From: [email protected] [mailto:[email protected]] On Behalf Of Chip Louie
Sent: Friday, February 7, 2020 1:51 PM
To: [email protected]
Subject: Re: [Losmandy_users_io] Computer for remote operation

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Hi Derek,

The ASI290MM-mini will likely only be used as an autoguider. The question I have been considering is should I spend $150 more for the 290's higher QE rear illuminated, smaller photosites to pick up some additional sensitivity and improved centroid precision, by my calculations maybe 20-30% better which would leave some headroom for the small pixel camera I have. I have been hemming and hawing over this decision for almost two years but back then was considering the QHY178 with its 2.4um rear illuminated sensor but a $450 price and a distinct lack of any real need had me put it on a back burner until now. With the current requirement to use an ASI autoguider to move to the ASIAIR-PRO the need for a decision is here now and the ASI290MM-mini looks right at this time for my needs.?

I'm using a Stellarvue 50mm f/4 guidescope with a QHY5L-II mono threaded into the helical focuser, it is?in a SV one-piece clamshell with a Losmandy D/V adapter used to clamp the guidescope to the top dovetail of whatever imaging scope I use. This is a bomber rig, zero flexure and no chance for misalignment once it is setup. So yes, completely different from your maximum overkill SV80mm f/7 scope.?Unlike your conservative known to work large guidescope solution I looked for the highest possible efficiency and lowest possible weight solution that I could be confident would work. I used a math based model and determined there was no need for a large 80mm guidescope, my assumption was that the then new CMOS autoguider cameras with their higher QEs than previous generation autoguiders could be used with smaller guidescopes. I just played with the numbers and figured out that I should be safe with a 200mm f/4 guidescope and 70%+ QE 3.74um pixel autoguider camera even under the worst case scenario and still get sub arcsecond resolution. To my delight it worked great and even with the M10" f/6.3 SCT the old 2-piece worm block G11's guided PE was well under 0.5" RMS.?

The only reason I am considering the ASI290MM-mini is for the potential improvement for autoguiding. If I want to do planetary imaging would use one of the ASI183MM or MC Pro cameras and set the ROI to 1280x720 to get 100+ FPS for planetary work. With the bespoke Parallax/AT130 f/6 apo loaded up with a 2" 2X PowerMate I get an f/12 instrument @ 0.32"/pixel with a 0.11x 0.06 degree FOV which if you use a sample rate of 3x Dawes is close to ideal for a 130mm optic. I may get slightly tighter images by using the M10" f/6.3 SCT with 2" 2X PowerMate for an f/12.6 instrument @ 0.15"/pixel with a 0.05x 0.03 degree FOV which if using the same 3x Dawes sample rate is just about perfect for the 254mm optic. Either scope should give solid results with the M10" f/6.3 SCT probably really limited by seeing.?

The QHY5L-II-mono autoguider has the same sensor geometry and specs as the ASI120MM mini so they are pretty much interchangeable as far as autoguiding performance and flexibility goes.?

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Chip Louie - Chief Daydreamer Imagination Hardware