What’s All This About Aperture?

By , December 25, 2013 6:00 pm
Of all the important options we have in photography, aperture selection ranks at or near the top.

Of all the important options we have in photography, aperture selection ranks at or near the top.

When I was a young teenager just learning about photography, I saw the word “aperture” in magazines like Popular Photography, but never heard it spoken out loud. I sounded it out in my head as ape (as in simian) + erture. My dad used to laugh at me about it. By the time I hit high school, though, I was saying it correctly.

I wasn’t using it correctly though, at least not all the time. I could tell just from using the stop-down lever that smaller apertures gave me more depth of field and large apertures made it shallow. But putting them into practice would take years to master.

f/1.8, f/5.6, and f/22.

f/1.8, f/5.6, and f/22.

In an optically-ideal world, one without limitations in budgets or physics, lenses are actually supposed to be their very sharpest “wide open,” meaning at their largest aperture settings. In the real world of photography, though, the truth is that most lenses tend to be their very sharpest at about two f-stops down (smaller) from wide open. A classic example is the ubiquitous 50mm f/1.4 lens. Wide open it will tend to be soft in the corners and littered with various aberrations. Two stops down, f/2.8, though, will make the lens absolutely dazzle with sharpness.

A few lenses, like the vaunted AF-S Nikkor 85mm f/1.4G, or the even more exotic Canon EF 85mm f/1.2L II USM, are designed specifically for use at that huge maximum aperture. Most photographers who use these lenses don’t use them for their low-light capabilities (though there is a dedicated following that does) but for the powerful selective focus ability of these apertures.

I’ve enjoyed the benefits of those big f-stops for years, and recently several of my students have “seen the light” and begin to explore their capabilities. All you have to do to begin to see what a big aperture can do is shoot something with a “kit lens” (like Nikon’s 18-55mm f/3.5-5.6) at 50mm at its largest aperture, then shoot it with a large-aperture 50mm lens at its largest aperture. You don’t have to take my word for it; borrow a 50mm f/1.8 or an 85mm f/1.8 and give it a try. It’s pretty amazing.

Take a look…

50mm at f/16

50mm at f/16

 

50mm at f/1.8

50mm at f/1.8

 

One Response to “What’s All This About Aperture?”

  1. Wil C. Fry says:

    Another thing often skipped when mentioning wide-aperture lenses is — for those of us who use auto-focus — there’s more light available for auto-focusing.

    That kit lens you mentioned has to (at 50mm) autofocus with a narrow f/5.6 aperture, while that nifty-fifty is using a huge f/1.8 (regardless of aperture settings for your image).

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