WHICH EXPOSURE MODE TO USE? Av, Tv, Program, or Manual?

I teach an on-line Fundamentals of Photography Made Easy course for Betterphoto.com, and I get a lot of questions about which exposure modes are best for various situations. Here is my answer to that important question. In reading this, you will find it especially interesting regarding my thoughts on Aperture priority (Av).
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Aperture priority (Av): This is an automatic exposure mode where you set the aperture on the lens and the camera varies the shutter speed according to the light and your ISO.

Use Av mode when the lens aperture is very important. Av is important when shooting subjects that require complete depth of field (or when you specifically want shallow dof). Small apertures like f/22 or f/32 give you maximum depth of field where the foreground and the background are both sharp. You only use Av when SHUTTER SPEED ISN'T IMPORTANT. Assuming you want a tack sharp picture, this last phrase is crucial. This means that you are using a tripod and your subject isn't moving -- such as a landscape, cityscape, architecture, a macro subject where there is no wind, etc. The reason I make this point is because it is very, very easy to use a small lens aperture thinking, 'Oh, now I have lots of depth of field and everything will be sharp', and you forget what's happening to the shutter. If the shutter speed inadvertently gets too slow, your picture will be blurred and you will end up getting the opposite of what you want.

What good is maximum depth of field if the picture isn't sharp?

Therefore, keep in mind that Av can be ‘dangerous’ unless you are on a tripod and your subject is perfectly still. If you want to purposely blur your pictures, such as when shooting moving water, that’s a different story. If you want a completely tack sharp picture and you use Av hand-held, you must always pay attention to what’s happening with the shutter speed. If it gets slower than 1/60th, chances are your images will not be sharp. If you are using a telephoto lens in the 300mm or 400m range, you need a shutter speed at least 1/250th of a second, although 1/500th is better.

The other situation in which you can use Av is when you want the fastest shutter speed possible, given the light and given the ISO. If you set the lens to the largest aperture, such as f/4, then the shutter speed will be as fast as possible. This is what I do when I photograph wildlife with my 500mm f/4 lens. I use Av and set the lens to f/4. I know that this will give me the fastest shutter speed possible to freeze any movements of an animal.

Shutter priority (Tv): This is an automatic exposure mode where you set the shutter speed and the camera automatically varies the lens aperture.

You use Tv when you specifically want a particular shutter speed, such as when you want to blur a dancer or a running horse. You could choose 1/8th of a second, for example. If you are shooting something that moves very fast, like a kid playing soccer, you can select a fast shutter such as 1/500th of a second.

Program mode (P): Program mode automatically varies both the aperture and shutter speed according to the light and the ISO you’ve chosen.

When I am hand-holding the camera, I use Program mode most of the time because it is designed to select the fastest shutter speed possible, minus about 1/3 f/stop. It assumes you are hand-holding the camera and it tries to give you the sharpest picture possible. I take the camera off Program mode when I want a specific depth of field or a specific shutter speed. If, for example, Program is dictating 1/250 at f/5.6 and I want more depth of field, I will switch to Av.

Manual mode (M): Manual mode means that you physically turn the shutter speed and aperture dials to set the camera according to what the in-camera meter tells you is the correct exposure. Many amateur photographers (and some pros) think that this gives you the greatest creativity. Not true. All you are doing is relying on the in-camera meter and doing what it says. What is the difference between manually turning the dials or having the camera do it for you? The answer is … there is no difference. Manual exposure mode slows you down. For fast moving subjects like children, sports, and wildlife, shooting on manual means that you will miss a lot of pictures because you’ll be fiddling with the controls on your camera instead of concentrating on the subject and shooting.

Exposure Compensation: This feature that all digital cameras have allows you to over- or underexpose your pictures in 1/3 f/stop increments. If you are using any of the automatic exposure modes (Tv, Av, or P), this gives you all the creativity you need in varying the exposure according to what you want.