Dithering with 1000D-scale setting

[bottletopburly]

Does anyone know the preferred dither scale setting in phd2 when using a canon 1000D.

[michael8554]

The dither scales in PHD2 set the number of guide camera pixels the mount is dithered, not the imaging camera.

So you need to work out the ratio, guide arcsecs per pixel to imager arcsecs per pixel.

This figure will be unique for each setup, so only saying you have a 1000D won't  work.

So if your ratio is 3 and you want to dither the imager 12 pixels you would set PHD2 to dither 12/3 = 4 pixels.

Michael 

[bottletopburly]

5 hours ago, michael8554 said:

The dither scales in PHD2 set the number of guide camera pixels the mount is dithered, not the imaging camera.

So you need to work out the ratio, guide arcsecs per pixel to imager arcsecs per pixel.

This figure will be unique for each setup, so only saying you have a 1000D won't  work.

So if your ratio is 3 and you want to dither the imager 12 pixels you would set PHD2 to dither 12/3 = 4 pixels.

Michael 

Guide camera is a qhy5L-11( pixel ratio 3.75 )  on a qhy mini guide scope 130mm fl ,no idea what I’m supposed to be working out arc secs per pixel .

[michael8554]

Well the guide scale (3.75um pixels and 130mm FL) is 5.95arc secs per pixel

Imaging scale with 200P/200PDS (1000mm) and 1000D (5.7um pixels) is 1.18arc secs per pixel

So every one pixel movement from the guidecam will move the DSLR 5.95/1.18 = 5 pixels approx

(So to guide to less than one pixel imaging accuracy you need PHD2's sub pixel guiding ability)

So a multiplier value of 2 in PHD2 would give you a dither of about 10 pixels.

For the 127 Mak (1540mm) it's 0.76 arcsecs per pixel

This time the ratio is 1.18/0.76 = 1.6 pixels approx.

So a value of 6 would give you a Dither of about 10 pixels.

Calculator here:

https://astronomy.tools/calculators/ccd

Hope I've got my ratios the right way round !!  ............  :-> 

Michael

[bottletopburly]

1 hour ago, michael8554 said:

Well the guide scale (3.75um pixels and 130mm FL) is 5.95arc secs per pixel

Imaging scale with 200P/200PDS (1000mm) and 1000D (5.7um pixels) is 1.18arc secs per pixel

So every one pixel movement from the guidecam will move the DSLR 5.95/1.18 = 5 pixels approx

(So to guide to less than one pixel imaging accuracy you need PHD2's sub pixel guiding ability)

So a multiplier value of 2 in PHD2 would give you a dither of about 10 pixels.

For the 127 Mak (1540mm) it's 0.76 arcsecs per pixel

This time the ratio is 1.18/0.76 = 1.6 pixels approx.

So a value of 6 would give you a Dither of about 10 pixels.

Calculator here:

https://astronomy.tools/calculators/ccd

Hope I've got my ratios the right way round !!  ............  ?

Michael

Thanks for that hadn’t seen it explained how to work out the correct dither scale before ? much appreciated.

[bottletopburly]

@michael8554Should the mak not be 5.95/0.76 =7.8?

[michael8554]

Yes 5.95/0.76, my bad

Michael