Sorry if this has been asked before, but I don't remember when.
I have a AD-10 f/1250, f/5 Dob that I use for wider views of the sky. I also have a Meade LS-8 f/2000mm f2000mm f/10 computerized scope for when I can't find stuff with the Dob....lol
I plan on using them both together sometime when a friend comes over to join me, plus help me lift them with my 70 yr. old back. So I was wondering what an object would look like side by side.
So, I'll pick M13 for this example. I put in a 20mm eyepiece in the SCT for 100x and a 13mm in the Dob for 96x. Will I see a noticeable difference at the eyepiece with only 2" of aperture?
Same question on a planet, say Jupiter? Maybe nothing on the moon as it's so bright to start with.
Before you can compare them you need to be comparing apples with apples, to do that you must make a number of assumptions.
1) Both scopes are of equal optical quality. (ie lets assume diffraction limited, which is reasonable).
2) Both scopes are properly collimated
3) Both scopes are properly cooled.
Given the above 3 prevailing conditions there isn't anything the 8" SCT will do optically better than the 10" dob.
The laws of physics see to it that this is so. Each optical surface introduces aberrations and light loss, albeit small in each case. The SCT has a lot more reflective and refractive surfaces than a newtonian
SCT = Corrector Plate, Primary Mirror, Secondary mirror, Star Diagonal. 4 surfaces
Newtonian = Primary Mirror and Secondary mirror only = 2 surfaces
The 8" SCT will also have a much larger secondary than the 10" Newtonian (about 35% compared to 25% in the 10% dob). The larger secondary causes additional diffraction and affects the MTF curves. This only applies to visual not imaging. A premium 10" Newtonian will have a further smaller secondary than a 10" mass produced dob. Usually a premium 10"/ ~F5 Newtonian will use a 1.83" secondary for an 18% CO whereas the 10"/F5 Asian made dobs use about a 63mm secondary.
The 10" dob will give much better wide field low power views. You can still wind the power up with a 10" dob by using shorter focal length eyepieces but you can't widen the FOV and reduce the power in a SCT beyond a certain point due to the long focal length and slow F-ratio.
While I have only ever owned newtonians and a couple of refractors over 47 years as a visual observer, I have spent a lot of time looking through colleagues SCT's at every type of target available. Given equal aperture I am yet to come across any SCT that can come remotely close to the views through a decent well set up and tuned newtonian. Giving 2" of aperture away is like taking a knife to a gun fight. The SCT will have a greater "depth of focus" but at F5 the depth of focus is reasonable on the Newtonian. The SCT will have a far greater tendency to "dew up" than the Newtonian. Corrector plates are renowned dew magnets.