Dither Settings

[cwinstone]

I've seen a lot of advise saying dithering helps drastically with the quality of an image but there's only vague information out there for HOW to do it right!

I use Backyard Eos and PH2 and I've turned it on using default settings (1 in each) but not seen any noticeable difference in noise etc.

Im trying to find the right settings to use but how do i know what is right? 

 

Thank you to any one who can clear this up for me, I'd love to take my images to the next level.

Imaging 

Skywatcher 72ed Ed

0.85x reducer/corrector

Modded Canon 600d

 

Guiding 

RVO 32mm F/4 mini guide scope

ZWO ASI 120mm

HEQ5 pro

 

[bottletopburly]

If back yard calculates same as APT then download my spreadsheet to calculate dither , download and edit to suit your equipment you need a dither around 15 pixels https://aptforum.com/phpbb/viewtopic.php?f=19&t=3157 look down the thread for download 

[cwinstone]

32 minutes ago, bottletopburly said:

If back yard calculates same as APT then download my spreadsheet to calculate dither , download and edit to suit your equipment you need a dither around 15 pixels https://aptforum.com/phpbb/viewtopic.php?f=19&t=3157 look down the thread for download 

awesome thank you! does this look right? (I'm assuming I include the 0.85x reduction, 420 becomes 357) .  If the setting in APT/Backyard is 4 does that mean i need to have 3 in PHD2 (4x3=12) or over shoot it and have 4 in PHD2 (4x4=16)
Thanks again for helping!

[bottletopburly]

1 minute ago, cwinstone said:

awesome thank you! does this look right? (I'm assuming I include the 0.85x reduction, 420 becomes 357) .  If the setting in APT/Backyard is 4 does that mean i need to have 3 in PHD2 (4x3=12) or over shoot it and have 4 in PHD2 (4x4=16)
Thanks again for helping!

dither of 4 gives you maximum dither of 19 pixels with phd2 scale  set to 1

[KP82]

I use BYEOS too. I've read somewhere on CN before that the dithering setting in BYEOS works like this:

1 = 0.5x, 2 = 0.75x, 3 = 1x, 4 = 1.25x and 5 = 1.5x.

I've set my dithering to 3 in BYEOS and 7 in PHD2. This is to tell PHD2 to dither 7 pixels (1 * 7) for the guide camera. And my guide to imaging ratio is slightly above 2, so it's effectively doing 15px dither for my DSLR.

Edited February 20, 2021 by KP82

[cwinstone]

 

4 minutes ago, KP82 said:

I use BYEOS too. I've read somewhere on CN before that the dithering setting in BYEOS works like this:

1 = 0.5x, 2 = 0.75x, 3 = 1x, 4 = 1.25x and 5 = 1.5x.

I've set my dithering to 3 in BYEOS and 7 in PHD2. This is to tell PHD2 to dither 7 pixels (1 * 7) for the guide camera. And my guide to imaging ratio is slightly above 2, so it's effectively doing 15px dither for my DSLR.

I'm finding this all very confusing sorry, for something so important the information seems to be hidden in complexity! Thanks though I'll consider this when using the above calculator!

[cwinstone]

15 minutes ago, bottletopburly said:

dither of 4 gives you maximum dither of 19 pixels with phd2 scale  set to 1

sorry if I'm being slow to catch on. If i try and get the MDD as close to 30 as I can, that means I need to set my imaging to 6? does that mean PHD2 needs to be 2 or 3 to make 12 or 18?
How do I find my guide to imaging ratio? is it 357/130=2.75?
And if KP82 is right about BYEOS  then do  i need  BYEOS =7 PHD2=3

BYEOS 7=2x, 2x2.75=5
PHD2 =3

5x3=15!

 

[KP82]

Use the following page to find out your guide to imaging ratio:

https://astronomy.tools/calculators/guidescope_suitability

The setting in BYEOS doesn't affect your guide to imaging ratio. It's a multiplier for PHD2 dithering.

[bottletopburly]

Yes you can adjust phd2 scale to suit to get right calculations 

[cwinstone]

14 minutes ago, KP82 said:

Use the following page to find out your guide to imaging ratio:

https://astronomy.tools/calculators/guidescope_suitability

The setting in BYEOS doesn't affect your guide to imaging ratio. It's a multiplier for PHD2 dithering.

the above has given me  1:2.39

So does that mean for every 1 pixel on the guide scope it will move 2.39pixels on the imaging scope?
If i want 30 pixel dither  (30/2.39=12.55) I need 4 in PHD2 (12) and 3 in BYEOS?

Thank you again for taking the time to explain this to me

[cwinstone]

i got the 4 from this PHD2 scale
 

Dither Level   |   Pixels

---------------       ---------

1       -             +/-  0.5  x  Dither Scale   

2       -             +/-  1.0  x  Dither Scale

3       -             +/-  2.0  x  Dither Scale  

4       -             +/-  3.0  x  Dither Scale

5       -             +/-  5.0  x  Dither Scale

[michael8554]

12 hours ago, cwinstone said:

So does that mean for every 1 pixel on the guide scope it will move 2.39pixels on the imaging scope?
If i want 30 pixel dither  (30/2.39=12.55) I need 4 in PHD2 (12) and 3 in BYEOS?

Your understanding is Bang On !

Though a Dither of about 12pixels on the DSLR is more common.

Michael

[cwinstone]

6 minutes ago, michael8554 said:

Your understanding is Bang On !

Though a Dither of about 12pixels on the DSLR is more common.

Michael

I'm getting there lol! Is 12 more common as the pixel density isn't as much as dedicated cameras?
12/2.39=5.03  so I need to make 5

PHD2 2 and BYEOS 3?

[KP82]

14 hours ago, cwinstone said:

Dither Level   |   Pixels

---------------       ---------

1       -             +/-  0.5  x  Dither Scale   

2       -             +/-  1.0  x  Dither Scale

3       -             +/-  2.0  x  Dither Scale  

4       -             +/-  3.0  x  Dither Scale

5       -             +/-  5.0  x  Dither Scale

This BYEOS dither aggressiveness mapping is different from the one I've seen before. However without knowing the official numbers I can't say which one is correct.

Based on this mapping you will need BYEOS "2" and PHD2 "5" to achieve the 5pix dithering for guide camera which translates to 12pix for the main camera with your guide to imaging ratio.

[michael8554]

The Random Dither in PHD2 varies the size and direction of dithers, so many of the dithers will be less than 12 pixels.

So a slightly higher setting than 5 = 12 pixels might be in order.

Michael

[KP82]

5 minutes ago, michael8554 said:

The Random Dither in PHD2 varies the size and direction of dithers, so many of the dithers will be less than 12 pixels.

So a slightly higher setting than 5 = 12 pixels might be in order.

Michael

Agreed. My settings were aiming for about 15 - 16pix dithering. But if the new mapping is correct, then my previous settings were actually producing 32pix dithering (way more than required).

Edited February 21, 2021 by KP82

[cwinstone]

Thank you, I'll try those settings!