Laser alignment question using V blocks

[pat]

I've read that V blocks are used for checking the alignment and collimation of the laser. I made one out of nails,per instructions I found for my Orion laser. It was misaligned by 3mm. Now I've read from Hotech that these V blocks are not accurate. Could someone please explain. Pat

[laser_jock99]

Laser collimators are renknowned for often being misaligned to the axis of their own holders. If you start trying to collimate before checking this it will make your collimation much worse. This is why in some ways the simpler Cheshire Collimator is preffered.

If you spin your laser collimator around in a vee block (a proper enginnering one is preffered) you should not see any precession of the beam spot on, say a nearby wall. If there is- send it back (a few higher end models are user alignable). I have had to reject two, cheap Chinese collimators because of this fault. Either way- it's best to get a good, rough alignment with a Cheshire type before comencing laser fine tune, then re-check with the Cheshire.

[knobby]

Not fact but just my opinion ... V blocks or nails are accurate if the barrel is the same outside diameter at each end , ideally the v needs to be holding the laser at the end where it fits into the scope only ... Not quite sure how to put it into words ,but I know what I mean .

I can feel a drawing coming on when I het home tonight

[Peter Drew]

V blocks are inherently accurate, however if the 1.25 nosepiece is not concentric to the laser body, inaccuracies could creep in as this is the part from which the collimation procedure is judged.

[Tinker1947]

I have a Baader which doesn't lend itself to V-Blocks due to its shape, but i do have a lathe and pointing it so the laser comes out the gearbox end @ 12' its no more than its own diameter out. So if you don's have a V-Block or a Lathe, pop down to your local Machine Mart they have loads of both and just ask if they wouldn't mind you testing your Laser...No purchase necessary .....

[John]

I think the V block method works well for the symetrical bodied collimators. You need to project over a decent distance though - 10 feet minimum. I aim to get the laser spot pretty much stationary on a spot around 15 feet distant as the colimator rotates around 360 degrees.

[Zakalwe]

My Revelation laser collimator was out when I purchased it. I used the Olly Penrice ©two-nails-whacked-into-a-lump-of-wood method to adjust it. Seems to have worked fine.

I can't see why the V-Blocks or the nails method would be out, unless, as others have said, the body of the collimator and nosepiece have their axis in the same plane (and as they screw together I can't see how they could be far out).

[Bizibilder]

Rather than nails you can make an exellent "V" block from four identical spheres (Roll-on deodorant bottles are a good source!). Just fix them (bit of glue) in a "square" formation on a flat surface, with all four spheres just touching both each other and the flat surface, You have a very good "V" block with two V's that are at precisely 90° to each other.

[knobby]

Mr pedantic here ... The sphere idea is only as accurate as the sphere manufacturers q.c. <img src='http://stargazerslounge.com/public/style_emoticons/<#EMO_DIR#>/tongue.gif' class='bbc_emoticon' alt='' />

Edit , actually disregard that , or would work , you're right !

[laser_jock99]

It's important to point out here that only the nosepiece part of the collimator (i.e. the bit that slides into the focusser) should be in the vee block. This is the only part of the collimator that needs to be co-linear with the beam. Remember the object of collimation is to line up the telescope mirror(s) with the optical axis of the focusser. Therefore the laser beam should- 1) be in the centre of the focusser tube & 2) be pointing exactly along it's axis. The datum surface is the inside of the scopes focus tube.

[Steve Ward]

To columnate mine I shimmed the end with one wrap of thin packing tape to get a nice fit ,

popped it into the EP holder of my ED80 Pro on the HEQ5 ,

swung the scope round to point at a convenient bit of wall 30' away and then rotated the laser in the EP holder ,

it projects the laser straight through the frac the same as fitting into the lathe , only we astronomer types are more likely to have a frac than a lathe . . .

Eliminates all that 'V' block faffing ........

