RE: [APML] OT: Big Pentax Lens for Sale

["Koebel, Alen" <Alen.Koebel@christiedigital.com>]

Does this lens produce acceptable images wide open at f/2.8? 
I've heard of several brands that need to be stopped down 
to f/4 for good results. For such a lens, I have to wonder 
if a 300mm f/4 (or more commonly f/4.5) lens operated wide
open might not work about the same as a stopped-down f/2.8
lens. Less weight and less cost. Of course, it depends on 
the specific brands and models being compared, but as I 
understand it the general rule of stopping down one or two
f stops doesn't necessarily apply to telephotos that are 
already at these kinds of focal ratios (because they're 
easier to design). Maybe the lens experts here can weigh in
on this.

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