Choosing between Nikon D5200 or Sony NEX6

Started Aug 27, 2013 | Discussions thread
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120 to 35 Senior Member • Posts: 1,248
Re: The zooms are not dark hyenadog!

Caerolle wrote:

I wonder how many people know that f is focal length divided by aperture diameter?

It is not strictly necessary to know this for photography (as opposed to the relationship between aperture, shutter speed and ISO).

But for judging lens sizes it is helpful to know. In this case, 85 / 42.5 = 2.  For a 1.8/50 lens the maximum diaphragm diameter is 27.7 mm. The diaphragm assembly includes the blades around the opening and depending on the design cam add up to the same amount. Total lens diameter is thus around 50 mm. For a 2/85 lens the maximum diaphragm is 42.5 mm. A compact legacy Nikon 2/85 AI-s is 64 mm in diameter but it does not include electronic diaphragm, auto-focus and OSS motors inside the lens. As a very rough guide, add 55% to the dimensions of the SAL 1.8/50 to get the approximate size of a SAL 2/85.

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