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imaging at long focal lengths with the EQ6 takes a fair bit of tenacity.. I have taken a few images at 1750mm (11" @ F/6.3) and one or two at 2800mm F/10. but it took some serious serious patience, only ever 2nd or 3rd sub was usable, I dont know if that was due to periodic error or wind wobbling the scope etc... Thats not to say that it can not be done... with smaller scopes that catch less wind and weigh less, it may be easier..
Guiding with a 1900mm focal length would be a right pain in the bum, as finding guide stars may not be the easiest task... The chip on guide cameras is alot smaller than most imaging cameras, I know that with my DBK31 + ST80, the field of view is nearly equal to my QHY8 + C11 @ F/6.3.. Its a fairly narrow field, especially when you need to land a mag 6~7 star in there for guiding... on the otherhand, if you were able to find a suitable guide star, I'd say the image would come out spot on.
For starters, short focal length is THE way to go... At first, I figured, 'yeah, everyone says short FL is the way to go for starters, but I'll figure it out with the long FL, then going to short will be easy..' I had nothing but frustration trying to start imaging at 1750mm.. I got an ST80 and guided my Megrez 102, first night with it all running properly, I produced images that I was very very proud of.. and have done a few times since..
Id say, ST80 + ED80 to start out, once you've got the whole setup under control, and imaging nicely.. then start thinking about narrow fields, consider whats the best narrow field scope for imaging (a 150mm F/12.6 is perhaps not a great imaging system, as its very slow and will require LONG exposures) Something like a 2nd hand C8 or 8" Meade, giving 2000mm @ F10, and the option of using the 6.3 reducer with 1260mm focal length, which will be double that of your ED80, giving you two very different perspectives for imaging, it wouldnt be to heavy, and with the ST80 as a guid scope, would be a great little setup for narrow fields...
All in time is the key... Get used to imaging the easiest way possible, as your confidence in your gear and skills grows, then consider the next step..
Alex.
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