By Harold Merton, A.P.

Depth of field or depth of focus comes into play when we focus on a subject in our picture. It is controlled by the aperture.

Most good cameras have apertures that can be adjusted to allow more or less light to strike the film.

The aperture, or f stop as they are also known, will range from perhaps f22 for a very small opening to perhaps f2 for a large opening.A standard scale is used by camera manufacturers throughout the world so you can be relatively sure that an aperture of f8 will allow the same amount of light into the camera no matter what brand of camera you own.

Depth of field is used by serious amateur photogrpahers and professionals as a way of controlling their picture results and it can be a very useful tool.

The basic rule is “the smaller the aperture the more depth there is in your picture”. By small the aperture we mean a small opening not a small number because the opening for f22 is much smaller than the opening forf2.

When you move from f22 to the next largest opening - f16, then you double the amount of light that enters the camera. If you move from f16to the next largest again (f11) then you double the light again so that you have four times as much light as at f22.

You use the aperture you select with the proper shutter speed to give you the combination for correct exposure.

In most cases there are several combinations of aperture and shutter speed that will give you the same exposure.

Normally a person picks either shutter speed or aperture as their priority. Then they adjust the other to get the proper amount of light.

For example if I want to stop action in a children’s race I would pick my shutter speed as priority. Lets use an example of 1/500th of a second. I then move my aperture control until my camera light meter indicates I have hit the proper exposure. Let’s say that it is at f11.

Now if I were to move my shutter speed to f16 (which is one f stopsmaller) I would cut the light in half. However if I changed my shutterspeed to 1/250th (which means it is open for twice as long a time) then I would double the amount of light I have, putting me back at the proper exposure.

You can see that by changing either the aperture one way and the shutter speed the other way, I can in fact have the proper exposure with several combinations.

Now lets look at apertures again.

The smallest apertures (f16-f22) will give the most amount of depth in your picture. Sometimes people don’t understand what I mean by depth. Here’s an explanation.

If you were focusing on a picket fence that was running away from your camera in your picture then there would be a certain number of pickets that would be in focus and some that were out of focus.

Lets say we focus at the picket that was 10 feet from the camera. If we set our camera at f16 then the pickets from about 6 feet to about 20 feet would be sharp or in focus. If however we focused at the same 10 foot mark but used an aperture of f4 then from about 9 feet to about 13 feet would be in focus. If we used an aperture of f2 then even less would be in focus. If we used an aperture of f22 then everything from about 6 feet to infinity would be sharp.

As you see you can use the aperture to control what is sharp in your picture and what is not.

Now lets get back to that problem of having undesirable things in your background showing up in your pictures.

If that happens obviously you are using a very small aperature because small apertures give the greatest depth of focus. If on the other hand you shot that picture with a smaller aperture then the things in the background would be out of focus and being was out of focus renders them indistinguishable.

The object here is to have you consider aperature settings when you are making your pictures. If you want everything in focus use a small aperature but if you want selective focus then use a large aperture. Remember you still have to adjust your shutter speed so that you have proper exposure and sometimes you can’t use the aperture you want simply because there would be too much light or too little light.

If you are on a beach in bright sunlight using ASA/ISO 200 film then you won’t be able to use f2 because there is just too much light but you could probably use f5.f or f8.

Where you are going to make pictures is a consideration that you make when you decide what ASA/ISO to use. If you are going to shoot available light pictures at a concert then 400 ASA/ISO would be acceptable but if you are going to make pictues on the beach in the summer time then 100ASA/ISO would be better.

There’s something for you to consider when making pictures. Think about the aperture you want to use and change it to give yourself the result you want in your final print.

Good shooting!

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