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Maximum useable Field of View

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#1 Guest_**DONOTDELETE**_*

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Posted 09 October 2003 - 03:05 PM

I'm interesting for maximum useable Field of View according to following state:
"A common mistake is to buy one or more expensive long focal length highly corrected 2" wide field eyepieces, and then attempt to use them in a two inch diagonal behind an f/6.3 reducer/corrector, thinking they'll get a wide enough field to see BEHIND them... But all they really see is the secondary mirror shadow obscuring their field of view and then get mad at the focal reducer."

- With other word what is the maximum Field of View with acceptable field vignetting for Meade 7" Mak and it's different for 1 1/4" or 2" diagonal - ocular and with or without focal reducer.

- What combination give maximum Field of view

- It's something different with binoviewer

PS: I don't need explanation of formula Field of View = eyepiece field of view/magnification. I'm asking these on many places, but without good answer. I need it to know what to buy.


#2 Guest_**DONOTDELETE**_*

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Posted 09 October 2003 - 07:42 PM

Oldi,

There was a discussion a few days ago about larger eyepieces with larger FOV. I don't know if you read it or not, but it was an excellent discussion.

55mm Televue Plossl Thread

Tom

#3 Guest_**DONOTDELETE**_*

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Posted 10 October 2003 - 01:46 AM

Where (in which threade)
I can't found it

#4 Guest_**DONOTDELETE**_*

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Posted 10 October 2003 - 01:49 AM

Sorry I miss link on your answer

#5 Guest_**DONOTDELETE**_*

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Posted 01 November 2003 - 12:09 PM

A friend has a 10" LX-200 f-10 system, 2540mm f.l., with a 2" Tele Vue diagonal and adapter (called a "Rich Field Kit"). The Meade/Celestron 2" SCT diagonals only have a 1.5" opening in the front, and they may strongly vignette the field of view. She has an excellent University Optics Konig 40mm Mk 70 with a 70* apparent field for 63.5 power and a 1.1 degree true field. With a f-6.3 reducer, that drops to 40 power and increases to a 1.75* true field. This combination DOES NOT show a shadow from the secondary. It does vignette at the edges, though, as the field stop is not a sharp, crisp black. Also, you can't point it at the zenith as the reducer/diagonal combo is too long and it will hit the bottom of the fork (Tele Vue now makes a "shorty" 2" diagonal and adapter to correct this). As your 7" Mak is just a little longer in focal length than the 10", I'd think that it would work reasonably well. But it is hard to say without knowing how large the image circle produced by the scope is. I think that you will vignette the edges of the field of view, but I doubt that you will have a shadow from the secondary visible. With this combination, your apparent field may be less than 70 degrees due to vignetting, but whatever it is, it will be the widest field of view possible.
Warpd



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