All around lenses

Started Jun 26, 2012 | Discussions thread
mosswings Veteran Member • Posts: 8,064
Re: All around lenses

Allan martin wrote:

Okay, the 17-70 is out then.

I just have to make up my mind about the sigma 17-50.

On one side there's the wider aperture and more speed. (is that it?)

On the other one there's the range. (what else?)

Speed and aperture are two words for the same thing. A "fast" lens has an aperture f2.8 or wider, roughly speaking.

What you are really buying with a wide-maximum-aperture lens is significantly improved optical quality over a consumer zoom like the 18-105. This improvement is purchased at the inevitable cost of zoom range. Study the market and you'll find that the best, most well regarded lenses have zoom ranges less than 3:1, and as you go to the ultrawide range that zoom range shrinks even more.

The quality that these lenses embody is not easily described by gross specifications such as aperture and zoom range. That takes more subtle performance measurements like MTF charts, and, ultimately, actual use, because lens designers can control many other factors that affect the scene rendering capability of the lens (qualities such as color balance, micro and macro-contrast, flare susceptibility, and out-of-focus feature characteristics - the mysterious "bokeh").

While it's possible to design a really high optical quality slower lens, you wouldn't likely want to pay for it because it wouldn't offer you enough for your money.

A general rule of thumb is that lens perform at their best when stopped down 1 or 2 stops from their widest aperture. Therefore, an f2.8 lens, in addition to gathering lots more light when you need it, will at f4 exceed the optical quality of an f4 consumer zoom. But by f8 the differences diminish, and today's consumer zoom quality is such that the differences are much less than in years past.

This zoom range-speed-quality formula reaches its logical end in the prime lens. These are simpler lenses with the least possible compromise in optical quality. But again, the best contemporary zooms are very competitive with them.

If you're not satisfied with your shot quality, you might want to consider if it's something other than your lens that is causing it; white balance, picture control setting, sharpness settings. The 18-105 is capable of taking remarkably good photos when presented with the right lighting conditions. But that can be said of most lenses these days.

 mosswings's gear list:mosswings's gear list
Olympus XZ-1 Olympus Stylus 1 Nikon D90 Nikon D7100 Nikon AF-S DX Nikkor 18-105mm f/3.5-5.6G ED VR +5 more
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