collimation vocabulary

[alacant]

Just a heads up in case anyone else like myself got tangled up cross forum:

I read astrobaby's collimation guide alongside an article by the CN collimation guru. It seems that we call things differently:

astrobaby

collimation cap: old film canister with a hole

Cheshire collimator: tube with 45º surface and cross-hairs

sight tube: not used

CN

collimation cap: tube with 45º surface and cross-hairs

Cheshire collimator: tube with 45º surface

sight tube: tube with cross hairs

 

Evidently what I know as a Cheshire is in fact a combination of a sight tube (for secondary adjustment) and 45º shiny surface (for primary adjustment). So, something like this needs careful translation -e.g. I can't see the whole of the secondary through my Cheshire...

collimation cap: get the secondary under the focuser

Cheshire: get the primary donut on the cross-hairs

Cheshire: get the shiny surface on the cross-hairs

Rinse and repeat until boredom ensues.

[Moonshane]

You can see the secondary with a 'Cheshire' 

 

I tend to use the cheshire for all aspects of collimation but do have a simpler refractor type cheshire (a cheap plastic one withour cross haits) for the final collimation as it gives a simpler view.

[John]

31 minutes ago, Moonshane said:

You can see the secondary with a 'Cheshire' 

 

I tend to use the cheshire for all aspects of collimation but do have a simpler refractor type cheshire (a cheap plastic one withour cross haits) for the final collimation as it gives a simpler view.

Thats just the one that I have. Must be worth a whole £5 at most. Works very well though. I did 3 newts with it at a society night last year. The owners had been tearing their hair out with lasers, cheshires, caps etc. A couple of minutes with the above and their scopes were more or less on the nail.

 

[Jason D]

On 1/27/2017 at 01:44, alacant said:

CN

collimation cap: tube with 45º surface and cross-hairs

Just out of curiosity, do you have the link to that CN collimation article that states the above?

Jason

[alacant]

http://www.cloudynights.com/topic/498925-new-newtonians-offered-by-explore-scientific/?p=7662294

 

[Ouroboros]

My collimation vocabulary is unrepeatable on a family forum.

[Jason D]

43 minutes ago, alacant said:

http://www.cloudynights.com/topic/498925-new-newtonians-offered-by-explore-scientific/?p=7662294

 

Thanks for providing the link but unless I missed it, I did not see anywhere on that page a post by a collimation expert stating that a collimation cap is the same as a cheshire/sight-tube combo tool.

Vic Minard stated that a collimation cap works as a cheshire which is a true statement.

Many calls the typical collimation tool with a sight tube, a 45 reflective surface, and cross-hairs a "cheshire" which is the cause of confusion. The tool is really a "cheshire/sight-tube combo" tool. 

1- The sight-tube is used to align the secondary mirror under the focuser

2- The cross-hairs are used to align the focuser axis -- ensuring the  focuser axis is reflected to the center of the primary mirror

3- The pupil-hole along with the 45 -degree reflective surface are used to align the primary mirror -- this is the part of the tool that is called a "cheshire". The collimation cap works similarly.

Jason

 

[alacant]

Following the link in the link, you get to this:

http://www.cloudynights.com/topic/362763-collimation-is-about-to-make-me-dump-both-my-dobs/?p=4651412

It gets really scary after that. Best to stop reading there otherwise you'll never get any observing done at all!