Re: Mach2 Unguided testing continues

Roland Christen

I haven't figured out yet how I could take advantage of this and still be able to dither frames.
You can dither all you want. That does not affect the custom rates that are calculated and applied to follow the actual sky motion above you.
Think of it this way: If you have Sidereal rate set, but it is slightly too fast and causes stars to streak in a time exposure, you could theoretically slow the rate down so that it matches the motion of the stars that you are imaging. Dither moves the next frame over a few pixels but does not change that tracking rate that you have set. The next exposure will still have round stars but they will be offset slightly from the previous one. That's how dither works - it has nothing to do with the tracking rate.


-----Original Message-----
From: Dean Jacobsen <deanjacobsen@...>
Sent: Thu, May 28, 2020 9:40 am
Subject: Re: [ap-gto] Mach2 Unguided testing continues

On Wed, May 27, 2020 at 01:15 PM, uncarollo2 <chris1011@...> wrote:
Below is a 15 minute UNGUIDED exposure I took last night with the Mach2 mount, purposely NOT polar aligned, off to the point where RA and Dec were drifting at 16 arc sec/hr and 88arcsec/hr respectively. I took a single 5 min drift measurement at the beginning of the exposure and used that to set the custom tracking rates for the axes (all done automatically in the keypad). It was good for the next hour of unguided imaging. A second and third drift measurement was added for 3 more hours, but clouds moved in.
With a good model the accuracy is better, in my opinion, than guiding with PHD2 or MaximDL. There is no jumping around, back and forth pushing and pulling of the axes according to momentary guide star positions and sky scintillation. It's a smooth motion, very accurate tracking under precise encoder control. This is with a 160EDF refractor of 1200mm focal length at .9 arc sec per pixel image scale.
The drift model resides in the mount controller, so actually doesn't need a laptop to store the data. The drift measurement can be done with a consumer digital camera, and then that camera can be used all night to gather images without ever having any guider attached.
Very impressive... amazing actually.  I am really looking forward to hearing more about this.  It is definitely something I could use.

I am among those who have cameras that require that I dither my frames.  I haven't figured out yet how I could take advantage of this and still be able to dither frames.
Dean Jacobsen 
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