Thanks to you all for your advice which I will take on board. I have some further questions to ask; if I use my dslr ( I have both a Canon 5D mk iii and a 1DX) coupled to one of my big lenses, probably a 300 mm f2.8, how would you attach this to the EQ head and how would you mount a spotting scope or guide scope to the setup. Also I have read about the effects of dark current, especially on the 1DX. Am I better just going for a astro camera in the first place?
The other thing is would you mind clarifying the point about large filters. Are these the ones that fit behind the lens over the D