[PeteMo (Pete)]

There is a defininte difference between a 10" and 12" but how much difference depends on what type of object you are looking at. I've a 10" SkyWatcher dob and had the opportunity to have a look through it's bigger brother. The 12" seemed a bit brighter to me with Omega Centauri, along with galaxies like M104 (sombrero), M65, M66 and M96. A lot of differences will be subtle, like extra detail in cloud bands on Jupiter/Saturn, or extra definition to whisps of gas in nebulae etc. The 12" dob user didn't complain about light loss when he viewed through my 10" scope, so for most run of the mill stuff you may not notice much difference.

Although a 12" dob mirror has 1.44 times more surface area than the 10", please remember that this does not equal 1.44 times brighter, or sharper.
If I remember correctly, to double the amount of light you see you will need a mirror with 4 times the area, (square law). Going from 10" to 12" won't be like going from a 60W bulb to a 100W bulb. More like a 60W to 75W, for want of a light bulb anaolgy. I certainly don't regret getting my 10".

In the latest ads for BinTel in AS&T, they state that the 8, 10 and 12 dobs have "8 x 50 90 degree Finder Scope", so the spec is identical to Andrews minus the 6mm and 25mm Plossls.

It's amazing just how much dobs have come down in price, even SkyWatcher 12" dobs are now under a grand, whereas they were close to $1400 when I got my 10" SkyWatcher last year.

Enjoy!