Discuss telescope collimation and OCAL Collimator

Hello everyone, today I create a new thread about collimation. Welcome everyone to discuss it. If I have something wrong, please correct me.

Let’s focus on the collimation of the Newtonian reflecting telescope

What kind of collimation is the correct collimation?

1、I think that the essence of all reflecting telescopes is to reflect the light collected by the Primary mirror to the eyes or the camera.

So the Primary mirror we see at the end of the eyepiece must be a circle, if not, there must be a problem with the collimation

Does the picture below meet this standard?

We can see that the Primary mirror is not a circle at all, indicating that the collimation is incorrect

2、Regarding the secondary mirror, what should the secondary mirror look like?

We believe that the secondary mirror should also be round, and only the round secondary mirror can reflect the light from the circular surface of the primary mirror most reasonably.

In the first picture, the secondary mirror looks like an ellipse. Obviously, the collimation of the secondary mirror is also wrong.

What about this picture?

Can you judge whether its collimation is correct or wrong?

The red and green circles are the reference lines made by the software, these two circles are concentric with the eyepiece

I’m sending a correct collimated picture. You can find the problem with the second picture based on this picture.

Zitat von stefan-h

Hello,

first to do- the secondary mirror must be centered and round in the focuser. To check, clamp a large sheet of paper crosswise in the tube to prevent it from looking at the primary mirror. For checking/adjustment, a Cheshire or a Concenter is helpful, or in a pinch, a cap drilled through the center of the focuser.

Then align the secondary mirror to the primary mirror. The HS must be seen centrically, this can be seen by the retaining clips of the HS or its edge.

The third step would then be to align the HS with the help of its adjustment screws so that the center marking is in the center of the image. An alignment laser can also be used for the last step.

Helpful links for this-

http://www.seeing1.de/2a_justage.html

http://www.pteng.de/astro/justage/justage.htm

and for translation - https://www.deepl.com/translator

best regards Stefan

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What you said is right, it can be seen that you are an expert in this field

Zitat von Mettling

Hello ocal,

the collimation in the last picture looks very good. The very last step would be star-checking on a medium-bright star. Polaris is quite perfect for this. Look at the star with an eyepiece and your highest possible magnification near the perfect focus. When going though the focus with your focusser the, „donut“ (the picture of the aperture with the secondary mirror and it‘s holders) should collapse into the airy disc and unfold again perfectly on the other side of the focus position.

If the donut develops some kind of tail while going though the focus, your alignment is not perfect. If the donut is elliptic and the orientation of the ellipse turns 90º inside and outside of the focus, you have astigmatism in your system.

See you:

Marcus

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Hello, welcome your reply

The star point detection can see its final result. I can correct the star point by adjusting the screw of the Primary mirror, but what should I do if there is a problem with the collimation of the secondary mirror? How to collimate by star point?