collimating my laser collimator

[stevejack]

Hi Guys,
I have been trying to collimate my laser collimator as it was out by quite a bit when I bought it. It is a cheap(ish) Bintel collimator (by GSO).

I made a cradle, adjusted the screws until the beam was as central as I could get it - but here is the problem: It doesn't project a "dot", rather a line on the wall.
There is quite a bit of red glow around the brightest part of the line as well, and this glow is not symmetrical.

Is this caused by the beam hitting the edges of the collimator on its way out? Is there a way to fix this?

There is also a larger allen key screw towards the front of the collimator, directly opposite the angled plate - does this have something to do with it??

Any help is greatly appreciated,
Cheers,
Steve.

[erick]

Steve

That is my experience as well - they project an elongated spot rather than a nice tight circular spot. I'm fairly sure it is the performance of the little cheap laser unit they use. As long as you have the spot turning through a tight circle, it is usable. Just concentrate on the centre of whatever spot you are projecting. You can get that on the centre of the primary mirror and back on the hole in the target.

Not sure about that other grub screw. I don't have mine any more to look at it.

Eric :)

[bmitchell82]

I built my own laser collminator, and used a $8 HK cheepie. it too sends out this beam, but remember that the center dot on most reflectors is the size of a pen, im guessing for visual at least as long as you can get that laser on the primary marking and back into the front of the laser itself it doesn't matter if its a little oblong :D

One of the other things that i do is shove my collminator into a barlow, it gives a reasonably round dot thats about 4mm larger over all than the original dot. makes putting it in the circle alot easier.

This is the method i use also for doing goto aligning when i don't have my 12 mm rectical handy, i unfocus untill its a large doghnut thats about the size of the FOV of the eye piece and then make sure its even right the way around. :)

hope that helps:thumbsup:

[stevejack]

Thanks guys - I barlowed the laser this arvo after adjusting it and lined up the centre spot shadow - I'll try out the new collimation tonight and see how I go.
The cheshire view has changed now (I had to tweak the secondary a little to get the barlowed red zone over the center spot) but hopefully that's ok.

Cheers for the help
Steve

[Merlin66]

Steve,
I had exactly the same issue when making laser collimator for the spectroscope. I found one solution was to prick a VERY small hole in quite thick aluminium foil and wrap this around the front "nose" of the laser.
Tightens up the beam and gives a pretty circular image.
See:
http://www.iceinspace.com.au/index.php?id=63,500,0,0,1,0

[stevejack]

Great idea! I'll take another look and see what I can come up with

[bmitchell82]

must admit i rate that idea. :D
hit it like its hot.!

[erick]

Ken, did it take much effort to get that hole fairly accurately centred in the barrel (or is it over the end of the laser unit itself?)? On first thought, I would imagine it would need to be accurately centred to do what we want for collimation? Eric

[bmitchell82]

I wouldn't belive that it would have to be dead centered. but then again, in my laser collminator the laser is within the housing with 2 sets of 3 bolts holding it center.
very easy to collminate, put it on the V jig, twist it round and mark 3 120 degree marks, then make a line into the center, to give you the center of your circle, then its a matter of twisting the red dot to each of the 3 marks you made and then adjust so that the red dot travels towards the center mark. it took me less than 5 min to make sure mine was happy days, and i did it over a 5 meter range. it was good enough to get everything roughly lined up then i shoved the ceshire in. happy days. but the foil would give a tight round dot to work with not a slighty glowy oblong :D

[erick]

When I think through what would happen if the hole were off-centre (eg. allowing through a small spot at the end of the "sausage"), I don't think that is good. Forcing an apparent collimation of that image by the usual laser collimator adjustment process - well, I don't know, but I think there would be a problem?

[bmitchell82]

when i get the laser shooting straight, i was amazed to see that the actual body of the laser was skewed quite bad. Im guessing the more you spend the better the internal alignment is. This is why im saying that it shouldn't make a difference. Ill go home tonight and have a look and report tomorrow.

[bmitchell82]

Okay, went home last night and fiddled.!

Consensus was it changed the aperature of the laser to a great little dot with no glow around it.
Secondary consensus. alignment had not changed still bang on and not moving it actually made it easier to collminate the laser.

If you want to see what im working with, search the forums for it as i posted it a few months back

OH HAPPY DAYYY'S.... :D

[Merlin66]

The aluminium foil was wrapped over the end "nose" of the laser, the pin hole was aligned ( as far as possible with the centre of the laser aperture)
After that the pen was aligned in the holder with the six small screws by rotating it in V blocks until no movement of the spot on the wall.
Hope it helped.

[erick]

Sound like a very successful approach then! :thumbsup:

[bmitchell82]

yep merlin that is exactly what i have done! I put my V block in the vice in my workshop and then rotate it around on the far wall approximately 4-5 meters

[Starkler]

With mine the minute amount of movement needed to aim necessitated the grub screws being done up very tight.

End result was the barrel was compressed by the grub screws to the extent that the button cell batteries wont come out without a hard whack, thereby ruining the collimation :doh:

[bmitchell82]

whoopsy....

[erick]

With my GSO delux, now sold, I could get the first two out. Third required drilling a hole in the battery, inserting a screw and pulling hard! :lol: New set went in without too much agro. Recollimated and it was fine. Much prefer my HoTech with its single lithium battery.