I would save some $$ and woukd not get the small 72ED. Its a FPL51 fast doublet and not very suitable for imaging (unless you use a minus violet filter), and overkill for guiding.
Instead I would spend the saved $$ to get a better triplet and would rather choose the SW esprit 120 which is a FPL53 triplet, optimized for imaging. But of course, it is much more expensive than the ES127.
Using an OAG would give the best guiding results, however you could also start guiging using the finder as a guide scope.
Then upgrade to the OAG, depending on your learning curve. Even starting using the OAG is fine, the only difficulty is focusing the guide cam, but you do it only once.
The QHY5L-II (same sensor as the ASI) is fine for guiding using a finder. It just requires a Ircut filter, which is now included onto the windo glass which protects the sensor.
Carbon fiber is not a good idea for imaging refractor : the optics focal length changes together with the temperature : it shriks when the temperature decreases. An aluminium tube alo shrinks when the temperature decreases, so it can compensate more or less the optics focal length changes. This is not the case of carbon tubes.
So if you grab the ES127, take the aluminium version, it is good enough and even better than the carbon version.
Also star test it carefully when you receive it. The main concern with these far east refractors is the quality control. Some are excellent (especially the "golden samples" they issue first) while some other....
Then do a short exposure (i.e. no need to guide) of a star field and observe the stars at the center : they should be round. Not always the case...
You will need a field flattener at one point (grab one optimized for this focal length). When you have it, observe the stars at the corners. If the sensor to corrector distance is well tuned, the stars at the corner should be round and sharp.
A second hand "old" AP 130EDF (I mean the first version, the F6 ) is still an excellent astrograph and fine grab and go telescope while beeing cheaper than the GT version.
Edited by olivdeso, 20 December 2014 - 11:44 PM.