Position yourself outside somewhere about 3 feet from a person or large object. Make sure your subject is 50 or more feet from the background. Using a tripod, or just taking care to frame your subject in a similar way, make a series of exposures to see how depth of field works:
- Put your camera on manual and set the ISO to 200.
- Starting at the widest lens opening ( which is the lowest number your lens has, e.g. f4 ) set your zoom lens: Nikon users – 35 mm and Canon users 28mm. Now determine the shutter speed needed to make a correct exposure. The resulting image should look right on the back of your camera, not too light and not too dark.
- For your next exposure, adjust your aperture down to the next full stop. For instance, if your widest aperture is f4, then for your 2nd exposure go to f5.6. To obtain the same exposure, you will need to decrease your shutter speed by one stop (aka unit of exposure). So if you were at 250th of a second, you’ll need to go to 125 to keep the exposure the same. Assuming you correctly follow these instructions, your first and second exposures will both look the same, ie not lighter or darker. If you forget to change your shutter speed, your second exposure will look darker than your first.
- Continue on making exposures, each time closing down your f stop one full unit of exposure and decreasing your shutter speed by one unit.
- When you have traveled the full range of f stops your lens has, you should have a series images that have the same exposure (assuming clouds or night didn’t come and reduce the light during your experiment). Notice how your back ground comes progressively into focus as you stop down your lens. You may also notice that camera shake creeps in, blurring your images as your have to hand hold at slower shutter speeds. Understanding control of depth of field through adjusting aperture is a fundamental, practical and artistic tool, unique to the photographic process.