as mentioned in a previous post, i am looking to move up in aperture and as i am yet to look through a 12", is the jump worth the money for not only viewing at the eyepiece (main reason) but aswell as astrophotography?
Try some astrophotography with the 8" before uping your aperture. If you really do have the astro-bug, and you want to up it to a 12" (this is pretty big), you'll need an EQ-6. Around 2Grand or more for both (not Go-To).
The 12" is best, if you can afford it, and can lift it/move it, and can fit it in your car for travel.
FOr astrophotography, start with you 8" as above. Depends also what type of astrophotography you want to do and what you plan to use as your imaging camera.
I have a 10" sct but for astrophotography use an 8" SCT usually with an f6.3 focal reducer. If you want to do astrophotography an 8" will give an easier learning curve, better photos and less hassle than the 12". Learn on the 8" and then if you still want to go the 12" but most people never exhaust the capabilities of a well collimated and guided 8" SCT.
Optically there is no comparison. The 12" eats the 8" but its bigger, heavier, has a larger storage footprint and is harder to transport.
For AP the 8" would be great to learn on. It would allow you to perfect your alignment, learn the capture software/hardware and image processing. If you really get into it then a heavier mount for the 8" would be easier on both the pocket and back.
Simple arithmetic (forget pi), the radii, 4 squared is 16, 6 squared is 36; over twice the light collecting area. If you can manage the 12 inch that would better.
The main difference is the 12" will show heaps more galaxies and everything will be about one magnitude brighter, but the 12" is too big and too heavy to move around easily.
So does my 10".
