Single axis dithering

[serbiadarksky]

Hi

I hear about dithering and it reducing noise which is awesome.

The problem is I have the Star Adventurer and it is working only in RA.

Is it ok to dither the images with the arrow buttons on the side of the mount in RA only?

And how much and how? If i press the left button and later the right it is ok, but then again the left will do nothing...

[knobby]

I'm interested in this too, I've seen somewhere that single axis dither causes 'walking pattern noise' not sure though. I suggested to skywatcher via the app store about including it as an option via firmware a couple of months ago and they said they were looking into it.

[serbiadarksky]

1 minute ago, knobby said:

I'm interested in this too, I've seen somewhere that single axis dither causes 'walking pattern noise' not sure though. I suggested to skywatcher via the app store about including it as an option via firmware a couple of months ago and they said they were looking into it.

Ok, the traveling noise is happening to me even now without dithering..

So thay will make an software update to be able to dither automatically?

[knobby]

Just now, serbiadarksky said:

Ok, the traveling noise is happening to me even now without dithering..

So thay will make an software update to be able to dither automatically?

They said they are looking into it

[ollypenrice]

This strikes me as a bit surprising since you'd need pixel perfect PA for a dither in RA not to create a small dither in Dec as well. I'm happy to be enlightened as to what's happening here.

Olly

[serbiadarksky]

3 minutes ago, ollypenrice said:

This strikes me as a bit surprising since you'd need pixel perfect PA for a dither in RA not to create a small dither in Dec as well. I'm happy to be enlightened as to what's happening here.

Olly

Why?  I mean i got you but still..

[serbiadarksky]

8 minutes ago, knobby said:

They said they are looking into it

Thats not even that bad

Gonna message them too so they see that we really need it loool

[knobby]

app.support@skywatcher.com

[ollypenrice]

43 minutes ago, serbiadarksky said:

Why?  I mean i got you but still..

If your PA is perfect there will be no field rotation so a dither in RA will move the image only on one axis along the chip. But if PA isn't perfect then the frame will rotate slightly. I never worry about perfect PA. Provided I can get 30 minute subs without visible field rotation I'm happy to have a bit of accumulating rotation so that I get natural dual axis dither even while autoguiding. I run a dual rig with different sub lengths on each instrument so normal dither isn't possible.

Olly

[serbiadarksky]

1 minute ago, ollypenrice said:

If your PA is perfect there will be no field rotation so a dither in RA will move the image only on one axis along the chip. But if PA isn't perfect then the frame will rotate slightly. I never worry about perfect PA. Provided I can get 30 minute subs without visible field rotation I'm happy to have a bit of accumulating rotation so that I get natural dual axis dither even while autoguiding. I run a dual rig with different sub lengths on each instrument so normal dither isn't possible.

Olly

Oh i understand

[serbiadarksky]

@knobby

Hey man i just talked with Tony Hallas (probably you heard about him, have a nice tut how to remove the noise with dithering) about single (RA only) axis dithering, this is what he answered

"

Hi Nikola,

 

   Any dithering is better than no dithering ... the answer is yes, you can dither just in the RA.  I would do a small one in either direction, then a bigger set ... so you will have five images that can be aligned to kill the noise.

Tony"

Hope this leps a bit

If you have the SA than use the fine tunning buttons on the SA

[wimvb]

If you dither in one direction only (ok, 2 +/- ra), all subs will have an alignment difference in that direction. This will introduce "walking noise". Since for star alignment and integration, it doesn't matter in which order images where taken (addition can be in any order), you could reorder the dithered subs such that you can't distinguish from a constant drift. In a random or spiral 2-dimensional dither, you break up the linearity.

Imo, dithering requires 2 axes.

[serbiadarksky]

21 minutes ago, wimvb said:

If you dither in one direction only (ok, 2 +/- ra), all subs will have an alignment difference in that direction. This will introduce "walking noise". Since for star alignment and integration, it doesn't matter in which order images where taken (addition can be in any order), you could reorder the dithered subs such that you can't distinguish from a constant drift. In a random or spiral 2-dimensional dither, you break up the linearity.

Imo, dithering requires 2 axes.

Thanks for your reply. I do not dither and already have traveling noise..

I found a way to dither in RA with buttons on the side of the Star Adventurer and in DEC with the L bracket