From: ScopeTrader.com (rharris_at_antispamdomain.not)
Date: Sun Nov 30 2003 - 18:10:55 EST
You are right! Terrestrial use isn't the best, but ya know one thing that's odd is that it has a GREAT macro on it. I can darn near get right up against a subject and still shoot!
Thanks.
--------------------------------------------------------------------------------
Richard HarrisScopeTrader.comnotify_.at._ScopeTrader.com
----- Original Message -----
From: Dale Ireland
To: digital_astro_.at._yahoogroups.com
Sent: Sunday, November 30, 2003 4:29 PM
Subject: RE: [digital_astro] Celestron 500mm mirror lens
Scopedude
The reason the f ratio is not stamped on it in big numbers is because
the true f ratio and the effective f ratio are not the same due to the
central obstruction. Not a huge problem for astro shots but a big
problem for terrestrial use. It makes sense that the dimensions indicate
a physical f ratio of f/6.5 but it probably shoots at, and is rated as,
f/8 speed, due to the light loss from the central obstruction. For
daytime shooting you have to shoot it in an "auto" mode. Aperture
priority obviously since it lacks a diaphragm. Only trial and error
manual exposures can determine the real effective f ratio.
Dale
-----Original Message-----
From: ScopeTrader.com [mailto:rharris_.at._elvis.com]
Sent: Sunday, November 30, 2003 12:32 PM
To: digital_astro_.at._yahoogroups.com
Subject: [digital_astro] Celestron 500mm mirror lens
Hey guys, I've asked this before a few months ago and I'm still trying
to find out the answer.
Has anyone ever seen one of these?
http://scopetrader.com/Messageboard/Files/Snap002.jpg
It's about 76mm wide, 500mm FL and gives pretty nice images.
I just can't figure out the F/ratio and was wondering if any of you had
ever seen one..
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