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Hi Natalie,

Conventional wisdom says I'm wrong. But I think the focal length of the 50mm finder is likely fine, depending on your autoguider camera you may just need smaller pixels. A few years ago I tested using my then stock configuration G11 with HP worms, straight 2-piece worm block drivetrain (Bellevue discs to preload the bearings) with PHD2 running a QHY5L-II mono cam screwed to the helical focuser drawtube of my SV50mm f/4 guide scope in the SV clamshell clamped to a Vixen dovetail on top of a Meade 10" f/6.3 SCT (weighs as much as my C11!). The results proved that a G11 with a Gemini I, even in the oldest possible configuration when carefully setup and adjusted in the COLD can track with a very good PE of 0.48"-0.34" RMS when piggybacked with a solidly mounted guide scope setup. I then retested that same night within minutes and repeated the test with the QHY5L-II mono at prime focus and did not see any difference in PE error RMS. I did the same testing a year later using the same mount and same HP worms after it was updated with the new tucked-in servo motors and Gen II OPWs - interestingly, maybe not surprisingly the overall PE error and shape of the curves was the same. The autoguiding testing was done in a dark sky location in the eastern Sierra, about Bottle 1+ which on a good night you almost cast a shadow from starlight here.?
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This tells me that a short but tall 30+ pound imaging load with a piggybacked but solidly mounted 50mm f/4 guide scope and autoguider camera with 3.74um pixels is more than good enough for imaging with an 10"-11" SCT. I can assure you that it is much easier to find a good guide star with a 50mm f/4 scope than a 3,000mm+ focal length scope and a pick off prism. I'm not going to say you should not use an OAG to autoguide an SCT but it is not because using a small piggy backed autoguider system is inadequate which obviously if well configured they are not if the testing is any indication. But if you can find a way lock the SCT's mirror and use an external focuser with autofocus going piggybacked for the autoguider is something you might consider to save time.?

Me, I'm waiting for some parts to arrive. I plan to do some driveway imaging this year with my G11G now with spring loaded OPGs and the same Meade 10" f/6.3 native SCT operating at f/2.5 with an ASI183MM PRO and filter wheel. I will be using the same SV50 f/4 guide scope up top but an upgraded tiny pixel ASI290MM mini autoguider camera. But I was also expecting the L.A. Kings to do better than they did two season ago, instead they burst into flames. Derek knows what I'm talking about. ??

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Chip Louie - Chief Daydreamer Imagination Hardware