ZWOasi1600mc-c captures stars as doubles

fivel

Hello.

I have a very strange issue with this camera. It is connected to a powered USB 3.0 hub (Startech Industrial).

This issue occurs when using either oaCapture or Astroimager (both on a MAC).

The problem is, that almost every other sub capture has stars the are doubled. Each doubled star has the normal one and a much smaller one above it. I have attached an example capture for you to review.

Please advise me as to what could cause this issue.

Thank you.

Fivel

HH 3 Jan 2020_RGB_24_1x1_90s_ -31C_350_029.jpg

riklaunim

Looks like the frame is moved, like if your mount wasn't tracking accurately and for like short part of the exposure the mount quickly changed position causing double-alike effect on bigger stars.

fivel

Thank you riklaunin for your reply.

Yes it looks like that, but why does it do that on nearly every other sub?

That is what confuses me. With 90 second subs, it is to short to be a PEC issue.

This only started happening a couple of weeks ago. And as I mentioned, it happens with two different capture apps.

Could there be a possible problem with the USB communications to the camera?

Fivel

chuckwagon

That is a tracking issue and not the camera. What mount are you using? Are you guiding the mount? 90 seconds is more than enough time for a Periodic Error issue to show. However, this type of image is common when guiding and encountering a backlash issue. So knowing the mount and whether you are guiding will help.

fivel

Hi chuckwagon, thank you for your info.

My mount is a Mountain Instruments MI-250.

I was not guiding, The stars (not including the double issue) were pretty round, so it tracked well.

I will need to test different exposure lengths, to see if the issue gets worse or better.

I will also recheck the balance, and the worm to spur gear tightness, for either backlash or it being to tight.

Since it just started happening recently, I will try to think of any changes I made, besides installing the new powered USB hub.

Fivel

chuckwagon

I've read that the MI-250 can be difficult to balance, and does not like perfect balance but performs better with a little bias to keep the gears engaged and avoid "bouncing." Since you aren't guiding, and the backlash issues that can cause are not an issue, it is possible there's an issue with gear mesh or balance, so definitely check those. If it's a recent change, how's the weather been? If it's colder, that can have an effect, maybe the lubrication is getting a little stiff or "sticky" and needs to be checked. It's also possible some contaminant has gotten into the gears and is making them jump a bit. You may not be guiding, but you could use PHD2 to profile the mount's motions and see if the jump occurs regularly. Or just watch a live feed of a star for a few minutes and see if you can detect it.

fivel

Thank you again Chuckwagon. Your suggestions are very thoughtful and I will check them out.

When i balance the RA, I always use an East offset. I will try a mess offset with the DEC as well.

I will then finish with new PEC trainings.

When all this has been (hopefully) addressed and fixed, I will be testing the camera for other issues, such as possible amp glow.

But that is for another time.

Fivel