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Hi Fragchmp & All,
I agree with most of those who contributed above -- I'd go for the 12.
I had a chance nearly 5 years ago to do a test report for a magazine on the 12" GSO dob and found the optics to be excellent. All round construction of the 'scope was very good considering the price. Fortunately I own an excellent 'scope to compare it with -- my own 31cm f/5.3 on a GEM which has a mirror by Mark Suchting.
I evaluated the optics using my own eyepieces (they were Televue plossls and Naglers) of known quality and also the GSO supplied ones. The star test on the GSO I evaluated was excellent. I detected none of the common faults frequently found in mass-produced optics. There was no detectable astigmatisim, it seemed to be well parabolised, there were no apparent zones or turned edges on the mirror. A Ronchi eyepiece was applied at focus and it similarly showed no detectable defects -- the lines were ruler straight (as they should be in an _eyepiece_ ronchi), evenly spaced and evenly illuminated.
Mars was at its BIG opposition (2003) and it showed excellent detail -- hardly less than my Suchting mirror. In summary, in the 'scope I tested, the optics appeared to be of very good if not excellent quality.
I have since looked through several other 10 and 12" GSOs and they too seemed to have pretty good mirrors. There have been some others who have had (and expressed) unsatisfactory views but they seem to be in a very small minority.
My only complaint with the optics was a "design" issue not quality. The secondary mirror in the ''scope I tested was a 70mm minor axis job which I felt for a visual 'scope is unnecessarily large -- it is almost "photographic" in size. The secondary in my own 'scope (which has a slightly longer fl at f/5.3 as opposed to f/5) is only 54mm. The GSO could easily get away with something about 10% smaller -- say 62mm. This would pull the secondary obstruction by diameter down below 20% -- a desirable thing to obtain best contrast.
But, all in all, the optics were difficult to fault and the overall execution of the telescope was good -- it presents as excellent value for money.
As said above by many, 12" -v- 8" is a big increase in light-gathering power and it will make a substantial difference on deep-sky stuff. Nebulae will be much brighter and more detailed. Globular clusters will regularly exhibit a well-resolved appearance, and to the experienced observer who knows exactly what to look for, some spiral galaxies will start to show evidence of spiral arms.
The view of the planets will be much brighter and colours more saturated. However, 19/20 nights, the level of detail visible in say Mars or Jupiter will be the same in both 'scopes. On that 20th night, the 12" will show a better view.
Whichever way you go, best of luck with your purchase.
Best,
Les D
Contributing Editor
AS&T
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