How to work out dithering settings for a DSLR in APT and PHD2?

[bluesilver]

Hi,  So i have been guiding without dithering mainly because i didn't and still don't know how to correct set it up

So my equipment is:

Imaging camera - Canon 600D ( specs say Pixel width and height are both 4.3um

Main scope is 1200mm focal length aperture 150mm

Guide camera is ASI290mm mini ( specs tell me it is pixel size is 2.9um )

Guide scope is 240mm focal length aperture 60mm

From what i have read doing a bit of research is that they recommend a setting of 12 for dithering distance in APT

But i am trying to work out how to get to these numbers,  ( I guess i just like doing things the hard way )

Mainly want to know how to work it all out if i change to a dedicated Astro camera i can then go back and work out a correct dither for that when and if the time comes.

 

So some just say leave the scale setting in PHD2 to 1 and just set the dithering distance to 12 in APT,  that is all good,  but would be really nice to know how these numbers are come by.

I have played around with the settings in astronomy tool https://astronomy.tools/calculators/ccd

I put my camera pixel size in ( 4.3 ) and telescope focal length ( 1200 ) and get a figure of  0.74 

I then put my guide camera pixel size in ( 2.9 ) and guide scope focal length ( 240 ) and get a figure of 2.49

 

That is about as far as i can get with my understanding,  not really sure what those final numbers mean and how i am suppose to use them.

 

If anyone can please help me out here,  it would be greatly appreciated.

Thanks.

 

 

 

 

 

[Seelive]

35 minutes ago, bluesilver said:

... I have played around with the settings in astronomy tool https://astronomy.tools/calculators/ccd

I put my camera pixel size in ( 4.3 ) and telescope focal length ( 1200 ) and get a figure of  0.74 

I then put my guide camera pixel size in ( 2.9 ) and guide scope focal length ( 240 ) and get a figure of 2.49 ...
 

Those are the pixel resolutions in arcsecs, so each pixel of your camera covers 0.74 arcsec of the sky, whereas a pixel of your guide camera covers 2.49 arcsec.  The approximate formula is:

Resolution  = 206 x pixel size / focal length

Where resolution is in arcsec, pixel size is in um and focal length in mm.

[michael8554]

I think we nailed all this in your Cloudy Nights post, so why do you want us to go through it all again ?

Michael

[bluesilver]

Apologies Michael,   Not really nailed it,  Just trying to work out actually how to get the correct numbers,

You did give me a link and the formula but part of it i could work out how you got the numbers and i didn't really get to find out how

You are correct though in that we went over pretty much all of it,  just the main part of working it out i was asking about here.

Seelive has got the answers i was looking for,  combined with the answers on cloudy nights i think that has tided up the loose ends.

[michael8554]

14 hours ago, bluesilver said:

You did give me a link and the formula but part of it i could work out how you got the numbers and i didn't really get to find out how

Find out how ........... what ?

You got the numbers yourself using the calculator link.

Seelive quoted the formula that calculator uses.

I explained on CN how those figures give a ratio that needs to be applied to PHD2, to move the imaging camera 12 pixels.

It seems some software allows you to enter 12 pixels and that works, with PHD2 set to multiply by 1.0.

Michael

 

[bottletopburly]

On 31/05/2021 at 07:15, bluesilver said:

Hi,  So i have been guiding without dithering mainly because i didn't and still don't know how to correct set it up

So my equipment is:

Imaging camera - Canon 600D ( specs say Pixel width and height are both 4.3um

Main scope is 1200mm focal length aperture 150mm

Guide camera is ASI290mm mini ( specs tell me it is pixel size is 2.9um )

Guide scope is 240mm focal length aperture 60mm

From what i have read doing a bit of research is that they recommend a setting of 12 for dithering distance in APT

But i am trying to work out how to get to these numbers,  ( I guess i just like doing things the hard way )

Mainly want to know how to work it all out if i change to a dedicated Astro camera i can then go back and work out a correct dither for that when and if the time comes.

 

So some just say leave the scale setting in PHD2 to 1 and just set the dithering distance to 12 in APT,  that is all good,  but would be really nice to know how these numbers are come by.

I have played around with the settings in astronomy tool https://astronomy.tools/calculators/ccd

I put my camera pixel size in ( 4.3 ) and telescope focal length ( 1200 ) and get a figure of  0.74 

I then put my guide camera pixel size in ( 2.9 ) and guide scope focal length ( 240 ) and get a figure of 2.49

 

That is about as far as i can get with my understanding,  not really sure what those final numbers mean and how i am suppose to use them.

 

If anyone can please help me out here,  it would be greatly appreciated.

Thanks.

Set Apt to 2 ,phd2 to 1  to give a maximum dither distance of 13 pixels