Dithering

[Anthonyexmouth]

How often are you all dithering? Every sub or every X number of subs?

[iantaylor2uk]

I usually dither every 5 or 6 mins or so, so this could be as little as 2 subs (my max exposure time is usually 3 mins with an L-Enhance filter) or as many as 10 or 12 subs (if I'm down at 30 sec exposures). I also try to make sure the dither is 10 pixels on the main camera - you need to work out how many pixels this corresponds to on the guide camera.  

[Anthonyexmouth]

3 hours ago, iantaylor2uk said:

I usually dither every 5 or 6 mins or so, so this could be as little as 2 subs (my max exposure time is usually 3 mins with an L-Enhance filter) or as many as 10 or 12 subs (if I'm down at 30 sec exposures). I also try to make sure the dither is 10 pixels on the main camera - you need to work out how many pixels this corresponds to on the guide camera.  

I used to dither every sub, then went to every 5 but seen a couple of videos about drizzle integration and saying dither is essential, which I knew, but wondering if it has to be every frame. 

[licho52]

It's neither, it's about having enough shifts in a sequence, I want about 20 shifts (which is quite conservative). If plan 60 exposures and want 20 shifts then every 3, no matter what length.  OTOH if you're shooting 15-minute frames then you want to dither every time.

Typically I do 60x5min a channel and dither each 3.  If I go 60x7 min then 2.

Dithering is not costless, it's a tax on exposure time and there's a tradeoff of losing SNR to either insufficient or excessive dithering.

[ollypenrice]

You may also get some natural dither from imperfect polar alignment.

Olly

[Fegato]

Same as licho52 - I make sure I've got at least 20 dithers in a sequence. So dithers per exposure depends on how many subs I'm planning.

[Anthonyexmouth]

On 17/09/2022 at 02:17, licho52 said:

It's neither, it's about having enough shifts in a sequence, I want about 20 shifts (which is quite conservative). If plan 60 exposures and want 20 shifts then every 3, no matter what length.  OTOH if you're shooting 15-minute frames then you want to dither every time.

Typically I do 60x5min a channel and dither each 3.  If I go 60x7 min then 2.

Dithering is not costless, it's a tax on exposure time and there's a tradeoff of losing SNR to either insufficient or excessive dithering.

What do you mean by losing snr to excessive dithering? 

[Adam1234]

I usually dither every frame for narrowband, every 3 frames for R,G,B filters, and every 5 frames for luminance. 

Though the reason I dither every 3 and 5 for RGB and L is because of the larger number of frames I take compared to NB (owing to shorter exposure), and wanting to save back from imaging time

[Hawksmoor]

On 17/09/2022 at 05:39, ollypenrice said:

You may also get some natural dither from imperfect polar alignment.

Olly

Olly, as a lifelong  'dyspraxic' I have 'dithering' in built.

George in Lowestoft

[ollypenrice]

Wrong post. Sorry.

Olly

Edited September 18, 2022 by ollypenrice

[markse68]

I’ve never dithered (imaging anyway). Should I? I’m using an old kaf8300

Mark

[AstroNebulee]

I have always dithered every frame and get no issues with my zwo asi294mc pro, 72ed AzGti in eq mode. I'm hesitant to change it to every other or less. It eats up a bit of my imaging time, but that's the chance I take. 

Lee

[licho52]

15 hours ago, Anthonyexmouth said:

What do you mean by losing snr to excessive dithering? 

Loss of exposure time due to (excessive=unproductive) dithering.

[900SL]

The 20 rule is good to know. Thanks! 

 

[900SL]

On 17/09/2022 at 07:39, ollypenrice said:

You may also get some natural dither from imperfect polar alignment.

Olly

Doesn't that just give walking noise though Olly?

[RolandKol]

More often is better, but eats time.... 

so I have setup sequence in NINA to dither every 2 subs , but  the sequence runs each filter twice first and dithers after, so it saves a bit of time.