Scope vs Scope (What to choose)

[pike]

OK, so i know apeture is king, but what about foal length.
I am looking at two scopes, SkyWatcher reflectors, both 150mm ap, but one has a focal length of 1200mm and the other 750mm.
The 750mm is more expensive so I am guessing that is the better choice.

I will be using it for deep sky viewing mainly, some plantary stuff and eventually strapping my DSLR to it.

So which would you choose and why?

Next question, I also have the chance to go for an Orbinar 200/800. I have not heard that brand before so dont know if the bigger appature is wirth the no-name risk. Any thoughts?

[rustigsmed (Russell)]

the longer focal length creates a tighter field of view so you are more 'zoomed' in with the longer focal length. you don't see many f/8 newts these days. if it were me i'd probably go with the f5 newt - in fact that was my first scope.

I don't know anything about the orbinar brand but the scope is f4 which means you will definitely need a coma corrector for viewing.

what are you looking to put it on top of?

[Astropic]

+1 for F/5 Newt scope.

I did a quick price search for the 150mm F/5 Newt scope
- Ozscope $749.95 (aluminium tripod) Link
- Ozscope $899.95 (steel tripod) Link
- Bintel $729.00 (aluminium tripod) Link
- Andrews $599.00 (aluminium tripod) Link
- Optics Central $599.95 (aluminium tripod) Link

I will stay away from unknown brand like Orbinar. Better off stay with Synta products Skywatcher/Saxon/Orion and Celestron

[kens (Ken)]

Another +1 for the F/5 for DSOs where you want a wider field. Same as my scope.
For planetary you can add a barlow which are generally easier to get hold of than focal reducers.
Make sure whatever you get that it is designed so you can focus your DSLR at prime focus.

[ZeroID (Brent)]

F8 will make a longer scope of course but it will also be more tolerant of focus and eyepieces. From an amateurs viewpoint it would also be easier to grind and make. A lot of smaller mirrors 4", 4.5" are made at f8, I think because it makes the scope look bigger in the shop ..

F5 seems to be the norm these days as much as easier for storage and transport as anything. F5 is also easy to make nowadays with modern factory processes. Less critical for alignment and mechanically easier for building truss type scopes, less chance of deflection.

F4 will be very critical on alignment and focussing and tough on cheaper eyepieces. Only really for experts IMHO.

[Eden (Brett)]

Not sure what your budget is, but if you take the time to shop around, you can certainly save a lot of money.

I picked up a brand new 200mm F4 Newtonian (Skywatcher Quattro... scope only, no mount or tripod) for $575 last year, which included shipping from Gerry Gibbs Camera House Perth to Melbourne...and it was/is being advertised for as much as $1300 elsewhere.

[doug mc]

The f/8 is more likely to have a better figure on the mirror. Shorter f ratios require more work and have a bigger chance of having more spherical aberation. You should be able to get a low enough power to get a 7mm exit pupil in the f/8 scope. But it photography is your thing than the shorter scope would be best. The shorter scope would tax the mount less also.