Re: Mach2 - Elongated stars

Roland Christen

Take a short exposure (1 sec or less) of a bright star inside, outside and at focus. I was shooting the other day when the temperature was dropping rapidly after sunset and got heat plumes for about 1 hour in my 160 refractor. Made the stars look oval during that time. I could easily see the heat plumes when the star was defocused. Things like this should be checked when you start off in your imaging run. After about 2 hours the stars were perfectly round during my focus runs.


-----Original Message-----
From: Ray Gralak <iogroups@...>
Sent: Sun, Mar 7, 2021 10:24 am
Subject: Re: [ap-gto] Mach2 - Elongated stars

> One issue bothering me is that I got slightly elongated stars across the entire image (15min Ha sub).

Can you describe your imaging setup? (Telescope, camera, image scale, etc.)

Is it possible the issue is optical (collimation) or caused by vibrations from the camera's fan?


> -----Original Message-----
> From: [] On Behalf Of yanzhe liu
> Sent: Saturday, March 6, 2021 10:44 PM
> To:
> Subject: [ap-gto] Mach2 - Elongated stars
> Testing new mach2 for a couple of nights. It works great out of the box and I am very pleased.
> One issue bothering me is that I got slightly elongated stars across the entire image (15min Ha sub).
> The exact same telescope/CCD were used with another mount and stars were round, I am wondering what I should
> check (I think there was due to some setup issue, but I could not figure it out).
> - Used OAG for guiding, so there should not be any flexure.
> - CCD orientation was 0/180 degree. The stars were elongated top to bottom.
> -  I did polar alignment with PHD2 drift align. PA error should be < 5'. The field rotation of each sub is ~0.01 degree,
> much larger than the other system (but elongated stars do not look like field rotation, they were same across the
> image)
> - Both RA and DEC guiding curves looked smooth, had similar RMS. DEC correction was mainly to one direction.
> - DEC balance was slightly off, camera heavy. Is Mach2 DEC sensitive to this? Will the guiding/image be affected?
> I dont think any of the above is of particular concern, except DEC balance. Any comment/help is appreciated.

Roland Christen

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