ST80 piggybacking ST120 - 13" dovetail required?

[emadmoussa]

Hola,

I have my SW ST80 piggybacked on top SW 200p on EQ5. I'm expecting to get a SW ST120 to use for grab-and-go observing and, perhaps, astrophotography (It's weird there's a spelling red line under this word - it's an astronomy forum...duh!). Anyway, do I need another 13" dovetail to get things working. Or the medium one already with the ST120 will do the job?

Second question, how good are the results with this combination: Canon EOS 50D + ST120 (chromatic aberration aside) + EQ5 mount?

Third question, Gosh...even me think I'm such a big mouth...pla pla pla. Some will say that the EQ5 is not the best out there for DSO astophotography. But I also heard of 'rumours' on ways to improve its performance?!