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Can you dither without guiding?

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11 replies to this topic

#1 primeshooter

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Posted 25 November 2021 - 03:39 PM

Using a star adventurer 2i and a DSLR / lenses? I use the App and noticed the setting...


Edited by primeshooter, 25 November 2021 - 03:39 PM.


#2 Dynan

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Posted 25 November 2021 - 04:54 PM

Yes you can, and it's a good thing to do. In SGP there are setting for dither without guiding also.


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#3 primeshooter

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Posted 25 November 2021 - 05:26 PM

Yes you can, and it's a good thing to do. In SGP there are setting for dither without guiding also.

So just go into the software on my star adventurer app and set it to dither every 3 frames or so and that is it? Does it affect how I work the data through DSS?



#4 Dynan

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Posted 25 November 2021 - 10:44 PM

I dither each frame, which may be overdoing it. I have the old mind-set of, 'If some is good, more is better'...[smile]

 

It shouldn't affect you processing unless you have too aggressive a dither setting. You don't want the image marching out of the FOV. I use a medium setting (not sure what that is in terms of pixels) in SGP with a random pattern. While this necessitates a crop around the edges, it never been enough to compromise an image.

 

The old adage "Dither or Die" (which may not be valid in all situations) convinced me to make sure I dither. I've seen too many nice images ruined by what is called 'walking noise'...a streaky pattern that is hard (if not impossible) to process out.

 

Just make sure you have enough 'settling time' after the dither. A few seconds should suffice. It's a small time fee for best results.



#5 primeshooter

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Posted 26 November 2021 - 07:01 AM

I dither each frame, which may be overdoing it. I have the old mind-set of, 'If some is good, more is better'...[smile]

 

It shouldn't affect you processing unless you have too aggressive a dither setting. You don't want the image marching out of the FOV. I use a medium setting (not sure what that is in terms of pixels) in SGP with a random pattern. While this necessitates a crop around the edges, it never been enough to compromise an image.

 

The old adage "Dither or Die" (which may not be valid in all situations) convinced me to make sure I dither. I've seen too many nice images ruined by what is called 'walking noise'...a streaky pattern that is hard (if not impossible) to process out.

 

Just make sure you have enough 'settling time' after the dither. A few seconds should suffice. It's a small time fee for best results.

Thanks for the advice so far. On the SA app I just have a dithering range (arcmin) option. What would you put there?

 

Someone has posted this on a reddit - If you're not guiding, your tracking will not be precise enough to need dithering. You'll have a bunch of problems but dithering won't be one of them.

 

True or false?


Edited by primeshooter, 26 November 2021 - 08:15 AM.


#6 primeshooter

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Posted 26 November 2021 - 07:32 AM

Should I drizzle also then while I am at it in DSS?



#7 8472

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Posted 26 November 2021 - 08:46 AM

Thanks for the advice so far. On the SA app I just have a dithering range (arcmin) option. What would you put there?

 

Someone has posted this on a reddit - If you're not guiding, your tracking will not be precise enough to need dithering. You'll have a bunch of problems but dithering won't be one of them.

 

True or false?

 

False


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#8 crackout

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Posted 26 November 2021 - 10:08 AM

You definitely have to find out the settle time of your mount after a dither pulse.
Depending on your desired accuracy and mount, this could take from several seconds to even minutes.
When guiding, you usually define a settle condition (total RMS below x arc/px for y seconds) after which the next sub starts.

Edited by crackout, 26 November 2021 - 10:10 AM.


#9 whwang

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Posted 26 November 2021 - 11:50 AM

False


Agree. If one doesn’t guide, the tracking errors are usually not random enough and can cause walking noise.
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#10 calypsob

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Posted 26 November 2021 - 12:23 PM

With DSLR, try and select the most aggressive dither option if you are shooting wide field, it helps rejection go a long ways 



#11 niaz

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Posted 26 November 2021 - 01:12 PM

for the dithering range, use this formula

d = 35*p/f

p= pixel size of your sensor in um

f= focal length of the lens in mm

 

e.g with my EOS R with pixel size 5.36 um and 400mm lens

 

dithering range = (35*5.36) / 400

                         = 187.6 /400

                         = 0.469

 

in the SAM app if you need decimal places just put 0 first and then edit it and the decimal point will appear.


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#12 Frosth76

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Posted Yesterday, 02:41 AM

I just started out and after some research I made a video regarding dithering that might be useful to some of you out there. I use a Canon 60D DSLR (unmodified).
https://www.youtube....h?v=YcBOJuKDoMQ


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