Long Focal Length and fast imaging -does it exist?

[glend (Glen)]

Is there a way to get a 2000mm focal length in a f5 imaging scope? Sure a big newt would get there with a 400mm primary but would break my mount. Is there a light weight option, say 15kg max?

[Shiraz (Ray)]

probably the only way to get close to what you are looking for is with a sandwich mirror. As far as I can tell, the only mob that do anything remotely affordable seems to be http://www.ebay.com.au/itm/16-f-4-5-...-/201424023535. This one weighs 11kg and you may just get the associated structure built from CF with another 4kg. Better idea would be to get a stronger mount - then you can look at more conventional OTAs

[billdan (Bill)]

I wish their 14in F5 was at that price.
They only weigh 7Kg, I could build a scope around that and keep it under 15Kg.

Otherwise Glen your only other hope for 2000mm FL is an 8in F5 and the best 2x Barlow you can buy. It wont gather light like the 16in does though.

Regards
Bill

[gregbradley]

My CDK 17 with reducer is F4.45 and 2000mm. But it weighs 49kg plus imaging gear, plus plus and is expensive.

There are a number of astrographs appearing on the market. Ceravolo 12 inch has a corrector so it does F4.9. IDK have an F3.8 astrograph, so does Officina Stellare. Both very expensive scopes but probably pretty nice.

F5 is about the fastest you'd want to go for an easily managed scope. Faster than that requires an extra level of precision of flexure, camera squareness, focus etc.

Greg.

[glend (Glen)]

Thanks for the suggestions Gents. I do like the Ceravolo 300 but it is way beyond my budget and mount capacity. I agree about sticking to a f5 boundary if possible.

I don't think sticking a barlow on my newt is the answer because of the f implications, and possible flex issues.

[astroboof (Steve McN)]

Have to laugh with you grass hopper, not at you.

If you find this scope please share. I was going to suggest Dall-Kirkham but let it go.

Cheers,
Steve.