Dither problem.

Cameras, telescopes, focusers and other hardware
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brujo
Posts: 13
Joined: 24 Jan 2019, 20:41

Dither problem.

Post by brujo » 27 Jan 2021, 01:12

I guide with AstroArt, but have a problem with dither.
Every image that was dithered is capturing while moving the mount.
Here is an example. Maximum shift on x and y is 2 pixels.

Iver
Posts: 41
Joined: 08 Jan 2019, 04:32

Re: Dither problem.

Post by Iver » 27 Jan 2021, 03:57

Are you imaging with an SCT, could it be mirror shift?
Iver

brujo
Posts: 13
Joined: 24 Jan 2019, 20:41

Re: Dither problem.

Post by brujo » 27 Jan 2021, 06:05

Yes, I am using a Celestron 11, but It can't be mirror shift.
I am dithering every 3-rd image , and every 3rd image shows this "double" star.
It looks like dithering is going on while taking images.

fabdev
Posts: 274
Joined: 03 Dec 2018, 21:43

Re: Dither problem.

Post by fabdev » 27 Jan 2021, 16:18

During the dithering, the cross in the autoguide window becomes blue, so it's possible to verify visually when dithering starts and ends.

It's strange that "double stars" are almost equal, it looks like a 25 seconds / 35 seconds exposure.

Maybe the bigger pulses sent during dithering caused something in the mirror or in the mount? You could solve setting Spiral Dithering, which moves the reference by only one pixel at a time. Or just use 1x1 dithering which will give 5x5 different positions on the image (dithering 2x2 moved the image by 10 pixels).

Iver
Posts: 41
Joined: 08 Jan 2019, 04:32

Re: Dither problem.

Post by Iver » 27 Jan 2021, 17:36

Are you guiding through a Guide scope? It could be mirror shift and or differential flexure. If you are using a guide scope try not dithering.
Iver

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