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Skywatcher 72ED (Refractor), Stella Mira FF, EFW, EAF, ASi183MM Pro, ASiAir Mini Hi All. I’ve got two problems with my second setup: 1) Stars are not right even when in-focus 2) When running and AF routine, I get terrible graphs with points all over the place. Could the two be related? And does anyone have any suggestions on where to start looking in terms of problem solving? TIA!   |
8.11
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I can't help you with auto-focusing because I don't use it. The image you posted looks like a small part of your frame, maybe from a corner? Seeing the full frame would be helpful. Maybe manually focused to help sort things out?
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The image is zoomed in so the stars can be easily seen but this is from the centre of the frame and as in-focus as I can get
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You have a significant amount of tilt, might be in the objective glass but I can't really be sure. Remove the FF and test again at the center of frame. No auto-focuser. I downgraded the same scope to guider as it wasn't worth for much else…
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I’ll have a strip down of this at the weekend hopefully. The 72ED was a good starter scope and I’d like to swap it for an Askar FRA400 but that’s not possible just yet. Do you think the star shape could be causing the AF star size issues?
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A high degree of tilt makes focusing difficult, in a way similar to what defocusing does but probably not as extreme. I am no expert in how auto-focusing work as I don't use it but my guess is that it would be fair to assume this to be at least a contributing factor. As said before, the best way to assess this to remove everything but camera and scope and test again.
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Just wondered how consistently bad it is and just as bad every night? The variability in the auto focus run also happens with bad seeing which if you are unlucky can happen over a run of nights. I expect that Andrea is right about tilt but motion blur is another way that the all the stars can be distorted in the same direction - so worth checking what the mount is doing too ?
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I'm seeing this on most nights. Although the seeing hasn't;t been great recently, my other scope is focusing perfectly every time, even when pointed at roughy the same area of the sky. According to ASTAP, there is also no tilt in the system  |
7.29
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Looks to me like a combination of bad optics plus bad seeing. A question regarding your af routine. In Nina, you can specify the the number of measurements for each focus step. Can you increase this value in your routine? That can greatly help reducing scatter in your af plot, especially with bad seeing, wind or similar things. It will not fix your star shape though. |
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8.11
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You do know that it's not a requirement to use auto-focus to get things in focus right. In your post you state that the stars are not right, even when in focus. You should be able to set up a 1 or 2 sec. exposure loops and manually focus. Zoom in to some medium bright stars ear the center of the frame and make then as small as you can. You can also monitor your FHWM or HFR and tweak it to get the number as small as possible. With a little practice you should be able to get into the critical focus zone. We know you don't have tilt so if your stars still look like comets then you'll know, it's a problem with the optics.
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Just to update this. I managed to get the focus problem sorted but the star shape was still pretty bad. I've ordered a ZWO FF65 to replace this scope so I'm sure it will be a nice step up from the 72ED.
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1.81
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Craig Dixon: I have same scope and flattener. I had vaguely similar issues with apsc dslr, but after getting a much smaller imx533 I noticed tightening the lock/whatever screw underneath seemed to cause/exaggerate the issue. Seems fine now |
