Star adventurer - problems with unguided dithering

[AnonymousAnimosity]

A few nights ago I tried doing unguided dithering of the skywatcher star adventurer through EKOS. The tracker is connected via the ST4 port to a guide camera (which I've yet to use) that is controlled by EKOS. I left the pulse duration at the default value (0.5s), which should be enough to dither for enough pixels at 6.55"/pixel (samyang 135 and canon 100D).  Stacking was done in SiriL. 

I shot about 120x120" lights, calibrated with 15 flats and biases and this is what the background looks like:

there are still visible patterns but it's a bit better compared to what I usually get.

The following night I took about 100x180" lights, calibrated with flats and biases:

Yesterday I further increased the dither pulse duration in EKOS (0.8s if I'm not mistaken), this time double the amount of subs:

 

I am not sure what I should do differently to solve this problem. Any ideas?

 

Edited August 14, 2021 by AnonymousAnimosity

[alacant]

Hi

Assuming you have the guide camera connected (via whatever-your- guidecamera is called) in the guide module and dither pulses are indeed being received by the mount...

To lose the walking noise, you need to move the camera in declination as well.

To optimise RA at 135mm, set the maximum dither in EKOS  (currently 10) and delay the start of each frame in capture by say 10s to allow the rig to settle. Whilst you're in capture, set something reasonable for the guiding settle distance. 1.5 px works ok for us.

Stack using a clipping algorithm. sigma 5, 2 or windsored 3,3 work well with our 700d, but YMMV.

Cheers and HTH

 

Edited August 13, 2021 by alacant

[michael8554]

The image scale is 6.55"/pixel 

To dither the 100D by the commonly used 12 pixels, the mount needs to move 12 x 6.55 = 78.6 arcsecs.

So does a pulse of 0.5ms, or 10, achieve that ?

Michael

 

[AnonymousAnimosity]

23 hours ago, alacant said:

Hi

Assuming you have the guide camera connected (via whatever-your- guidecamera is called) in the guide module and dither pulses are indeed being received by the mount...

To lose the walking noise, you need to move the camera in declination as well.

To optimise RA at 135mm, set the maximum dither in EKOS  (currently 10) and delay the start of each frame in capture by say 10s to allow the rig to settle. Whilst you're in capture, set something reasonable for the guiding settle distance. 1.5 px works ok for us.

Stack using a clipping algorithm. sigma 5, 2 or windsored 3,3 work well with our 700d, but YMMV.

Cheers and HTH

 

Thank you, since there is only one parameter to be set for ungided dithering in EKOS I will get back to this and try the settings you suggest when I find the time to sort out guiding.

7 hours ago, michael8554 said:

The image scale is 6.55"/pixel 

To dither the 100D by the commonly used 12 pixels, the mount needs to move 12 x 6.55 = 78.6 arcsecs.

So does a pulse of 0.5ms, or 10, achieve that ?

Michael

 

My bad, I mean to write 0.5s! Although I must have read somewhere that a few pixels were enough I will definitely increase the pulse duration and aim for 12 for the next attempt. Thank you for pointing out the mistake.

Edited August 14, 2021 by AnonymousAnimosity