5 replies to this topic

[bill.beauchemin]

I'm really at my wits end here. I've had a GSO RC6 for a while and no issues co.limating it. I recently upgraded to a RC8 I have tried to cullimate it for four nights. I'm using a ocal and a Howie laser. I keep getting the star test to the lower left really bad. Trying to center it doesn't work. I can't get the secondary to shift towards center.

 

Today I set the primary adjusters to the bottom to a start8ng point. J then adjusted using the Howie then switched to the ocal and adjusted the secondary. I switched back and fourth untill the ocal had what I thought was centered. 

 

First question. With the ocal I see a black dot and the doughnut. Which needs to be centered?

 

This was my latest bench collimation

 

 

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[syam]

With these cheap RC scopes, you cannot really properly collimate the scope by using the mechanical markers (edge of the mirror, center dot, baffle etc), becausu the mechanical features are far from being perfect.  Instead you should use optical-only collimation. To do it on the cheap, you can use the well tested DSI method which uses out-of-focus images of real stars.

 

I slightly modified the DSI method, and it was easier to collimate:

 

https://www.cloudyni.../#entry12907264

 

Specifically, I used inside-focus images of stars (instead of outside-focus, as is in the DSI method). Also, using a full frame sensor (Canon 6D in my case) greatly simplifies things, as it magnifies all deviations from the perfect collimation.

Edited by syam, 11 May 2025 - 12:14 PM.

[KLWalsh]

I collimated my RC8 through a series of steps.
First using a cheshire eyepiece and a laser collimator going back and forth between them a few times.
Then I set a first suface mirror against the front, covering about 2/5ths of the opening, and used the ‘hall of mirrors’ effect to further tweak the centering. This I did in the daytime.
A star test that night still showed some asymmetry, so I bought a tri-bahtinov mask and tried it.
First I focused on a bright star with a standard bahtinov mask, then switched to the tri-bahtinov mask. I only needed to tweak the screws on the secondary, and it only took me about 20 minutes to get it well collimated. I was using my Canon APS-C mirrorless camera to watch the diffraction patterns. Every time I tweaked one of the screws I tapped the mount’s hand control to recenter the star in the center of the camera’s sensor.
After the diffractions were all symmetric I took a photo of the Beehive star cluster and saw acceptably round stars across the image.

Edited by KLWalsh, 14 May 2025 - 08:02 PM.

[Jeff Morgan]

With these cheap RC scopes, you cannot really properly collimate the scope by using the mechanical markers (edge of the mirror, center dot, baffle etc), becausu the mechanical features are far from being perfect.  Instead you should use optical-only collimation. To do it on the cheap, you can use the well tested DSI method which uses out-of-focus images of real stars.

 

I slightly modified the DSI method, and it was easier to collimate:

 

https://www.cloudyni.../#entry12907264

 

Specifically, I used inside-focus images of stars (instead of outside-focus, as is in the DSI method). Also, using a full frame sensor (Canon 6D in my case) greatly simplifies things, as it magnifies all deviations from the perfect collimation.

 

I tried the Takahashi collimation scope on my iOptron 10” truss. It gets it close.

 

Then I tried the SkyWave CT collimation software. At the risk of oversimplifying SkyWave, one could think of it as a quantitative implementation of the DSI method. And an implementation that does not require excellent seeing.

 

SkyWave was a substantial improvement over qualitative Mk I eyeball methods of judging centered rings and reflections in the Takahashi collimation scope.

 

I may not keep the iOptron, but I will be using SkyWave on my Takahashi Epsilon. 

[quilty]

1. HOM (Hall of Mirrors) iteratively, 1. primary 2. sec. mirror
2. HOM
3. HOM
4. final adjustment sec. mirror only at high pow at the star

Ritchie-Cretin

Where I am things use to go haywire. But I can't be anywhere anytime, my bad

Edited by quilty, 15 May 2025 - 06:59 AM.

[orthofun]

This video might help.

 

https://www.youtube....h?v=aLwTkyJZM1Y