The rest of the message is:

At the risk of showing how ignorant I may be.....

I was reading and came across a specification of the LX200 F/10 10". It
stated that the focal length was 2500mm and the aperture was 254mm. Does
this not calculate to F/9.84 not F/10?. Does every one just round? If so
how did they come up with F/6.3, what is that focal length? Since it is a
SCT is that just the average (the focal length does change when the primary
mirror moves?) I had heard that the Focal length is 100 inches. Can anyone
confirm this 2500mm focal length and my method of calculating the F/??.

Thanks,
Rick in Tucson



-----Original Message-----
Sent: Saturday, August 25, 2001 6:12 PM
Subject: [M]: Re: Curious question on F-Stop...


> Date: Sat, 25 Aug 2001 12:44:48 -0700
> Subject: [M]: Curious Question on F-Stop (not sure if this is the
name) but F/10, F6.3 etc.

We lost the rest of your question, but yes, f-ratio means the same thing
on telescopes as on camera lenses. It is the focal length divided by
the aperture. The difference is, with telescopes it isn't adjustable.
But if you put a camera body of the prime focus of the telescope, it is
indeed working at f/6.3, f/10, or whatever, and the exposures of daytime
objects will be the same as with a lens at that f-ratio.

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