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[mojocvh]

Right off we go!

First up References. This isn't my idea. I just found it on the 'net one day. I have taken info from a number of sources found via Google so If I have stepped on anybodies toes please contact myself or Joe and we will sort it out. OK.

So what's it all about? It's about collimating your SCT with very little effort or indeed distress.

The instructions are quite straight forwards, with a mask fitted, you go out of focus and you are left with a pattern of lines, centre and correct those lines using your secondary adjustment screws and you're done. 



Of course there are a couple of points to ponder.

If your scopes MECHANICAL primary/secondary alignment is WAY out you might have severely tilted your secondary WAY out to correct the apparent VISUAL discrepancy,  it is possible that your primary is moveable on the baffle tube or the adhesive that sticks the primary in place has started to fail. Bad News and beyond the remit of this thread BUT if you are interested [and it's no bad thing IMHO] ....

Ref. www.wilmslowastro.com/tips/c14_optics_alignment.html

.....gives some superb background into how these problems can be resolved...

Coarse alignment.

So firstly you want to check from the front of the scope that things are tickety boo.

Ref. www.bobsknobs.com/faq/faq.html#How_do_I_perform_coarse_collima

Hopefully you will be looking like

and not like this

In all but a very small number of SCT's there is no way to adjust [easily] the primary so you will have to correct your coarse collimation using the secondary adjustment screws. We will now assume that all is OKAY with the back end of the scope and that coarse collimation is good.

Duncan Masks.

OKAY I first tried to make up a Duncan style mask as detailed below.

Ref.
alpha-lyrae.co.uk/2013/12/31/schmitt-cassegrain-collimation-made-easy-using-a-duncan-mask/



I will now admit to being sup optimal when it comes to cardboard circles and scissors. I am in fact garbage at it [and that's where my efforts at DIY mask making ended up] LOL. 

So this project stalled, until one day, surfing the various  uk astro forums, I spotted an article/thread that had a reference to Laser cut Duncan Masks!!!
In fact it was a reference to Keith Morris from who I had purchased a bahatsov[sp?] mask for my C8 many moons ago, and was now producing these as well. Brilliant! 

On receipt of the mask made to the dimensions I supplied [Keith is a Meade man and his original masks are based on Meades] I was able to ensure that  not only was my secondary was centred wrt the actual tube itself but that the mask gave me the confidence [of finding proper collimation again] to loosen then re torque ALL my bob's knobs to the same "value" whilst tightening up collimation.
On the downside, I had to use a 10mm eyepiece with a barlow  to give me the curved lines, thus they were attenuated by all that glass....

Minor points aside this method works and is a great boon for us SCT owners, even for that little bit of confidence boosting re collimation.

cheers and all the best

Mo.

PS I almost forgot. If you get hold of a 35mm film cannister [yes] you can centre the secondary holder by simply adding a pinhole peep at the rear of the OTA and looking UP the baffle for extra reassurance.
 
Ref. www.wilmslowastro.com/tips/c14_optics_alignment.html    down at the bottom of the list...

[Chicago Astronomer Joe]

Andy...

This is encouraging.

I have requested from our Chicago Astronomer expert master craftsman, Rick....to make me one on his laser cut machine.

He has already done so and I am ready to pick it up in just a few hours.

I will post the full series of pics later, but I am anxious to read on your success with this mask.

[mojocvh]

OK just sorted that duff link to www.wilmslowastro.com/tips/c14_optics_alignment.html for the further alignment info bit.

Yeah bit of work to do to get it to fit 100%, I used strips of thin self adhesive electrical insulating tape on each "arm" to snug it down nicely in finest amateur astronomer traditions.




Of course it's been cloudy whenever I have been around since it's initial first light, but hey ho.

[Chicago Astronomer Joe]

Chicago Astronomer Joe's Collimating Duncan Mask

I had a short period of available time, on a clear sky.....to test out the Collimating mask that Chicago Astronomer Rick laser cut for me at my request...several really...




Full report soon, but it does work, (displaying the semi-circle lines shown above), but it also reveals flaws that need to be addressed...a good thing.

More later, with pics...when time permits.

[patrickm]

Joe, do you think Rick could be talked into making one for 9.25" with some cash? Too cool!