Collimation aid

[soulearth]

Hi,
I recently discovered CCDciel's collimation tool which seems interesting to me (see here: https://www.ap-i.net/ccdciel/en/documen ... ollimation).

The operating principle of the ccdciel tool is to keep the defocused star in the center of the image by moving the ROI while the user moves the mount (RA/DEC) to find the position where the defocused star shows well concentric circles.

Once this step is done, center the star ( and in the same time the optical axis ) in the center of the sensor using the adjustment screws.

I found the method interesting and maybe not too difficult to add in sharpcap.

What do you think ?

Best regards,
soulearth

[admin]

Hi,

that's an interesting approach to collimation that I hadn't seen before

Perhaps this is possible already in SharpCap? I haven't tried this, but it might work...

1) Set camera to full resolution
2) Ensure target star is the only bright thing in view
3) Display the 'Circle' reticule and leave it in the default position (central)
4) turn on 'Planet/disk stabilization' in the processing controls - this should put the star central in the image, as it is the brightes thing in view, and keep it there as you do the RA/Dec movement stage
5) when the rings are concentric, turn off planet/disk stabilization, which will put the star back into its normal position
6) Now adjust collimation to put the star in the center of the reticule

If you get time to try this out, do let me know if it works. I will also try to use this approach the next time I have the newtonian out.

cheers,

Robin

[admin]

Hi,

I thought about this some more last night. Not sure if it (the ccdciel single star approach) can really work properly. If I get to the stage of trying to re-center the star using the collimation adjustments, I have three separate ways that I can do this

1) Collimation adjustments on primary mirror
2) Collimation adjustments on secondary mirror
3) Height, rotation and linear offset (centering) of secondary mirror

Any of these give me the flexibility to move the star around (and probably center it), actually to get proper collimation it will be a particular combination of these that are required. Now, there is an argument that good collimation is simply having an optical path through the telescope such that light rays incident at right angles to the primary mirror are collected at the center of the sensor with a light cone axis perpendicular to the sensor, which is correct as far as it goes, but what it misses out on is correct positioning of the secondary to ensure maximum illumination is reached (ie no light being lost because it's missing the secondary).

Maybe it's OK for final tweaks though...

cheers,

Robin

[soulearth]

Hi,
Gary Seronik describes this unusual method on his site, here: https://garyseronik.com/no-tools-telescope-collimation/

It's very fair, this method requires that the secondary is well positioned. Otherwise it doesn't work or badly. But it's not really a problem, normally, once settled, you don't touch the secondary mirror anymore.

This method ensures the perpendicularity and centering of the light ray only. Adjusting the full light cone is effectively impossible to do with this method. But it's already great because it is sufficient for the sharpness of the image. A slightly bad light cone centering will only cause vignetting on one side.

Otherwise, indeed with the stabilization of the planetary disc, we are not far from having all the necessary functions.
With only planetary stabilization I may have trouble knowing which way I'm going... I must try.


Best regards,

[Menno555]

Hi

I was following this until your last reactions.
This methode than is not for Schmidt Cassegrein scopes with "fixed" primary mirrors like the Meade ACF and Celestron C-series? These are collimated with the secondary only.

Menno

[soulearth]

Hello Menno555,
I don't have this type of telescope but in theory it's not a problem. If I understood correctly, you have to use the adjustment screws adapted to the model of the telescope.
Best regard,