Collimating Reflector

[rockonron]

I have read loads of articles online about collimating a reflector,

I have a laser collimator and as far as I can tell I am doing everything that is required.

However I spend ages getting everything lined up and all looks well. But if i remove and then immediately reseat the collimator it shows up as out of line again both on the primary and the collimation target.

It is incredibly frustrating as I am not sure what i am doing wrong. 

[wookie1965]

Check your laser collimator mine although said was sold collimated was not, every time i did mine was the same as soon as collimated my laser and put it in all fell into place.

[triton1]

Have you tried making sure the collimator is collimated,mine wasn't,I placed it in a v block and pointed at a target 10ft away and slowly rotated it.It was way off so I had to adjust it using the three screws on the collimator.I also had to put one layer of masking tape around the end of the lazer so it was a tight fit in the holder.Problem sorted.

Clear skies jonn

[andyman]

If your laser is collimated it could be too much slop in the focuser which gives inconsistent results

What i did was to put insulation tape round the laser until it made a snug fit in the focuser

Hope that helps

[andyman]

Have you tried making sure the collimator is collimated,mine wasn't,I placed it in a v block and pointed at a target 10ft away and slowly rotated it.It was way off so I had to adjust it using the three screws on the collimator.I also had to put one layer of masking tape around the end of the lazer so it was a tight fit in the holder.Problem sorted.

Clear skies jonn

Sorry jonn you already stated that in your post my apologies

[rockonron]

Thanks guys, I cant believe I have being using my telescope for a year and the collimator I had was out, It was a cheapy one I got on ebay and since reading more about it, it seems that these laser collimators are not the be all and end all. So I got a Cheshire and have spent the last 3 frustrating days trying to get my telescope collimated.

I think I am my own worse enemy here as I get close then cant get the last bit to line up, so undo all my work and start again.

I suppose the main question I have is how do you ensure the Cheshire is square in the focuser. If I hold and lock it at a certain angle I get my secondary right in the centre and all looks good, but if I just place it in as I would an eyepiece the secondary looks to low. I have attached an image through the Cheshire, could someone let me know if I am on the right track. Cheers

Image

http://sdrv.ms/1bieLqd

[wookie1965]

This might help you

http://www.propermotion.com/jwreed/ATM/Collimate/Chesire.htm

[ScottS]

Barlowed laser technique! Works every time for me.

[ScottS]

Also if you're scope is "fast" it will show a bit of secondary offset.

[AlexB67]

I do not know what scope you have, but sometimes a short version of the combination tool may work better as it will sit more solidly in the focuser and not add so much weight to the system. In my little scope this little tool does the job well

http://www.ebay.co.uk/itm/Skys-Limit-Cheshire-Collimator-Newtonian-Telescopes-short-/380641200932?pt=LH_DefaultDomain_3&hash=item589ffbcb24

, but personally I find it much harder to look through and focus on the cross hairs compared to the long version. I own both however, long, short, a cap, and some tape and use all of them so I can cross check against them so I am confident they are all telling me the same thing. Perhaps sometimes an issue overlooked,  as I do not hear it mentioned often except in the more detailed articles, but no matter how good  these tools, if you have slop in the tool and slop caused by the focuser this can become a limiting factor in terms of how accurate you achievable collimation will be very quickly.  It is important to ensure that you get consistent results with whatever technique you use and to be confident that you are getting the most out of it,  without obsessing to some degree, a poor focuser for example may cause a bit of tilt on an eyepiece depending on where it sits, so you'll get some errors from that anyway. 

Finally if you like to have some fun to see how critical these things are, go out and play with collimation, bring it out under the skies and see how it affects the views, I did this when I bought my tools and it gave me a much better feel for the whole thing, it can be one of most educational things to do, remembering that tolerances can be a bit of a personal thing too  

[wookie1965]

AlexB67 is spot on if you look at the image of my focuser tube you can see where i have used a sharpening stone to flatten the the part the roller runs up as it was only touching one side causing a lot of play. Since doing this and setting the focuser up right when i put the laser in first and double checked with my Cheshire i was miles out i collimated it up and now its 100% better, their is no slack at all now the tube runs up and down a lot smoother as well.

[rockonron]

Thanks guys, I got my hands on a collimating cap and soon as I put it in, it all became clear. I think I now have my telescope collimated. Everything seems to line up. Just need a clear sky to test it out.

[Moonshane]

I think the misconception a lot of people have is not appreciating that with most (but I gather not all) cheshires, the barrel of the cheshire slides in and out of the focuser to the best position to allow you to see the whole secondary. mine is often to the hilt with no extension tube on my slow scope and halfway out plus my 2" extension in my fast scopes.

[rockonron]

I found that as well, only thing is in my focuser there was a lot play when the Cheshire was not all the way in, meaning that the crosshairs were not always in the same place. I found that using a combination of the cap and Cheshire fully inserted I was better able to line all up