jpoulette Posted February 2 Author Share Posted February 2 (edited) 36 minutes ago, Lee_P said: Specific advice here for @jpoulette -- one of the things that makes the Askar FRA400 a neat little 'scope is that there are no backfocus requirements; so long as the image is in focus, the backfocus is automatically correct. However, if you use the reducer then be aware that you will need to get your backfocus just right (probably 55mm or thereabouts) otherwise you'll get streaky corner stars. I'm not saying don't use the reducer, but it's just something to be aware of. Speaking personally, I never used a reducer with my Askar FRA400. Regarding "fast" optics in general, I try to sidestep the whole issue by treating astrophotography as a marathon rather than a sprint. My previous 'scope (the FRA400) was f5.6, and my current 'scope (Askar 130PHQ) is even slower, at f7.7. But *shrugs* it's fine, I just keep plugging away until I collect enough data. Granted, I might change my mind on this topic if I ever use a speed demon like a RASA 😁 Good advise - thanks. I picked up the reducer mainly because it was available - it seems to be 'out of stock' for quite a while. I need to acquire some data first and then evaluate (see the results with my own eyes), and adjust if necessary. The reducer may work perfectly at some point, given that the object is properly placed in the center of the image. I've had a little experience with the classic Petzval design - I'm hoping that the inherent sharpness of the center area of the exposure will help, given the objects I'll be looking at. I'm not quite sure what the function of the 5th element in the FRA400 is - but a few images should enlighten me on that. 😀 I have a good 180 degree view centered due north from home - so there are several objects that I've had my eye on for imaging. I'm hoping Stellarium images like this one will give me a decent representation of the stock lens - detector relationship. Edited February 2 by jpoulette 1 Link to comment Share on other sites More sharing options...
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