Dithering....

So, I believe I've reached my limits. I can't make dithering to work. I always get this back:




SkyGuider Pro, DSRL & Lens, ASI224MC as guide. Properly balanced, properly powered, great cable management.

I've tried different settings, with guide box, with dither px, algorithms etc. and I just can't make it to work.

PS. Two axis option is disabled.


Any idea is more than welcome!

I'd be happy to look if you posted a log (enable debug logging for guiding), and also your guidelog (parallel directory to the logs directory).

But before you do, here's a few questions:
1) Does it guide well without dithering? This is showing quite large guiding error. See if you can get it to guide under 2 pixels rms (really ideally under 1 or lower). I'd like to see good guiding before attempting dithering.
2) Why 1-axis? Why not guide in DEC?
3) Can you run PHD2, and in particular their guide analyze or whatever it's called and see if that comes up with some warning? [There is no such analysis tool for KStars at this point.]
4) Of course, as always, the most important question is, how are your captures?

Good luck!
Hy

Hello!

Certainly, I'll search to activate the debug logs.

1. After a lot of tries and settings changes, I've pressed reset to default (guide-->option tab) and after a while, RMS went to 1-1.5.
2. SkyGuiderPro, so only RA
3. I've read about it and I have to try it.
4. My captures are great (for my taste), but I am trying to combat the walking noise, that's why I need it.

The thing is that I have also Stellarmate OS and with exactly the same settings dithering is working fine even with the max 10px. So I'm trying to understand why is it different.

Do you have a guiding deviation set in the capture module?

No, at least not in purpose. I'll check it.

But if it is ON, the captures should stop, correct? My captures are working properly.

Yes you are correct, just trying to think of anything else it could possibly be. Weird that it is happening regardless of your settings.

I noticed that SEP can have issues with color camera images. I'd try to use 2x2 binning and see if that improves things...

Dithering will try to move in a random direction, I'm wondering that if your Dec axis is fixed, whether dithering is going to help you, I think it will just give you oblong stars, as the dither can only move in a single axis.

gilesco wrote: Dithering will try to move in a random direction, I'm wondering that if your Dec axis is fixed, whether dithering is going to help you, I think it will just give you oblong stars, as the dither can only move in a single axis.

No, why would it create oblong stars? It's not moving during the exposure....
But what usually happens is that RA-only dithering will not be able to remove the 'rain', the stripy appearance coming from fixed pattern noise of the camera. At least you'd need a stronger dithering (larger max), and much more images.

Well, because dithering normally moves one or two pixels across a 2D plane, but in your case it will move 1 or 2 pixels up and down a line, because that is all it can do.
I'm just not sure that it would be effective for you. I imagine it is failing because it is not taking into account your 1-axis guiding and still trying to dither both RA & DEC.

Let me add more Infos into this.

This is the stack with STF from the internal guider with the above settings and 10px. (1 day before this thread)


After creating this thread I've tried with the PHD2. This is the result with 4px into Ekos and 4.0 amount in PHD2 (So, 16px, am I correct?)



Clearly, I have an issue here..This is not by calibration files, those lines are visible after stack - probably will be at every single frame but I can't see them.

Here is also the PHD2 log file. I can see that dithering worked, but as I am a rookie, I can't be sure how to interpreter all those infos. Any tip will be more than welcome!

Hmm, I'd say this is the 'rain' I had been talking of. You can see that the 'stripes' are in RA direction.

The pattern is made from so-called FPN, fixed pattern noise. Think of it similar as hot pixels, just that their deviation is much less. So you do not see it in a single exposure, as they are randomly distributed. But if you start displacing it in only one direction those deviating pixels will start to form the lines you see there. This is why dithering isn't really effective in RA-only guiding.

If I understand correct, for the first image dithering failed. Would really be important to know if it only claims it failed, or if the dither really did not happen. As you say it works with Stellarmate - is that indeed also with SEP and multi-star guiding?