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Anyone use camera for collimation?

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#1 Stew57

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Posted 04 November 2013 - 02:50 PM

I used my mallincam for collimation last time. Is there any reason that this would be detrimental? Anything to be aware of using this method?

#2 GlennLeDrew

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Posted 04 November 2013 - 04:32 PM

For the purpose of imaging, using the same camera to collimate is generally the better method. For then you are able to balance off-axis aberrations. Especially if for some reason the camera or its mounting is not perpendicular to the optical axis.

#3 shawnhar

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Posted 04 November 2013 - 05:02 PM

I use my Canon dslr and EOS Utility live view, zoomed to 200%. I can look at the image on the laptop while adjusting the screws.

#4 Mert

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Posted 04 November 2013 - 05:16 PM

Yes I use/used all of the webcam's I've had ever since!
Starting with some weird Hercules webcam, then SPC900
after that DFK21 and right now ASI120MC.
Works great when you can see on screen what's happening.
Also strongly recomended to use Metaguide for
collimation, excellent tool!!

#5 WesC

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Posted 04 November 2013 - 05:25 PM

I'm planning on getting an inexpensive planetary cam and this would be a great additional use for it!

#6 Ed Wiley

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Posted 04 November 2013 - 10:15 PM

I use a DMK 21 and Metaguide for "semi-fine" collimation at F20-F50 (depending on scope) and then tweak it on a star if I happen to have good seeing. The advantage of Metaguide is that you can get real close in average seeing. But nothing beats a star tweak at the end.

Ed

#7 *skyguy*

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Posted 04 November 2013 - 10:30 PM

The freeware program ... MetaGuide ... can collimate a telescope using a camera and it's also a very capable autoguiding program:

MetaGuide

#8 Stew57

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Posted 05 November 2013 - 12:20 AM

Thanks!

#9 JBOU

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Posted 05 November 2013 - 11:12 AM

Other than finding a way to attach it, are there any other modification that need to be made to a regular PC webcam for use with MetaGuide (for collimation?

Jim

#10 dragonslayer1

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Posted 05 November 2013 - 01:35 PM

Hey Wes,
check out this site for guide/video cam
http://mallincam.tripod.com/id64.html
Kasey

#11 Ed Wiley

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Posted 05 November 2013 - 10:33 PM

Re: Attachment. You just stick in the scope, you have to have a nose piece, of course and connect to your PC. Also, check what cameras are supported before purchase. If you use Metaguide you need to boost the "F" to a minimum of F20 so that you can see the Airy disk. With a SCT that would be a 2x barlow (although I have been known to go F/50; more "F" is better than less). With my F/4 that's a 5x barlow.

I haven't tried Metaguide for guiding, but am going to try it in the future.

Ed

#12 Nicola

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Posted 08 November 2013 - 06:07 AM

A side question regarding collimation with MetaGuide: is it really necessary to put a barlow or I can make the adjustment at prime focus?

#13 freestar8n

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Posted 08 November 2013 - 06:37 AM

Hi-

In the past, if you wanted to resolve the Airy pattern, you needed to increase the f/number so it was large enough on the scale of the pixels. This is because the spatial size of the Airy pattern only depends on f/number (and wavelength). For green light, f/10, and pixels about 7um, this demanded using a barlow.

But with the new cmos cameras with small pixels, about 3.75um, you get much better spatial resolution. If you combine that with a red or infra-red filter, the Airy pattern is much larger and can be resolved at f/10 without a barlow. For faster systems you might still need a barlow, but you can always try and see.

But things are different now because you can use a red or IR filter in combination with small pixels - and still be using a real star overhead, and the full aperture of the optical system to collimate based on the in-focus Airy pattern.

Frank

#14 freestar8n

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Posted 08 November 2013 - 06:53 AM

I should add that with MetaGuide, you can still collimate even if the Airy pattern isn't resolved, because it provides a "coma dot" that lets you see where any tiny comatic blur is present in the star spot. You collimate by adjusting the screws to move the star in the direction of the dot - and if you have autoguiding setup, MG will automatically re-center the star in the view. Eventually the dot just appears to move randomly over the center of the star - and you are collimated.

So - you don't need to resolve the Airy pattern to collimate, but no matter what I would use a real star in-focus as the final indicator that you are collimated. This is described in most manuals that come with a telescope, and textbooks describing collimation.

Frank






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