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Old 08-05-2021, 03:51 PM
kosborn (Kevin)
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kosborn is offline
Join Date: Mar 2018
Location: Canberra
Posts: 397
Originally Posted by Emuhead View Post
So a 10" mirror on an eq6r (f4 or f5) is not too heavy after all, I'm hearing more & more from people who have done it successfully. Just might consider that.. 1000mm f4 or 1200mm f5 is the question, guess this thread has shown it makes no difference to detail/resolution as long as the pixel scale still falls in the sweet spot, it'll be the exact same image if cropped to match, so may go the f4 route for the speed & to keep the windsail size down.

I've done everything I can to save weight on the Newtonian including carbon fibre tube and OAG. Wind is still the killer though. If you go f/4 keep in mind what you'll use as a coma corrector. I think Andy had a Sidereal 1000mm f/4 with a Paracorr which actually has a 15% Barlow effect. I think that means he was actually imaging at 1150mm and f/4.6, not much different to my 1270mm and f/5. I use a Baader MPCC III which can be used at f/5 and above and leaves the focal length and f ratio unaltered. I don't know if there are coma corrector options for Newtonians faster than f/5 that leave the focal length unchanged... I think in general an f/5 Newtonian is cheaper than an equivalent f/4 (and the Baader is cheaper than the Paracorr). Obviously a 1000mm Newt has less length than a 1270mm Newt when it comes to windsail but I don't know how much difference that extra 270mm actually makes in real life.


Last edited by kosborn; 08-05-2021 at 05:01 PM.
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