Quote:
Originally Posted by bluesilver
Just was looking for something would deliver more sharper / detailed views i guess you could say.
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Peter, thing is you already have a scope that delivers what you want!
Why are you saying that your dob isn't up to the job?
The planets are a low contrast affair. With a 12" dob, your issue could just be too much light, which will overwhelm the subtle planetary detail. But the detail is all there, be it a 12" Newt like yours or a 12" SCT. The larger aperture will also provide greater resolution capability than a 7" or 8" Cassegrain of whatever design.
Have you tried using filter with your dob? Polarizing filters or Neutral Density filters will help tone down the brilliance without altering the colour. Colour filters will help bring out different planetary features too.
I have seen the same level of planetary detail in my 8" f/4 dobbie as an 8" SCT. But a larger aperture out does both of these for planetary detail.
Also, do not expect to see planetary detail in the same way as in photos. Photographs are all very processed to bring out improved contrast and colour saturation that is not the same as with looking through an eyepiece. Remember how I mentioned above that planetary detail is a low contrast thing? The photographic process of stacking and post processing helps to overcome this, but it an construct, not a true representation of how things appear through the eyepiece.
f/ratio is also not a problem. f/ratio is only a photographic parameter. An f/15 cassegrain will give the same image brilliance as an f/5 Newt, AT THE SAME MAGNIFICATION. So again, it's not your scope that is a problem. And both an f/15 cassegrain and f/5 Newt will both have the same amount of "difficulty" of showing planetary detail at the same magnification. It's then how you use the scope in order to help bring out the detail.
By way of example, I have owned two Maks, one a 7" the other a 9". Both Russian made beauties. I actually do find it easier to see detail on the planets in the 7" than the 9" and ONLY because those two extra inched of aperture makes the image that much brighter. However, the detail in the 9" is there, I just need to use this scope a little differently. Filters help a lot. Steady seeing is a must (which brings up another possible solution for you below*), filters also help, but patience is the key.
While aperture is King with astro scopes, the achilles heel of large aperture is seeing conditions. Larger apertures are much more sensitive to poor seeing than smaller apertures. This I've noticed between the 9" Mak vs the 7". This means that being able to use high magnification with a larger aperture can be more problematic than a smaller one. On those nights of poor seeing, I don't bring out the 9" Mak, or the 17.5" dob, but I do use an 80mm refractor or an 8" dobbie, respectively, and stick to lower magnifications as the image will be less affected by heat haze and the session is still a productive one. Most nights you just can't use anything over 150X, and that's that
Adapting your planned viewing session to suit conditions is your Plan B.
A friend shared with me this gem that all of us should have as our mantra:
" Plan for 50X per inch, expect 25X per inch most nights, and pack a barlow in case you hit the jackpot!" 
* One trick that may you may like to try before anything else is to stop down your 12" dob. Make a mask that goes over the opening of your dob, with a hole in it that is say 8" in diameter. You will then have yourself an 8" f/ 7.5" Newt. You will of course notice that the image will be dimmer (smaller aperture, duh...), but it may help improve the amount of planetary detail you do see - by virtue of that dimmer image! This stopping down of the aperture will also help a little more if seeing conditions are not ideal for a larger aperture. *
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There are all manner of tricks that are available to us in order to get the best performance out of our scopes both for our eyes and cameras. It's then just a matter of knowing these and remembering them... sometimes easier said than done...
This is why I think your post is a great one, as it makes me recall what all the tricks in the box are and then dust some of them off again as sometimes I too forget them! So, great thread, Peter!
