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Collimation tools question...


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Hi there,

I am learning to do collimation using astro babys guide. I have an F5 Newtnian and mainly use it for imaging. Up till now I have just used a laser collimator but it seems that can bettered, not least because I have discovered the collimator is out of collimation itself!

I got a collimation cap and have got used to positioning and adjusting the secondary mirror with it. I have also been adjusting the primary mirror using the cap as well. In astro babys guide, it suggests using a cheshire for adjusting the primary but it looks from the article that the views through the cap and the cheshire are pretty much the same, with the cheshire providing a more 'cropped' view.

My question is  'do I need a cheshire collimator or will my existing cap do the job just as well?'

Cheers, Tim.

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It will do fine.

I started with a cap, then Laser, now a Cheshire, but still use them all.

You could collimate by eye alone, then carry out a high magnification Star test on Polaris, to confirm that the optics are aligned by observing the Airy disk.

If you believe that your visual images are sharp and clear with a cap, do you need anything else?

I can collimate with either tool and achieve the same results!

Check how to collimate the laser if you want to continue using that tool, also check using a Barlow with a laser, the Laser does not need to be fully collimated if/when using a Barlow, making set-up of the Primary much easier.

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It will do fine.

Check how to collimate the laser if you want to continue using that tool, also check using a Barlow with a laser, the Laser does not need to be fully collimated if/when using a Barlow, making set-up of the Primary much easier.

Thanks Charic... How do use a barlow? (I assume just put the barlow in between the laser  and focuser?). Also why is collimation of the laser not so crucial? I have spent over an hour trying to collimate my laser. I can get the error down to less than a cm radius (on turning the laser) on a wall about four metres away, but can't get it any better than that!

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Thats about right.

Its essential to get the secondary mirror aligned beneath the focuser, with the three primary mirror clips visible.

Now using a Barlowed Laser, the laser light is diffused across the face of the primary mirror, causing the central spot on the mirror to cast a shadow, which is clearly visible on the target face of the laser tool.

Getting the shadow to surround the  target centre is much easier that chasing the laser back in to the hole?

As long as the shadow surrounds the hole on the target face, your optics will be as good as it gets......... millimetre accuracy is not essential and some folk can spend hours chasing that laser spot, and the laser itself, does not need to be properly collimated, it just needs to be on, and able to produce laser light?

I have a cheap laser, and have removed the switch  unit several times to repair the thing, as it seems to loose electrical connectivity, but I still have it working. I used the video on youtube called Collimating the collimator  by  Astronomy Shed. he creates ( replicates ) a Jig using PVC pipe ( I had loads of pipe, and have improved the strength and stability of my jig) but my laser dot at 20 feet remains a dot during any rotation of the tool, by following the method in the video.

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Just get a cheshire, its a bit more reliable and its sight tube function is great for getting the secondary mirror centred properly. Just remember to use a bit of white card/paper behind the secondary so you can ensure there is a concenteric gap around the secondary (useful to block off your primary at this stage too).

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Uranium235 mentions the Cheshire. Its a great tool, does the job, and use zero batteries, so nothing to go wrong? But so many folk give up too early with the laser, learn how to use it properly and its a great tool,

I  get good collimation from my Skyliner using any method, it just takes practice. I also remove/ / fully-offset my mirrors when I collimate, just to prove to myself that I get it right every time.

I can easily cross-check any collimation, with any method and the results remain the same, pretty good.

However, having used the eyes-alone, 35mm film cap, Laser and Cheshire, The Cheshire should be the most reliable to use once  you master the technique.  I also chose a 'long'  version Cheshire which aids  better visual accuracy with the secondary mirror?

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Thats about right.

Its essential to get the secondary mirror aligned beneath the focuser, with the three primary mirror clips visible.

Now using a Barlowed Laser, the laser light is diffused across the face of the primary mirror, causing the central spot on the mirror to cast a shadow, which is clearly visible on the target face of the laser tool.

Getting the shadow to surround the  target centre is much easier that chasing the laser back in to the hole?

As long as the shadow surrounds the hole on the target face, your optics will be as good as it gets......... millimetre accuracy is not essential and some folk can spend hours chasing that laser spot, and the laser itself, does not need to be properly collimated, it just needs to be on, and able to produce laser light?

I have a cheap laser, and have removed the switch  unit several times to repair the thing, as it seems to loose electrical connectivity, but I still have it working. I used the video on youtube called Collimating the collimator  by  Astronomy Shed. he creates ( replicates ) a Jig using PVC pipe ( I had loads of pipe, and have improved the strength and stability of my jig) but my laser dot at 20 feet remains a dot during any rotation of the tool, by following the method in the video.

