What do I need to start astrophotography?

Firstly, get the book Making Every Photon Count.

To track the stars, and compensate for the motion of the Earth, you need an equatorial mount, and the best you can afford. The rule of thumb is that any given telescope needs a mount twice as robust for imaging as it does for visual observing, and you should be entirely ready to spend more on the mount than on the telescope tube itself.

When doing prime focus astrophotography - the norm for taking pictures of deep-sky objects - the telescope is acting as a camera lens. As such, you can equally well use the camera lenses you have and take some nice images. With a shorter focal length and lighter weight, it will be less hassle than trying to use a big scope straight away. Long term, you can certainly mount the 8" tube you have on an equatorial mount.

1) Go join your local Astronomy club .. there will be lots of existing astro-photographers who will give you practical help ..

2) You need an adapter (which replaces the camera lens) to link the camera and telescope focuser tube.

HOWEVER

a) Unless your telescope is motor driven (so can track the stars) you can only image bright objects - in this case, the Moon, constellations & bright groups of stars like the Pleiades ... Nebula & Galaxies will be much too dim for the short (ie seconds at most) exposures you can get without 'star trailing' on a non-tracking mount

b) Dobsonians are not really intended for imaging - you may discover that your focussing tube assembly won't 'wind in' far enough to allow the camera to focus .. if yours is one such, you either need a special 'short focus' camera adapter, a new focussing assembly, or, if all else fails, move the primary mirror ..

This is far too complicated to explain in a few paragraphs. I'd recommend reading the chapters on astrophotography in the latest edition of The Backyard Astronomer's Guide by Terence Dickinson and Alan Dyer (Firefly).

for an individual with a color camera and a tiny 8" telescope it would be a total waste of time , you need black and white CCDs to capture stars and planets no color CCD is sensitive enough and you need an accurate equatorial mount that can be mounted in a totally vibration free location , even a car or truck driving by can wreck an attempted photo