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Old September 29th 05, 06:29 AM
Brion K. Lienhart
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Randall Ainsworth wrote:

In article . com,
Siddhartha Jain wrote:


Given two lenses, one a prime (say 28mm) and the other a zoom (say
28-75mm) and both with an aperture of f2.8 -
- Will the prime be brighter than the zoom because it has fewer lens
elements?
- Will the prime be sharper wide open than the zoom at 28mm?

Ofcourse, a lot will depend on the particular makes and models being
compared but is there a rule of thumb?



F/2.8 lets the same amount of light through regardless of the lens
design. F/2.8 is f/2.8.


Nope. F:2.8 is solely based on the size of the lens. Obsidian is glass,
you can grind it into a lens shape, but if you use it as an element in a
lens, you're going to get some reallllllly slow shutter speeds. Of
course that's an extreme case, the difference between plain old glass
glass, and exotic flouro-silicates is only a few fractions of a percent.