Fast focal ratio newt? is it possible?

[Insane Climber (Jason)]

Hello
I have been practicing photography for about a year and a half now and i feel that im ready to go for a more serious scope. I intend to use the SW neq6 which will limit me to about 20kg. What i realy want in a scope is large appature and fast focal ratio for wide field imaging. However i am haveing some trouble decideing which way i should go. Obviously a celestron edge with the farstar mod would be fantastic but the price is very offputting. this leaves me with either trying to make a schmidt camera or takeing the Newt approach.

Is it possible to use a focal reducer with a newt and still get a flat field? I understand that the reducer will greatly increase the effects of coma but what i don't understand is how the coma corrector works or if it is adjustable. obviously a mod like this would require shortening of the newt tube and replacement of the secondary with a larger unit. So i would like to be as sure as i can that it will work befor i start. Any input or discussion would be greatly apprechiated.

Jas

[mch62 (Mark)]

You could look at an ASA focal reducer corrector. They have a 0.73 reduction and correct for coma. So an F4 becomes about an F3. http://www.astrosysteme.at/eng/correctors.html
Very expensive but are used in there fast Astrographs.
I wouldn't worry about there Astrographs unless you want to morgage your house but for around $2200 you can make a very good quality 10" f3.5 to f4 Astrograph yourself using readily available products and add the Korrector or there are a few Commercial F4 Newtonians floating about you could add the corrector to but the corrector would be worth more than the Commercial Newtonians. Check out my old Astrograph -sale pending
http://www.iceinspace.com.au/forum/s...ad.php?t=58061


Mark

[Ken]

You can use a meade 6.3 reducer on a f4.5 Newt and get pin point stars across a aps size sensor the only down side is a hot spot in the center of the image. I did this a couple of years ago with my 18 " with good results but sold the reducer and bought a w.o. .8 reducer which is useless on the Newt. but brilliant on my ed80. Last week I was having the same thoughts as yourself and came to the conclusion that the Keller type of reducer was the best but out of my price range at the moment so I ordered a Antares 6.3 reducer from OPT on Monday, it maybe a bit more flexible in its positioning than the meade. I am also fitting a larger secondary mirror in the scope plus the use of flat field shots in the image processing should give super fast f2.8 images with no coma.
clear skies Ken.

[Satchmo]

Originally Posted by Insane Climber

this leaves me with either trying to make a schmidt camera or takeing the Newt approach. :

You can't go past the Baader MPCC to coma correct Newts from F3.5 to F5.

Astrotech make a new one trhat will be good for both visual and photography.

http://www.astronomics.com/main/prod...roduct_id/ATCC

Mark

[mch62 (Mark)]

Mark would this unit be a better proposition for my upcoming Dob or would the Paracorr with it's tunable top for my TV eyepieces still be the best?
Mark

[Satchmo]

Definately go with the tunable top Paracor for visual. Non tunable coma correctors are always a compromise visually.

Mark

[Insane Climber (Jason)]

Thanks for the input there guys, its good to at least hear that im not way off track with this idea. I especially like the idea of useing a lower reducer of .7. I was origionally thinking of just useing a .5 but machining the 2" nose cone shorter to lower the amount of reduction. I have been looking around for a suitable newt, and so far i realy like the astrotech imaging newt which has baffels and a longer front section. Its only 8" though. The 10" skywatcher is also high on my list because its so cheap. Someone has one for sale on the forum now for only $450. I was thinking it would be possible to move the secondary down insted of shortening the tube to give a longer front section. Does any one know of an easy way to make baffels?

Thanks again for the input
Jas

[mldee (Mike)]

Originally Posted by Insane Climber

Thanks for the input there guys, its good to at least hear that im not way off track with this idea. I especially like the idea of useing a lower reducer of .7. I was origionally thinking of just useing a .5 but machining the 2" nose cone shorter to lower the amount of reduction. I have been looking around for a suitable newt, and so far i realy like the astrotech imaging newt which has baffels and a longer front section. Its only 8" though. The 10" skywatcher is also high on my list because its so cheap. Someone has one for sale on the forum now for only $450. I was thinking it would be possible to move the secondary down insted of shortening the tube to give a longer front section. Does any one know of an easy way to make baffels?

Thanks again for the input
Jas

MY WO 80 triplet looks like it uses multiple stick on 1/2" foam tape rings. I'd also read somewhere on a forum that they work, just make sure the glue sticks well.