon what you are going to do with it. If you print nothing larger than 6″x4″ or use only low resolution versions of your images on a web site, you will be a lot less likely to notice an unsharp image than if you are producing 36″x24″ prints. The larger your output, the more careful you must be to nail the focus exactly where you want it.

Stabilizing The Camera

Most problems that appear as poor focus are likely due not to lens focusing at all but are caused by camera movement during the exposure (or “camera shake”). A slight movement of the camera is all it takes to blur those eyelashes in an otherwise perfect portrait or turn the leaves on the trees in your landscape into green mush. The problem of camera movement is magnified with longer lenses where a small angle change in the camera translates into a large positional change in the image you are capturing. Conversely, a significantly larger movement is required to produce equivalent levels of image blur when using a wide angle lens.

The most obvious way to prevent camera movement is to lock the camera down hard using a sturdy tripod. While this is the best option, carrying a tripod is unlikely to be practical in many situations but there are several other things you can do to reduce camera shake. The first of these is to hold your camera properly – be your own tripod and support the weight of the camera in a way that is comfortable for you and as stable as possible. The position of your right hand is generally fixed by the camera controls – grip the right side of the camera tightly. Your left hand, however, has a lot more choice and this tends to be where the problem lies.

I was recently at a sporting event and watched an amateur photographer hold a 300mm lens with his hand above the lens barrel. Aside from the fact that this must have been rather uncomfortable, it was also a very unstable way to support a heavy lens (or any lens, for that matter)! Holding your left hand underneath the lens offers a far more stable platform and tucking your elbows in against your sides helps even more. While doing this, keep your feet apart and, if you have the option, brace yourself against something solid – a wall, a tree, a fencepost – to further reduce the likelihood of you moving during the critical hundredth of a second or so that the shutter will be open.

One of the masters of the genre produced a video a while ago that describes what I am talking about here. Joe McNally is a left-eyed shooter so his camera grip technique won’t work for most of us but do watch his video since it contains great information even for those of us who clamp our right eye to the viewfinder.

Even when you are in the fortunate position of being able to shoot from a tripod there are a couple more things you can do to ensure ultimate camera stability. Firstly, to minimise your need to touch the camera and possibly jolt it, use a cable release or, if you don’t have one, set the self timer so that your hand is away from the camera when the shutter fires. Secondly, if your camera has the option, use Mirror Lock Up or Exposure Delay (a Nikon feature which delays the shutter release for a second after the mirror is raised) to reduce vibration caused by the DSLR’s mirror moving. This may sound nitpicky but it can make a noticeable difference if you are producing really large prints.

Shutter Speed Choice

Having fixed problems associated with stabilizing the camera, another question often comes to mind. Just how slow a shutter speed can I use and still get sharp images when I’m hand-holding a camera? I know one professional photographer who claims to be able to get decently sharp, handheld exposures with a wide angle lens when shooting with a half second shutter speed but, for the rest of us, there is a useful rule of thumb. Don’t try to handhold a shot if the shutter speed will be any slower than 1/(focal length). For example, if I’m shooting with a 24mm lens, I should be able to handhold it successfully at shutter speeds shorter than 1/24 second. If, however, I change to a 300mm, I must keep my shutter speed shorter than 1/300 to ensure sharpness. Different individuals obviously have different abilities here but this makes a pretty good starting point for most people.

I still use this rule of thumb today but I can now bend it if I’m shooting with a Vibration Reduction (VR) or Image Stabilization (IS) lens. These lenses include special optics that sense vibration or movement and cancel it out automatically. Most claim something between 2 and 4 stops of improvement over a non stabilized lens of similar focal length, so, using one of these and assuming a conservative 2 stop improvement, I can shoot at a shutter speed 4 times slower than the rule of thumb would dictate and expect to get a shot of similar sharpness. Taking the 300mm example again, without VR, I should keep my shutter speed shorter than 1/300. With the 2 stop improvement I get with VR, however, I can move this limit to 1/75 second (1/150 is 1 stop down from 1/300, 1/75 is 2 stops down) and still expect a sharp shot. I must admit to having been skeptical of this but, on trying out my Nikon 70-300mm VR lens at the 300mm end, I was delighted to find that I can indeed get images whose sharpness I am happy with when hand-holding at 1/30 second.

The previous rules do make one assumption that you also need to consider. Regardless of how well you handhold and how fast your shutter speed is, if your subject is moving and the camera is fixed, the longer the shutter speed, the less sharp the subject will be. In these cases, you would need to move the camera during the exposure (pan) to track the subject position but that’s a subject for another article.

In part 2 we’ll consider how your choice of aperture can affect overall sharpness and discuss the use of your camera’s autofocus system to ensure that you get the sharpest focus in exactly the right place.