Which scope should I buy?

[Astrokev]

Hi All

I'm looking for advice on buying a new scope. My current scope is a 10" f6.3 Newtonian (OTA is homemade, using commercially bought optics), which I've had for years. This has served me well over the years, but I'm now keen to upgrade to something of better quality more suited for imaging.

My interests are deep sky and lunar and planetary imaging.

I know there's probably not a single scope that is best suited for both these targets, so I may be looking for 2 scopes.

My guess is I'd be looking for a shorter FL frac' for deep sky, and a longer FL scope (SCT ?) for planetary. The difficult bit is knowing which models to go for - any suggestions? I have an NEQ6 mount so am only looking for an OTA(s)

For a frac' I'd like good quality glass, and as much aperture as I can afford.

For a long FL scope, I'm tempted by Celestron SCT  9.25 or 11", but I also see and hear good things about the Skywatcher MN. Any others I should consider?

Hope this request isn't too vague. Thanks for any suggestions.

Kev

[michael.h.f.wilkinson]

For lunar and planetary imaging, aperture is king. The MN 190 is a good deal small, and although it has a very good rep as a visual and DSO imaging scope, and would probably do a very decent job on planets with the right PowerMate or Barlow, I think the C9.25 and C11 would be better. The C9.25 has a very good reputation as a planetary scope. This may be due to its slightly slower primary, which makes control of spherical aberration easier. Some say the C9.25 is very close to the C11 in planetary imaging performance, but that may in part be due to the seeing. A C11 needs better than average seeing to outperform a C9.25. I personally am looking at the C11 as a successor to the C8 I have had for many years now

[pete_l]

49 minutes ago, Astrokev said:

My interests are deep sky and lunar and planetary imaging.

I know there's probably not a single scope that is best suited for both these targets, so I may be looking for 2 scopes.

My guess is I'd be looking for a shorter FL frac' for deep sky, and a longer FL scope (SCT ?) for planetary.

As you point out, what you need to resolve the conflict between DSO imaging and planetary imaging is a range of focal lengths. I would suggest that the simplest way to do that is with a single OTA and some accesories: focal reducers and powermates.

 

As far as FRs go, there is a selection that offer a reduction to 80%. And a Meade FR/FF that will take an F/10 SCT down to a respectably fast F 6.3. The thing to watch out for is that the imaging circle these produce will still illuminate all of your CCD. There's no point reducing your focal ratio if the resulting image is too small to fill your sensor.

In the opposite direction, it is easy to get up to F 20 or 30: focal lengths measured in metres!

As you will have guessed, I would therefore suggest you look at an F10 SCT as a good starting point and then consider what range of focal lengths you want and choose an aperture that will combine nicely with the right acceessories to deliver that.

[ollypenrice]

In principle you should bring it down to a shortlist of two and then buy both...

lly

[Astrokev]

But which two!  

[Freddie]

I have a 925 and a MN190 and would never use the "wrong" one for wrong target, they just don't work!!  I find them very good at what they are designed for though and am very happy with both.

[Astrokev]

Hi Freddie. Thanks.

In your opinion, where does each scope excel ?

thanks. kev

[ollypenrice]

I'm not a planetary imager so can't comment on that other than to suggest you look at Damian Peach's website and his comments on the C9.25/C11 etc. 

For me a deep sky imaging APO refractor's qualities are not primarily determined by aperture. For broadband imaging you will certainly need good colour correction (less important for NB imaging) and, depending on your chip size, a big enough flat field. You'll also want a focuser which works without slipping or sagging or otherwise wasting your precious clear sky time! The faster they are the harder they are to make and the bigger they are the harder they are to make fast.

With about £2000 to spend I went for a second hand Takahashi FSQ106N, the old fluorite model. This is a 106mm F5 instrument built like a tank and unlikely to depreciate in value now. It has an enormous natural flat field so there is no flattener to chip distance to worry about. If I had the same choice to make again today it would be the same one without hesitation.

Buying new I'd be looking at the Esprits. It doesn't really matter about the aperture for imaging. The important changes between models concern the focal length. Deep sky objects range from very large to very small so 'yer takes yer pick.' A six inch refractor isn't better than a three inch, it's just different. It takes a different picture.

Olly

[gorann]

I think you should also look into a Celestron EdgeHD 8" since your mount can handle it better than the larger SCTs. The flat field of that one makes it useful also for deep sky AP, including galaxies. It is of course also quite good for planets. Then you also get two scopes in one if you get the focal reducer (takes it down from f/10 to f/7, so FL=2000 mm and 1400 mm). The focal reducer for the Edge 8 is also much cheaper than the one for Edge 11 (they do not make one for the Edge 9.25).

For refractors Olly gave some good advice. You may even think about going for a 3" - 4" one. I have two Explore Scientific apos and I am quite pleased with both, and they cost much less than something like a Tak. The newer ones in their line are probably even better than mine as they use the equivalent of a FPL-53 glass and you can get them with Feather touch focusers . Teleskop Express also have some that looks very interesting:

http://www.teleskop-express.de/shop/index.php/cat/c224_Flatfield-APO-Refractor-Teleskope.html

Cheers

Göran