Collimating SCT with webcam

[matt]

Anyone know of any links or got info regarding this?

Ta

[Dennis]

Hi Matt

Here is how I collimate my C9.25 using the ToUcam:

• I pick a night of good seeing.
• Acquire a mag 3 or 4 star in my finder scope.
• Plug in my x2.5 PowerMate and 20mm Plossl with parfocalising ring to obtain rough focus.
• Remove 20mm Plossl and replace with ToUcam.
• Defocus the star inside and outside of focus to inspect collimation on Notebook display.
• Often, one of these defocused positions displays the diffraction patterns more clearly.
• Now for the trial and error.
• Tweak a Bob’s knob by just a small turn (make a mental note of which direction) of less than say 5 degrees and observe which way the centre spot moves in relation to the outer rings.
• Keep making these small turns of the appropriate Bob's knob(s) until the diffraction rings are concentric on the Notebook display.

Notes:

1. Star should preferably be at least 50 to 60 degrees above the horizon to minimize atmospheric scintillation.
2. I usually use an exposure of 1/100 or 1/250 sec to freeze the seeing and pump up the Brightness, Gain and Gamma settings to obtain a clear image of the diffraction rings.
3. If you need to tighten a Bob’s knob and it requires too much torque, do not proceed. Instead, back off the other two Bob’s knobs to avoid applying too much pressure to the secondary holder which may deform the secondary mirror.
4. The diffraction rings will move around the Notebook display as you tweak the collimation. A large tweak may cause the star to move off the ccd chip.

Cheers

Dennis

[iceman (Mike)]

Turn it into an article and i'll post it on the site!

[Striker (Tony)]

Tweak a Bob’s knob by just a small turn (make a mental note of which direction)

This is where I fail....I just forget which one and which way I turned it....lol

If the purpose is to collimate for photography also remember to collimate with the same optical path..such as seing I am using a DSLR I will not try to collimate through a diagonal....if you imaging using the diagonal by all means collimate through it.

I have found their is a distinct difference collimating with and without the diagonal...so make sure you use the same path as you do for imaging.

Same can be said for visual viewing.

[matt]

Awesome Dennis. Cheers very muchly.

And Mike. Definitely a "keeper" in the Articles section. good thinking 99!

By the way ... I've only just discovered in the last day or so that if you do your collimation with a diagonal in place, you have to re-do it for imaging without a diag.

Might have affected my images? Although I'm still sure my tube temp ... ambient issues have played a big part.

[Robert_T]

[quote=matt]

By the way ... I've only just discovered in the last day or so that if you do your collimation with a diagonal in place, you have to re-do it for imaging without a diag.
quote]

Matt - You can bet your booties it would have had an impact unless by some miracle you've got a perfect diagonal.

cheers,

[netwolf]

I had the same idea for my Dob, but was wondering if it could be done using a Artifical star, as then i would not have to manualy track the star while collimating. I also wonder if such a process could be automated with motors on the colimating scres etc.

Regards