Collimating a 10”Dob

[PatG]

Had a go at adjusting the collimation of a recently acquired pre-loved Orion Optics VX10L this morning. As expected, I found this not a straight forward matter / quite complicated and not sure what results I have obtained. I was using a Stella Lyra premium Cheshire / sighting tube to aid the process. Started by checking and adjusting the secondary mirror and then aligning with the primary. Any tips / advice appreciated. Also -  I found it hard to adjust the primary adjustment knobs by hand and wanted to seek recommendations for upgrading these, anyone done this and what replacement knobs are available? 

[kev100]

Can you take a photo through the cheshire or using a collimation cap? Like the attached. So we can see the issue. Can't help with the specifics on the Orion scope, Im afraid, tho ....

[PatG]

Hi Kev

Not having much luck with a good photo with phone through the Cheshire but this is about the best I could manage…

plus one straight through the focuser..

advice / thoughts appreciated.

 

[Carbon Brush]

I have collimated a few 10" & 12" newts. The biggest problem has been reaching the primary screws while looking down the sight tube. Not having gibbon length arms🤣

A further issue with pre-owned scopes is that you don't know what misalignments (beyond the mirrors) may already be there. For a example a focus tube not pointing to the centre of the secondary mirror.
My very first proper scope, coincidentally an Orion Optics newt (a new one) had 3 experienced people at a club scratching their heads for an hour before declaring it should go back.

For these reasons I start out with a (basic) laser collimator. You can easily see where the red dot lands and sort out issues that send you in circles if you think it is a simple mirror collimation problem.
For example if the dot doesn't land in the same spot on the secondary mirror when you rack focus in/out, you need to look why and fix it before moving on.

Don't forget any laser collimator needs to be checked on arrival by rotating in a V block.
You don't need a precision engineers block. Two bits of wood nailed together to make  90deg V will suffice, rotating the laser and projecting the dot to a wall.

HTH, David.

[kev100]

It's hard to be sure, but from the second pic it looks like the secondary isn't centered (see attached). As for the stiffness in the primary screws, just checking that you've loosened the lock screws (belt and braces!). Also, do measure the secondary vane lengths and adjust the secondary so they're all equal (I've been caught out by this).

You might find this useful...

Edited February 4, 2023 by kev100

[PatG]

Thanks for the tips David, I will look into getting a basic laser. 

Thanks Stu, checking the secondary veins they were indeed slightly unequal so I have adjusted. Re the primary adjustment, yes I had loosened off the lock bolts, I think the collimating bolts / knobs are stiff because they have not been used for a while perhaps, at some point, I’m going to clean the mirror so will need to remove the cell and will have a proper look at what is going on and consider better springs and upgraded adjustment knobs at that point. 

Pat 

[Spile]

I’ve written a guide which you may find of use. https://astro.catshill.com/collimation-guide/ the Cheshire eyepiece and sight tube combination tool should help you get the secondary mirror correctly placed. From the image you posted a would appear to be the same as b but c does not equal d .

[PatG]

Thanks Brett,

your guide is very helpful, I will be printing it out to help guide me me through the collimation process.👍

Pat

[Spile]

3 hours ago, PatG said:

Thanks Brett,

your guide is very helpful, I will be printing it out to help guide me me through the collimation process.👍

Pat

You are welcome Pat