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dothead
super member
Reged: 08/13/08
Posts: 163
Loc: Heidelberg, Germany
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Re: FET-300/EM-3700
08/14/08 07:28 PM
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Daniel,
Interesting you mention Pons' scope. Maybe a Petzval type refractor would be the way to go to avoid thermal problems caused by too much glass (too many elements) in one place.
By the way, Daniel, have you ever heard of the 10 inch Petzval (2 front, 3 rear elements) APO made by the Colorado based EQUINOX INTERSCIENCE company (you can google their website). Looks like a truly professional scope (for instance, it sports an 8 inch focuser!); with a $90000 price tag for the OTA alone, it's certainly out of reach for all but the most affluent amateurs (talk about a dream scope!).
My dream refractor would be a 20 inch F/30 folded D&G achromat. To mount this thing, a AP El Capitan mount would surely be way too small! But Markus Ludes of APM Telescopes sells an equatorial mount which weighs 1000 lbs without counterweights (for Euro 24000) which should handle the OTA.
Together with a Zeiss 160 mm eyepiece (70 degres AFOV, 180 mm field stop, 8 inch barrel), which Markus also had on offer for quite some time (sold now), you could attain a TFOV of 41 arc minutes, despite the 600 inch focal length of the 20 inch - F/30 D&G. The color correction of this scope should be roughly equivalent to an 6 inch F/9 achromat (devide the f-ratio by the aperture (in this case, 30/20 or 9/6 and get 1,5. The old rule is that once you get over 5, achromats reach apochromatic colour correction. For instance, an 3 inch F/15 achromat (yes, the old Tascos! (Royal company objective lens) show almost no residual colour even at a magnification of 50x per inch)).
Cheers,
Ralph
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