Re: Mach2 - Elongated stars

Ray Gralak

Hi Yanzhe,

Can you zip and post your PHD2 logs, as well as APCC/AP V2 ASCOM driver logs?

There might be something useful there.


-----Original Message-----
From: [] On Behalf Of yanzhe liu
Sent: Sunday, March 7, 2021 10:12 AM
Subject: Re: [ap-gto] Mach2 - Elongated stars


I will check my mount serial number later as I just packed everything due to rain forecast.

My camera's orientation was 0/180 degree, so I assume top to bottom elongation would be DEC.

I dont have any picture of my setup, I just tore it down since it will be rainy this week. My setup is
FSQ106+OAG+16803, image scale is 3.5".
I was imaging Rosetta Nebula, after it was just past meridian for 2-3 hours.

I used PHD2 drift for PA, it reported <5' PA error, I am waiting for polemaster adapter so I can confirm I get good PA
next time.

DEC was out of balance because my setup was rear end heavy, if it was in balance position then I could not rotate
my CCD in all directions. My guess is that the DEC balance was off by less than 1lb. In the next test, I can balance
DEC to see if the issue still exists.

My suspicion is that if DEC balance is off, then DEC might creep under gravity, even PA is perfect. So you might
see DEC continually drift then gets corrected by PHD2 periodically.


On Sun, Mar 7, 2021 at 9:35 AM Roland Christen via <chris1011@...> wrote:

Couple of questions:

1 - what's the mount's serial number
2 - which axis is the elongation
3 - which direction was the scope pointing (RA-Dec)
4 - what scope and focal length or what is the arc sec per pixel.
5 - do you have a picture of your setup?

One comment about balance - it should be easy for you to completely balance the scope with the clutches
loose. Can you estimate how many lb out of balance your scope is in Dec? Normally i would not think this would
have any effect, but doesn't hurt to check this.

Roland Christen
Astro-Physics Inc.

-----Original Message-----
From: yanzhe liu <liuyanzhe@...>
Sent: Sun, Mar 7, 2021 12:44 am
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
- DEC balance was slightly off, camera heavy. Is Mach2 DEC sensitive to this? Will the guiding/image be

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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