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Collimating the collimator


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I came across one of the Astronomyshed videos on Youtube discussing the potential problems with laser collimators.

I tested mine as described in the video and found it circling well outside the centre marker on the primary.

I dug out the rubber compound protecting the allen screws and then started tweaking....not as easy as the video says. Took me an hour and a half but when I retested it the beam stayed within or just on the edge of the central marker.

Now I just need a clear night..... :Envy:

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You want to make sure your comfy when collimating these.I sat in a chair with a v-block clamped in a workmate aimed at a target on the far wall of my living room 3m away,3* the focal length of my scope,took an hour but well worth it.

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Is a Cheshire much easier to use?

I find a Cheshire easier to use in daylight, and it can also be used as a sight-tube, for positioning the secondary. It's my main collimation tool.

A laser is handy in the dark - but I find it's difficult to get repeatable results with mine. It's very sensitive to it's position in the focusser. I've tried the barlowed laser technique - and I'm just not sure about that, though that's mainly 'cos I'm not sure I trust the laser.

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Having just got into the Dob' camp I am learning even more arcane language....and new techniques that are needed to keep stuff sweet. Thanks All for the other suggestions..

Is a Cheshire much easier to use?

If you want to try one mine is like new, i have a couple of laser types that are accurate, could never get on with the cheshire.......

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It took me a lot longer than 1 hour to collimate my collimator. I made a V support first, but really struggled to get it aligned. In the end I found it easier to put it in the focuser and rotate it around, adjusting it until the beam didn't move in a circle anymore.

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........take it out of the bin and try the Barlowed Laser as Bart mentions. Works great to check the final position of the primary mirror. The laser just needs to be on?

Cross checking, I obtain good collimation whatever method I use, 35mm cap, Laser, Barlowed Laser, or Cheshire. I prefer to use the Cheshire sight tube from the outset, but always have the Barlow and Laser with me for a quick final check. The laser still has some use, or donate it to someone! Unless the bin-men have been?

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........take it out of the bin and try the Barlowed Laser as Bart mentions. Works great to check the final position of the primary mirror. The laser just needs to be on?

Cross checking, I obtain good collimation whatever method I use, 35mm cap, Laser, Barlowed Laser, or Cheshire. I prefer to use the Cheshire sight tube from the outset, but always have the Barlow and Laser with me for a quick final check. The laser still has some use, or donate it to someone! Unless the bin-men have been?

Laser is gone now threw it away months ago.

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I know my laser is ever so slightly out of whack - but not by much. Rotating the laser in the focuser makes the spot circle the inner edge of the center ring on the primary.  Its certainly good enough for getting things pretty much in the region of 95% collimated. As the laser goes in the focuser in the same orientation each time, i know the result I get is repeatable. 

I then do a star test - something you should do even with a cheshire  :grin:

With my 'not quite collimated' laser, I generally need one minor tweak on the uppermost primary knob and its spot on with the star test.

Dont get yourself too wound up about getting the laser perfectly collimated, star test fixes all and is very easy to do and by far the most accurate!

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