Thanks again Charig... I should have waited for your reply...as it is, I read an article by Carlin and cut a little disc out and put it on my Barlow. I fiddled about for ages then realised I had to look at the disc on the barlow directly. My barlow was too short to see in the focuser so was thinking about searching for mirrors when I checked back. Your method is much easier and I have just just collimated. Now for some clear skies to test out. Hopefully tomorrow!

Hopefully this will be more accurate than chasing the laser into the hole, especially as it is not perfectly collimated. Its a bit like shining a torch down the tube and centering the shadow. Thanks. Tim. 

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...another thing, if the laser is  properly collimated, its just as easy to use the laser spot  to align the tilt of the secondary mirror, as you don't look through the focuser at any distracting mirror images. you just look down the open end of the OTA and chase the laser dot onto the primary spot, using the three set screws - Alan bolts on the secondary hub. You then would normally work from the base of the scope and align the primary mirror, chasing the laser spot yet again back into the laser hole! The Barlowed, reflected centre spot is  much quicker to align IMHO, but the real benefit is that you only need some laser light, not the best most expensive collimated device for the final check.

Some folk will differ, but eventually you will find the method best suited, for your  use.

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.........possibly the same article?    have a peek here.....    http://www.cameraconcepts.com/barlowed%20laser%20collimation.pdf

The thing I like about the Barlowed method, is that its just a quick and simple method to check the final position of the primary, especially after a short car trip to some dark site!

Not seen that article before.  Explains it really well, I will have to try it out as I have only tried the barlow laser method once and didn't appreciate the difference.  Thanks

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.........cut a little disc out and put it on my Barlow?

That puzzled me a little! If your using something like a 35mm Film-cassette case, you need a white reflective surface inside the lid to better see and create a target area?

There shouldn't be any disc in the Barlow itself? My Laser has a 45° indent cut-out, containing a target reticle engraved to the angled surface. This is where I align the reflection of the centre spot.

Here is the laser I chose, and should you wish, the link for a Cheshire......

http://www.ebay.co.uk/itm/Next-Generation-Laser-Collimator-for-Refractor-Reflector-telescopes-1-25-/380887110161

 I had some issues with the switch on my laser,  but  after a few dismantles, I fully understood how it came apart, and which way the washers, and other artefacts have to re-align, in order to work again. 
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.........cut a little disc out and put it on my Barlow?

That puzzled me a little! If your using something like a 35mm Film-cassette case, you need a white reflective surface inside the lid to better see and create a target area?

There shouldn't be any disc in the Barlow itself? My Laser has a 45° indent cut-out, containing a target reticle engraved to the angled surface. This is where I align the reflection of the centre spot.

Here is the laser I chose, and should you wish, the link for a Cheshire......

http://www.ebay.co.uk/itm/Next-Generation-Laser-Collimator-for-Refractor-Reflector-telescopes-1-25-/380887110161

 I had some issues with the switch on my laser,  but  after a few dismantles, I fully understood how it came apart, and which way the washers, and other artefacts have to re-align, in order to work again. 

I think that's the point, you have to use to Barlow to diverge the beam to see the shadow of the centre spot, and you will need a new 'target' on the return as it will be bigger than the hole that leads to the laser target

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.........cut a little disc out and put it on my Barlow?

That puzzled me a little! If your using something like a 35mm Film-cassette case, you need a white reflective surface inside the lid to better see and create a target area?

There shouldn't be any disc in the Barlow itself? My Laser has a 45° indent cut-out, containing a target reticle engraved to the angled surface. This is where I align the reflection of the centre spot.

I followed the instructions on page 4 of the article...needlessly Lol.

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That makes sense now, the Laser depicted does not appear to have the cut-out, so a  target is required! This is built using a filter, fitted  inside the Barlow. Your right!

The telescope in use is also a truss-tube? The method detailed (see the  images )  would be rather difficult to see on a solid tube,  like my Skyliner, you would probably need help, unless you have a short OTA and can adjust the primary and view the reflection inside the telescope at  the other end at the same time?

The laser I chose has the target face already installed. This is easily observed, outside the OTA when seated at the primary mirror.

In this link ( copy & paste the link )  Ralph clearly shows the benefit of the angled cut-out on the laser tool, when adjusting the primary towards the end of the video www.youtube.com/watch?v=8G98RTP6jbY

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