RE: [APML] Optics Question

["Thomas W. Earle" <twade@bmi.net>]

Oops, I made an error in my calculation, is the equivalent speed 1/3
stop faster, not 1 1/3 stop faster?

Wade 

-----Original Message-----
From: astro-photo-bounces@seds.org
[mailto:astro-photo-bounces@seds.org] On Behalf Of Thomas W. Earle
Sent: Friday, January 07, 2005 10:01 PM
To: astro-photo@seds.org
Subject: [APML] Optics Question

I have a Pentax 67 300 mm F/4.0 EDIF which has a lens diameter of
approximately 74 mm. I also have a Takahashi FSQ-106N.  Obviously,
if you just look at the speed of the two lenses (i.e. F/4.0 and
f/5.0, respectively), the 300 mm should be about 2/3 of a stop
faster; however, the FSQ-106N gathers 2x the amount of light given
its larger lens diameter.  Does this mean its equivalent speed
compared to the 300 mm is really 1 1/3 stop faster?

Thanks in advance,

Wade


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