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Tuesday, April 24, 2012

Prime Time

Once mostly cast aside in favor of high-tech zoom lenses, primes, or single-focal-length lenses, are making a serious comeback with pro photographers

This Article Features Photo Zoom

Canon EF 300mm ƒ/2.8L IS II USM; Canon EF 50mm ƒ/1.2L USM; Canon EF 85mm ƒ/1.2L II USM
Like just about every lens, a prime is at its sharpest a few stops down from wide open. On a fast pro zoom, this sweet spot is usually around ƒ/8 or ƒ/11. On a prime lens with a maximum aperture of ƒ/1.4, the sweet spot can be ƒ/4. The key advantage here is that you can be shooting with the lens at its sharpest, while at the same time maintaining a narrow depth of field and smooth bokeh.

Depth-Of-Field Control. Bokeh is a term that has recently become ubiquitous among photographers, mostly in the wake of DSLR filmmaking. It was the bokeh characteristics—and seeing that bokeh in HD video footage—that really started the resurgence of prime lenses for DSLR shooters. The game change that began with Vincent Laforet's Reverie continues today. Reverie didn't invent bokeh, but the short movie brought the look of limited depth of field and smooth out-of-focus areas to the forefront of our awareness.

Bokeh is an aesthetic element of a photograph, so it's hard to quantify. It refers to how out-of-focus areas look, and we usually notice the bokeh most in out-of-focus highlights. This is where lens aberrations become quite visible. Also, it's where you actually can see how the number of iris blades will shape the aperture. Lenses that do a good job with bokeh tend to have a minimum of aberrations and also have irises that are mostly symmetrical at all ƒ-stops.

As bokeh has become more of an industry buzz word, and with more and more people shooting high-end HD video with DSLRs for the "cinematic look," newer prime lenses are being designed specifically with the bokeh in mind. Can a zoom lens give you a good bokeh? Of course, but zooms are more prone to aberrations, and the aberrations manifest to greater or lesser degrees at different points along the zoom range.

Should You Unload Your Zooms?
With all of the interest in prime lenses and considering the advantages we've outlined here, is it time to unload your zooms and replace them all with primes? That's not what we're suggesting. As zoom lenses came to dominate the market, however, prime lenses took a back seat for a long while. It's time to take another look and give primes a chance.

Apples & Oranges?
As you're contemplating the benefits of a prime lens, one thing that can get lost is the camera. When film was the medium of choice, the finest-grain emulsions were used to evaluate the lens. In the digital age, the fact that image sensors are a variable has been forgotten at times. Some websites with chart comparisons do an especially good job of raising awareness of this. Anytime you're comparing lenses, don't forget to take the camera into account, or you'll be comparing apples and oranges to at least some degree.


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