Visual observing: big APO (130mm) refractor VS. big (12") Dobson.
If you live under a nice dark sky or don’t mind driving to one and want to do visual observing of deep sky objects, consider getting the Dobsonian.
If you live in an urban location with mild or heavy light pollution, consider getting the refractor. For deep sky observing use a tracking mount and add an inexpensive astro-video camera ($300) and do some EAA (Electronically Assisted Astronomy). You will see more detail in a few seconds from a light-polluted backyard with the refractor/video camera combination than you will with the larger Dobsonian under a dark sky used visually – albeit on a screen, but the views are really something to see. And you can use your scope in mild to heavy light pollution without traveling – a huge bonus. The more expensive but powerful image intensifier used with a 5” apo is an eye-opening, deep sky observing experience. Again, you can use an intensifier in mild to heavy light pollution but they are costly.
Adding modern light gathering technology to the refactor negates the Dobsonian’s (used visually) light gathering advantage and need to travel to dark sky locations.
For the 12” Dobsonian to use it full resolving potential on the planets you will need: excellent seeing, which is (or can be) rare in most locations, aggressive thermal management, perfect collimation, excellent optics (Zambuto) and tracking at high power is nice (maybe a platform).
If the above is done and the seeing is very good/excellent and the planets are high in the sky the larger scope (with a good mirror) will definitely deliver the goods.
If the above sounds like too much for your location’s seeing or your observing style, consider the refractor. A 5” apo will not disappoint on the moon and planets. They: acclimate reasonably quickly, have excellent thermal stability, excellent contrast and light scatter control, do not need collimation, are more conducive to shorter sessions for a quick looks at the moon, etc. and are a little less fussy with the seeing conditions in most backyards.
This is what Sky and Telescope had to say about the SV 130mm refractor when they reviewed that scope…
“A 5-inch refractor is ideal for high resolution visual use on the sun, moon, and planets. Its resolving power of 0.9 arcseconds is perfect for sampling the typical seeing of 2 to 3 arcseconds common at most amateur observing locations….”
“…and they (5-inch refractors) aren’t as susceptible to poor seeing as large scopes.”
If planetary imaging is in your future, consider the Dobsonian but with some type of tracking. The refractor will also do nicely but for planetary imaging aperture is better, as one can eliminate poor seeing and add contrast etc. in processing.
If long exposure, deep sky imaging is in your future, consider the refractor.
If Ha solar observing or imaging of solar prominences and disk features is in your future, consider the refractor.
I’m not going to copout and say get both, I don’t think that’s what you want to hear. I’ll just say that NO scope is the best at all things. So, if you want “specifically” what the Dob does best, then get it.
But with the “right accessories” (video camera, GEM, solar filter, etc.)”, the versatility of a high quality, 5” apo refractor comes pretty close to being a perfect, single scope solution that can grow with you as your observing interests expand.