In a message dated 3/14/01 4:26:37 PM Pacific Standard Time,
mickeytr@xxxxxxxxxxxxxxx writes:
<< Roger- You have me very confused. How is a f5.6 anything slower than f8?
What do you mean about the f4.5 mirror that is about a f7.5? Are you saying
that mirror lenses have overly optimistic ratings? Or is there something
else that I missed earlier in the thread?
-Mickey
>>
Hi Mickey-actually me-John Raymond, who has stated that a mirror lens and
it's f stop does not equate to a "normal-non-mirror lens" f stop.
Maybe someone here on the list can explain it to us both. Bending light and
the loss of light caused by this bending would be part of a lens's f stop's
rating I would think.
I recently took my (non mirror)Tamron SP400mm f4 out and metered it next to
my Vivitar 450mm f4.5 Series 1 mirror lens.
The mirror lens was about 3 stops+ slower than the Tamron "regular" lens. I
have read that there was a discrepancy about mirrors before but was suprised
at the difference. And, accordingly, the viewfinder was much dimmer with the
f4.5 mirror than the super bright f4 on my Tamron 400/f4.
I would have to assume that any mirror f8 lens out there is more like f11.
Looking forward to hearing other's thoughts.
John Raymond
Olympia, WA
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|