Why do older camera lenses have faster F-stops?

Started Apr 14, 2013 | Discussions thread
Contributing MemberPosts: 614
Re: Why do older camera lenses have faster F-stops?
In reply to MiLei, Apr 17, 2013

There is a another reason why older lenses were often faster.  Digital focal planes have micro lenses on each pixel to increase their light collection.  For this work the ray bundle has to be symmetric on an axis perpendicular to the focal plane.  This is called telecentric from the rear.

Otherwise there will be serious light fall off away from the center.

This makes design and construction of really fast, faster than f/2, lenses very expensive.

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