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06-01-2011, 12:45 PM   #16
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QuoteOriginally posted by jimr-pdx Quote
Thanks - I feel more on-thread with the Pentax eyepieces
Man, I thought that I had some serious astro-investments.. dual Ethi? Wow!
The 40mm Pentax XW with 46.5mm fieldstop has the widest FOV of any eyepiece that I know of and works great in my slow scopes like my 102mm F9 APO that gives it 22x , 4.5mm exit pupil and 2.9 deg TFOV.



06-01-2011, 01:33 PM   #17
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QuoteOriginally posted by jogiba Quote
Effective Aperture: f/12.5 with 80mm and Pentax PF-CA35 K-Mount DSLR Camera Adapter or about F6.3 without.

My Celestron 100mm ED spotting scope has a faster 540mm F5.4 or 1080mm F10.8 w/Pentax PF-CA35 K-Mount DSLR Camera Adapter :
Wow the difference is only 1/3 stop but both need a sunny day.

This compares with a Sigma 500mm lens and 2x TC.

Nothing else that is more lightstrong?
06-01-2011, 01:50 PM   #18
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QuoteOriginally posted by RonHendriks1966 Quote
Wow the difference is only 1/3 stop but both need a sunny day.

This compares with a Sigma 500mm lens and 2x TC.

Nothing else that is more lightstrong?
The 500mm Sigma zooms are F6.3 and F12.6 with 2x TC so they are about the the same as the Pentax PF80-ED .
600mm F5 :


Last edited by jogiba; 06-01-2011 at 02:12 PM.
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