What would you buy from these choices of OTA?

[pyrasanth]

I'm planning a new observatory which will be based around a small dome.

I plan to use my Paramount MX+ as the mount in the new observatory. My love of astronomy is in the deep sky so I will be keeping the RASA for wide field work but I need a longer focal length instrument for increased image scale. The optics on the Celestron Edge HD 11" are a bit too soft for my liking & I don't think the image circle will fully illuminate a large CCD chip being I think only 42mm diameter.

I'm considering 2 instruments unless you have other suggestions the AG optics 14.5 or the Planewave CDK 14. The Orion optics AG 16 might also be a contender but I can't find any reviews to confirm the quality of the optics which makes me nervous.

I know I probably wont be able to utilise the full resolution of such an instrument from my none dark sky site but at least the optics would come into there own on those rare nights of good seeing.

I don't know at this stage which is the best OTA. I think it might come down to personal opinion but the AG appears to have really good specifications but the question remains- is it in the same league as the Planewave.

Let me know your thoughts.

Happy New Year.

[Peter Drew]

I've no direct experience of the telescopes you list but I would expect the optics in the AG16 to be at least equal to other high end telescopes of this design and aperture. Have a look at their gallery to see if images with their AG16 are what you hope for. 

[ChrisLX200]

Those are fairly large aperture instruments and having a large aperture like this offers 2 things: impressive light capture and high (potential) resolution. You still need a fast focal ratio to avoid needing long exposures all the time - so preferably you're looking for f/6 or better. The resolution may be a problem in that you may not be able to reap the benefits without the sky conditions to support it. It's not much use having optics capable of resolving 0.5" if your 'seeing' is 2" at best. In addition, the large aperture instrument needs more time to acclimatise to conditions and is perhaps more prone to suffering loss of resolution on nights of poor seeing. For that reason I would bias the purchase towards optical excellence rather than the largest aperture that is within budget. From experience using my NP127is over the past couple of years I know that this 5" OTA will resolve right down to the limits of my seeing, I can record such fine detail that it is going to be very tough to beat it with ANY insturment from my obseving position. This gave me pause for thought when selecting a larger aperture OTA myself to provide a larger image scale for those smaller targets - what am I actually going to gain going with a larger aperture?

You see, if I take my image of (for e.g.,) M106 and crop/scale it up there is (apparently) as much detail visible within it as in some published images taken with much larger aperture instruments, so I really do wonder whether by buying a 12" aperture ODK I will be able to significanlty improve on this. I guess I will find out over the coming season, and it's true that the extra light-gathering capability must count for something - provided I'm not imaging at f/8 or slower (which would negate most of the benefits I think).

As to choice of manufacturer well, as I mentioned, aim for optical excellence - at the cost of 2-6" of aperture if necessary. I'd rather have an excellent 10" scope than a 16" with anything less.

ChrisH