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Old 31-08-2018, 07:50 PM
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Laser collimation - what am I seeing?

I'm working at getting my f/4 newt imaging again. I've always struggled collimating this thing, and picked up a Glatter laser several years ago.

The image shows the view in the focuser window of the reflected barlowed laser. I've labelled it for easier discussion.....

There is the shadow of the centre spot, which seems to be in the right spot, and the concentric lined pattern, way off centre?

I only use a small sensor on this scope, so don't need perfection, just (mostly) round stars will do!

Thanks for any help...
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Old 31-08-2018, 08:12 PM
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Does the laser dot when projected onto the primary actually hit the centre dot squarely in the middle? Looks to me like you need to adjust the secondary to get it striking the primary dead centre (using the secondary screws) then use the primary screws to centre the reflected image.

Other than that, is your spider centered?

Markus
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Old 31-08-2018, 08:13 PM
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When you remove the barlow, does the laser land in the middle of the centre spot on the primary mirror?

The image you have posted looks like the barlowed laser light is not illuminating the primary mirror evenly - ie most of the light is offset compared to the shadow of the primary centre spot.

If that is the case then it might be because your secondary mirror is not collimated. The barlowed image is to adjust the primary collimation.
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Old 31-08-2018, 08:34 PM
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Thanks gents....

Quote:
Originally Posted by Stonius View Post
Does the laser dot when projected onto the primary actually hit the centre dot squarely in the middle? Looks to me like you need to adjust the secondary to get it striking the primary dead centre (using the secondary screws) then use the primary screws to centre the reflected image.

Other than that, is your spider centered?
Laser dot hits primary in centre, yes.
I think the spider is centred? I'll check/adjust.


Quote:
Originally Posted by peter_4059 View Post
When you remove the barlow, does the laser land in the middle of the centre spot on the primary mirror?

The image you have posted looks like the barlowed laser light is not illuminating the primary mirror evenly - ie most of the light is offset compared to the shadow of the primary centre spot.

If that is the case then it might be because your secondary mirror is not collimated. The barlowed image is to adjust the primary collimation
Laser dot hits primary in centre, yes.
Should those concentric circles be centred around the centre spot shadow and centre of viewing window? That seems logical to me.
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Old 31-08-2018, 08:44 PM
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Quote:
Originally Posted by Lee View Post
Thanks gents....
Laser dot hits primary in centre, yes.
Should those concentric circles be centred around the centre spot shadow and centre of viewing window? That seems logical to me.
Can you post an image of the laser dot centered in the primary?

What is generating the concentric circles? Is that an attachment on the front of the laser? If so, you should remove this for the barlowed laser primary adjustment.

I've attached an image of my Glatter barlowed laser view of the primary. In my case I have a catseye hotspot rather than a ring on the primary so the shadow shape is different however you can see how the barlow should smear out the laser light to create the shadow centered on the hole in the tublug.
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Old 31-08-2018, 09:03 PM
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You could also rotate the barlow to check for optical misalignment in the barlow assembly.
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Old 31-08-2018, 09:09 PM
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Quote:
Originally Posted by peter_4059 View Post
Can you post an image of the laser dot centered in the primary?

What is generating the concentric circles? Is that an attachment on the front of the laser? If so, you should remove this for the barlowed laser primary adjustment.

I've attached an image of my Glatter barlowed laser view of the primary. In my case I have a catseye hotspot rather than a ring on the primary so the shadow shape is different however you can see how the barlow should smear out the laser light to create the shadow centered on the hole in the tublug.
Mmmm - I didn't know that bit came off.... yes, with that removed it looks much better - will post a pic.
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Old 31-08-2018, 09:17 PM
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Pic - no more concentric circles off centre! Primary still needs a little tweak.
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Old 31-08-2018, 09:30 PM
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That looks better. I found the concentric circle attachment not so useful for the newt. The cross hairs attachment or the small dot is ok though.
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Old 31-08-2018, 09:43 PM
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I *think the concentric circles attachments are more for Schmit cassegrains, Maks and RC scopes where the true optical axes may differ from the center of the mirrors.
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