Collimation tools for faster scopes?

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turboscrew
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Re: Collimation tools for faster scopes?

#21

Post by turboscrew »


Nowadays I have a laser and a Cheshire.
Using a template mage of baking paper and drilled a hole on the opposite side of of the tube from the center of the focuser. Then covered it with white electric insulation tape. If the laser hits the hole, it glows red outside. Or you can put a bright light outside and check with sight tube.

When I added the secondary offset, I also marked the height of the optical axis with narrow lines on both sides of the secondary mirror. If I turn the secondary mirror sideways, I can adjust the height such that the laser "draws" a line through the side markers.
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Re: Collimation tools for faster scopes?

#22

Post by Ngc1514 »


John Fitzgerald wrote: Thu May 06, 2021 12:41 am I use the Tectron tool set: For secondary: Sight tube, Cheshire, then Astrosystems 2" laser to hit the primary center spot, followed by the Barlowed Astrosystems 2" laser to collimate the primary. Final check of the entire system with a Tectron autocollimator.
After Tom Clark closed down Tectron, not sure the 3 tool set is available any longer. I think it’s worth its weight in gold! The booklet that came with it, “Perspectives on Collimation” by Vic Menard and Tippy D’Auria, is still available from Catseye.
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Re: Collimation tools for faster scopes?

#23

Post by Don Pensack »


And the 3 tool set from Catseye is available, and much better than the Tectron Tools.
The Tectron tools haven't been available since the early '90s.

There are scopes in which the focuser is angle to hit a secondary that is farther up the tube. These are known as "low riders".
They can be successfully collimated, so the straightness of the focuser or its perpendicularity to the tube is really unimportant so long as the secondary mirror is centered under the focuer.

Center marking a secondary is a bad idea for 2 reasons:
1) the optical axis will not hit the center of the secondary in a collimated scope--it hits a few mm above that, toward the upper end of the tube.
2) the center of the secondary is used by off axis light, unlike the primary's center, so adding a dot adds diffraction.
So it is not a good idea to center dot a secondary. It is completely unnecessary in collimation anyway.
The height of the secondary in the tube can easily be ascertained by the use of a sight tube with its pupil at the apex.

Here is an illustrated collimation tutorial I wrote some years ago you might find useful:
https://www.cloudynights.com/articles/c ... e-v4-r2599
Astronomer since 1963
Currently using a 12.5" dob and a 4" apo refractor
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