GSO RC collimation

benklerk · #1 05-07-2016, 04:29 PM

I got given a gift. I glatter and holographic circular attachment as my GSO had bad coma.

After doing adjustments to both Primary and secondary, what do you think? I have a basic understanding of collimation.

glend (Glen) · #2 05-07-2016, 05:13 PM

That is not a good holographic diagram, you can clearky see that tye light rings on the left are thicker than the right. Basically you have something tilted. Have you gone through the basic steps of aligning the focuser with the secondary centre spot? What other tools do you have, like a Cheshire tube, or TAK collomation scope? What size RC is this?

benklerk · #3 05-07-2016, 05:27 PM

Quote:

Originally Posted by glend

That is not a good holographic diagram, you can clearky see that tye light rings on the left are thicker than the right. Basically you have something tilted. Have you gone through the basic steps of aligning the focuser with the secondary centre spot? What other tools do you have, like a Cheshire tube, or TAK collomation scope? What size RC is this?

Hi Glend

I have gone though the secondary mirror process. The reflected laser is coming back onto the main laser. My RC is a 6" scope. I do not have a cheshire tube or a TAK collomation scope. I should add, before I stared the outer ring was way of course, you could only see about 1/3 of it.

Howie Glatter · #4 09-07-2016, 08:02 AM

"That is not a good holographic diagram, you can clearky see that tye light rings on the left are thicker than the right."

That is not due to miscollimation. Because the red laser diode beam has polarization, the width of the diffracted circle lines varies from narrow to wider with a 90 degree rotation.

glend (Glen) · #5 09-07-2016, 09:17 AM

Quote:

Originally Posted by Howie Glatter

"That is not a good holographic diagram, you can clearky see that tye light rings on the left are thicker than the right."

That is not due to miscollimation. Because the red laser diode beam has polarization, the width of the diffracted circle lines varies from narrow to wider with a 90 degree rotation.

Sorry, my poor symantics, i should have been clearer and mentioned my concern as being the spacing between the light rings, which can be clearly seen to be different left to right - not the thickness of the light ring itself. I would agree that the light ring characteristics can vary as you rotate the laser but your actually looking for the spacing to be equalised and centred during rotation.

Howie Glatter · #6 09-07-2016, 10:24 PM

Projecting the concentric ring pattern on a surface in front of the scope is the last step in the laser collimation procedure. It is for adjusting the angle of the primary mirror. It will only work if all the previous alignments of the focuser and secondary mirror have been made correctly.
The only thing to look for here is concentricity of the circle projection with the secondary shadow. You can make the gap between the secondary shadow and the first ring visible outside it even all around. Actually, you are seeing the secondary baffle shadow, so the baffle must be concentric with the secondary as well. The size of the projected rings can be adjusted to make the gap narrow by racking the focuser.

> . . my concern as being the spacing between the light rings,
> which can be clearly seen to be different left to right -

I'm not sure I understand this. The uniformity of spacing between the rings is not affected by collimation adjustments, and is given by the rules of diffraction. The picture was taken at an angle to the screen, so everything, including the circles, is foreshortened left to right, and taller up and down. The concentricity may be a tiny bit off, but it's close.

glend (Glen) · #7 09-07-2016, 11:20 PM

I give up trying to help here. My comments were based on years of collimating my RC08 with various tools including the Howie Glatter Laser - obviously we are speaking different languages. Good luck Benklerk. Think I will unload my Howie Glatter Laser in the classifieds.

Howie Glatter · #8 10-07-2016, 06:32 AM

"I give up trying to help here . . Think I will unload
my Howie Glatter Laser in the classifieds."

" . . my concern as being the spacing between the light rings,
which can be clearly seen to be different left to right -"

"Basically you have something tilted."

What's tilted is the camera that took the picture, with respect to the screen. That means the left side of the screen is closer than the right in the picture. Things that are closer appear bigger (example: the spaces between the light rings).