This lens is very sharp wide open. I ran a test when I first got the lens.
I put Sirius in each of the four corners to look for problems. There were
none. It also is sharp with the teleconverter attached, but proper focus
is critical at that focal length! Any out-of-focus shows up really quick!
"Koebel, Alen"
<Alen.Koebel@christied To: "'astro-photo@seds.org'" <astro-photo@seds.org>
igital.com> cc:
Sent by: Subject: RE: [APML] OT: Big Pentax Lens for Sale
owner-astro-photo@seds
.org
10/08/2002 03:54 PM
Please respond to
astro-photo
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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