Astrograph v Refractor

[BlueAstra]

I'm looking at getting an 80mm refractor to complement my C8, maybe a Meade 5000 or a Megrez 90, for wide field shots. However, I've come across astrographs like this one:

Maksutov Newtonian - Skywatcher Explorer 190MN DS-PRO Mak-Newt Astrograph

Are there any opinions regarding the relative merits of an astrograph verses the refractor? One thing that does spring to mind is the field of view. Would it be much greater than my current C8 + 1000D? On the other hand the astrograph operates at F/5 compared with F6 ish for the refractors, so grabs a bit more light. The astrograph advertises coma free flat field, so I wouldn't need a field flattener. Focus travel enough for my camera & OAG setup? So much to learn!

[Whippy]

It's a bit of an apples and oranges question really, especially as there's plenty of refractors that are astrographs! IMO, an astrograph is a scope of any design that's specifically designed for imaging rather than a 'normal' scope which is primarily designed for visual use.

The Mak-Newt has a focal length of 1 metre where as most 80mm 'fracs come in around the 500-600 mark so the Mak-Newts' FOV is a fair bit smaller than an 80mm 'frac. I'm guessing you're using a 6.3 reducer with your C8 so you're imaging at about the 1250mm mark right?

The shorter the focal length of the scope, the wider the field of view. Also guiding is easier with shorter focal lengths so on that respect the 80mm 'frac is a great idea. The Mak-Newt is a great scope though, no question. To be honest both of them completment each other very well. If you want wide fields it's the 'frac if you don't then perhaps the Mak-Newt is for you.

Tony..

[Tim]

Hi, I've been using an MN190 for a little while now, if you check my albums you'll see one dedicated to pics from it.

I like that it gets me in closer to the detail, it is very flat, and has an aperture bigger and faster than any 'frac I could afford. On the downside it needs collimating, but the MN190 holds collimation very well indeed, in fact, I havent had to redo it since last sept, and it has travelled from Kelling too.

Colour correction. I can see hardly any discernible shift in focus through the entire colour range, there is possibly a tiny discrepancy between focus for OIII emission and Ha, but it is very very slight, and if you were using a DSLR or OSC, you'd never see. As far as I understand it, most doublets will not be able to focus red and blue at the same point, so with a OSC camera like a DSLR there will always be a bit of a compromise as far as perfect focus for each colour is concerned. A good triplet should fix that, but cost that bit more.

As regards the OAG, you should be fine, but if you like, PM me to discuss fine details and measurements etc.

Cheers