Understanding Aperture – camera fundamentals

Posted on August 8, 2011 by Tim 2 Comments

The shorter the focal length (wider field of view, e.g. 18mm, 35mm, 50mm, —->, 600mm) the greater the DoF. If you shoot a 18mm lens at f/11 pretty much everything from 1-2 meters to infinity will be in focus. You shoot a 600mm lens at f/11 (depending on distance to subject) your DoF may only be a centimeters to a meter. Technically, it is the magnification of the subject that effects DoF. In other words if you got really close to someone and filled your frame with their face with an 18mm lens at any given f-stop you would have the same DoF as you would if you were far away and used a 600mm lens creating the same magnification. But again for ease of explanation I will present it this way since beginners tend to think of lenses on their own.


This scan of an older slide was taken in the Granite mountains of the Mojave National Preserve looking east towards the Providence mountains. It was shot at f/11 on a 20mm lens. Notice how all the elements in the photo are sharp, from the barrel cactus in the foreground to the distant clouds and mountains at the ‘infinity’ focus range. Scenic photography generally tries to maintain as great a depth of field as possible.


On the other hand this black-headed grosbeak was shot at 850mm (600mm lens with a 1.4x teleconverter) at f/7.1 at just under 20 feet away. With such a long lens at a close range the depth of field is very shallow yielding just the head/eye and chest sharp while the rest of the bird gently blurs. The vegetation 10 feet behind the bird, except for context and color, is unrecognizable.

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  • Lyle says:

    Hi Tim,

    I can’t get enough of your work. In fact I have been staring at it at work for far too long. I just read your aperture article and have a question about flash. I’ve been using the 105mm Nikon macro lens and am having trouble with DOF, i.e. not enough of the subject is in focus. Does flash have an effect or am I probably too close and need to back off a little? Thank you

    • Tim says:

      Lyle, flash won’t effect DoF. The distance to subject (more magnification – closer is less DoF) and aperture size (smaller aperture [bigger f/#] the greater the DoF). I suggest putting your Nikon in Aperture priority (A) mode. Then selecting an aperture to get your desired effect. Start with f/11 then go smaller (f/16, f/22) and see what results you get. The flash will give you more light which allows you to shoot those small apertures. Nikon’s CLS (advanced flash lighting meter system) will compensate the power of the flash to give you a shutter speed fast enough to freeze the subject. It gets more technical from here but this is a start.

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