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Glatter laser collimator with spot and circle attachments

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First tests with a Glatter laser collimator (635nm) and the circular ring attachment on an RC.

I have been using my Glatter collimator with the standard attachment producing a small spot for a while to align the focuser and the secondary, then a Cheshire to align the primary with reasonable success. But I’ve never got consistent results so I thought I’d get the circular ring attachment for the Glatter 635nm and see what that would do to help.

My RC is observatory mounted but it is taken on and off the mount quite often and that’s when I find collimation can slip a little.

First as before I’ve used the Glatter with the standard attachment producing a small dot to confirm/adjust the secondary mirror so the reflected beam goes straight back to the source. Followed by the circles attachment, the ring pattern being reflected onto the face of the primary mirror and the rings show up well (courtesy of the small flecks of dust etc) making it easy to check the secondary alignment.

Note: If the ring pattern is not cenetred on the primary after using the small dot attachment first then the secondary mirror may be out of centre within the tube. To correct this it will need repeated use of the dot and circle attachments. (the dot to adjust the focuser/secondary alignment, the circles to check that the secondary is now aligned by producing a centered reflection.

The primary will now project/reflect the ring pattern onto a screen/wall etc where a large diffuse illuminated circle will be seen with the vane shadows (4 in my case). Inside that will be a dark circular patch. Also you will see the ring pattern and the central shadow of the secondary holder and the secondary support vanes.

The object now is to tilt the primary mirror so that the ring pattern is central, here the two sets of vane shadows are really helpfully as they can be aligned against each other. Any misalignment is shown as an off-set in the vane shadows.

Hope the schematic helps. 

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attachicon.gifRC Glatter alignment_s.jpg

First tests with a Glatter laser collimator (635nm) and the circular ring attachment on an RC.

I have been using my Glatter collimator with the standard attachment producing a small spot for a while to align the focuser and the secondary, then a Cheshire to align the primary with reasonable success. But I’ve never got consistent results so I thought I’d get the circular ring attachment for the Glatter 635nm and see what that would do to help.

My RC is observatory mounted but it is taken on and off the mount quite often and that’s when I find collimation can slip a little.

First as before I’ve used the Glatter with the standard attachment producing a small dot to confirm/adjust the secondary mirror so the reflected beam goes straight back to the source. Followed by the circles attachment, the ring pattern being reflected onto the face of the primary mirror and the rings show up well (courtesy of the small flecks of dust etc) making it easy to check the secondary alignment.

Note: If the ring pattern is not cenetred on the primary after using the small dot attachment first then the secondary mirror may be out of centre within the tube. To correct this it will need repeated use of the dot and circle attachments. (the dot to adjust the focuser/secondary alignment, the circles to check that the secondary is now aligned by producing a centered reflection.

The primary will now project/reflect the ring pattern onto a screen/wall etc where a large diffuse illuminated circle will be seen with the vane shadows (4 in my case). Inside that will be a dark circular patch. Also you will see the ring pattern and the central shadow of the secondary holder and the secondary support vanes.

The object now is to tilt the primary mirror so that the ring pattern is central, here the two sets of vane shadows are really helpfully as they can be aligned against each other. Any misalignment is shown as an off-set in the vane shadows.

Hope the schematic helps. 

Update to the above:

The schematics have been based on testing a 10-inch skeleton tubed RC. I used the Glatter and attachments on my 8 in solid wall RC and found that the outer diffuse area and the associated spider-vane shadows were not seen so I had to work on just centering the ring pattern. The ring pattern will expand/contract with the focuser being moved out/in respectively so this helps in positioning the outer/inner bright rings against either the outer shadow edge of the primary or the inner shadow of the secondary holder.

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". . this helps in positioning the outer/inner bright rings against either the outer shadow edge of the primary or the inner shadow of the secondary holder."

  Hi Francis,

  Thanks for this interesting collimation report. When the primary is adjusted  by observing the projection on a surface in front of the scope, I believe what should be looked for is concentricity of the innermost visible ring with respect to the circular shadow of the secondary. Actually, it is the shadow of the secondary baffle, so one should confirm that the baffle is concentric with the secondary mirror edge.

As far as I know, (and I have no experience collimating these R/Cs), the projected circle that represents the primary edge will move together with the ring pattern when the primary is adjusted.

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Howie - thanks for the comments.

Here's a couple of images to show what I'm seeing....

First image shows collimation set (as I judge it) with everything concentric

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Second image is with one of the primary adjustment knobs altered taking the 'ring pattern' off centre and revealing the fixed shadow and fixed vane pattern commented on earlier

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I have marked the observatory wall with some small 'tick' marks just to add fixed points of reference.

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Wow, Francis, you  may have innovated the best procedure anyone has seen for laser collimation of these R/Cs . I'm itching to get my hands on one of these scopes to replicate your method. I'm headed to the Stellafane star party this week, and I'll  be cruising the observing fields looking for a willing victim. Thank you !

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Forgot  to add something, but you can't do corrections and editing post facto here like you can on Cloudy Nights, so I'm posting again.

From your misaligned primary image, as I had surmised, it looks like the projection of the primary edge moves together with the ring pattern.

The outer diffuse circle though is the most novel part to me. I would like to know its origin. I't's interesting that you did not get it with the closed tube versus the truss tube scope.

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Forgot  to add something, but you can't do corrections and editing post facto here like you can on Cloudy Nights, so I'm posting again.

From your misaligned primary image, as I had surmised, it looks like the projection of the primary edge moves together with the ring pattern.

The outer diffuse circle though is the most novel part to me. I would like to know its origin. I't's interesting that you did not get it with the closed tube versus the truss tube scope.

Howie,

I think the origin of the outer diffusion might be where the expanding conical light beam from the laser expands out past the secondary housing directly to the wall/screen without being reflected to the primary. The light reflected from the primary is then superimposed on the diffused pattern which is why one is fixed and the other moves...

post-14748-0-54035100-1405848187_thumb.j

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Hi Francis,   I believe you have it correct, and I was thinking the same thing. Thanks for your excellent diagram showing that. It could be confirmed by moving a piece of white paper held in the beam towards or away from the the projection on the wall. The outer diffuse ring should be seen to be diverging, whearas the inner projection will be collimated (all parallel rays),and will not change size.

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Hello Francis,

Does  the circular attachment suit a types of telescopes or is it more suitable for one type more that the others?

S.

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