Image shifting when using SGP?

General
#1

Setup:
TV 102
QHY 268 C
Losmandy G11T with Gemini 2, most recent firmware
ZWO 60 mm Guide scope and ZWO 290 camera for guiding

Hi There!
I am new to SGP and have been playing around with it now for a few sessions. Still sorting out quite a bit, but I have noticed one thing and I thought I would post it here to see what folks think. Basically I have noted that when I run my scope, camera and Guiding through SGP, I see pretty significant drift in my images when stacking over the course of a couple hours. However, with the same setup where I use sharp cap to do image capture and guide directly with PHD2, I see virtually no drift.

By Drift I mean that images captured through SGP shift over time, so that there are significant stacking artifacts at the edges of the image. My exposure time is 180 Seconds per sub. Interestingly, the stars are more or less round. it is just that they have shifted position from frame to frame.

Thanks!

JMD

#2

How long are your exposures? I’d try doing a longish (10+ minutes) exposure and see if you have elongated stars. If so, then your guiding is off.

If not, then the next question would be whether there is consistent drift from frame to frame, or whether it just happens after some other event (focusing, meridian flip etc)

#3

Thanks for the response. The drift it consistent from frame to Frame. Seems to be only happening when I am using SGP to capture and follow PHD2. Does not seem to happen when I capture using Sharpcap and PHD2 directly to guide. I have switch between the two approaches a couple times and it seems consistent. I am betting I have something set wrong in SGP(probably more than one thing:-). Still wrestling a bit with it quite a bit. Crawling up the learning curve. It is definitely interesting process to learn.

Regards,

JMD

#4

So then you need to determine if it is happening within frames or between frames. Again, if you take a long enough exposure it should answer that question pretty easily.

If it’s happening within the frame then you would need to look at your guiding params, mount tracking speed, potential differential flexure or mirror shift (if they apply to your setup) etc

If it’s happening between frames then you should check what SGP and/or PHD2 are doing between captures. e.g. is guiding disabled during frame download?

Either way, you’ll need to provide more info on your setup - logs for both SGP and PHD2 would also help.

#5

Thanks Steve! I will do as you suggest.
Regards,

JMD

#6

Do you have dithering turned on in SGP?

#7

Sounds like you have (Dither) enabled. With dither the frame shifts a few pixels between frames.