Steve

[JamesM]

One of the advantages of the Hotech is that they come with a 2" adapter which can be secured into a similar size hole that has been cut into a vertically held piece of MDF. I have had reason to align mine which I did over a distance of about 15ft and haven't had a problem since. So likewise with your orion laser collimator, you could place it in one of Orion's eyepiece centering adaptors (which is a nice piece of kit to own anyway - details here) which is held in a similar size prepared hole that has been cut fairly tight but which has room to allow you to turn it around to test the position of the laser's beam against a wall etc.

James

[yeti monster]

Surely, a Cheshire or laser collimator is only for getting collimation close, once close a star test is the best way to perform fine tuning.

[John]

Surely, a Cheshire or laser collimator is only for getting collimation close, once close a star test is the best way to perform fine tuning.

Yes, that's how I see it. Final adjustments made using Polaris, usually

[Merlin66]

Please remember all these collimating "aids" are designed to "square up" the focuser to the optical axis.

If your eyepiece(s)/ camera nosepiece etc. don't sit VERY tightly into the focuser (which should NOT sag under load) then your eyepiece etc will still be mis-collimated to the scope's optical axis. This can make a hellva difference when using high powered eypeieces ( or small webcam sized CCD chips)

The final test should be a star test WITH THE EYEPIECE YOU WANT TO USE.

[steppenwolf]

I like laser collimators PROVIDED THEY ARE THEMSELVES PROPERLY COLLIMATED and that, for me, means doing it myself. I also use a Cheshire EP.

Nails are pretty crude although they do, of course work - a nicer method of checking the laser's collimation (with the caveats above about orthogonality of the housing) is to use some plumbing bits:-

[pat]

Thanks to you all for your input. It seems that I can't test my laser in a V block. The nosepiece is slightly smaller than the other end. In the Hotech pictures and article it has "why we should not test the laser alignment by putting it in a V block". My understanding is that the laser barrel has to be the same diameter when placed in the V block. Pat

[Skuber]

Pat,

I read that article from Hotech suggesting you can't use the V-Block approach because the contact surface should ONLY be the part of the collimator that goes into the eyepiece.

The problem with the Hotech is that the thin end that doesn't rest on the block is heavier than the thick end that goes on the block / in the eyepiece.

So, I was thinking, make up a simple V-Block for the thick end, then wrap a couple of elastic bands around it to keep the collimator on the v-block.

Then only the correct surface is touching the v-block and you should be able to check the collimation.

I haven't tried this yet, as my Hotech seems to be perfectly aligned, but this would be my approach if I needed to.

[Jason D]

Please remember all these collimating "aids" are designed to "square up" the focuser to the optical axis.

If your eyepiece(s)/ camera nosepiece etc. don't sit VERY tightly into the focuser (which should NOT sag under load) then your eyepiece etc will still be mis-collimated to the scope's optical axis. This can make a hellva difference when using high powered eypeieces ( or small webcam sized CCD chips)

The final test should be a star test WITH THE EYEPIECE YOU WANT TO USE.

You are referring to the tilt error between the eyepiece and the primary mirror focal planes which is not easily detectable/correctable by star collimation. Star collimation excels in detecting/correcting primary mirror axial alignment which can be corrected by primary mirror adjustments. The focal plane tilt you are referring to can only be corrected by secondary mirror adjustments which is difficult to accomplish by star collimation.

Jason

[Steve Ward]

I think the topic of conversation was the columnation of lasers not scopes ?

Steve.

[moriniboy]

Surely it would not matter if the scope end of the laser was 1.25" and the other end a bit bigger, it just means that when projected on the wall the laser dot would just be lower down.

As previouly mentioned the only foolproof way is to star test after the laser collimating has been carried out.

[pat]

This is also what I thought. Untill I read the Hotech article, looking as if to disprove this V block method. They refer to "none referencing point" When I started this project I wanted to compare the accuracy of my laser with that of a friend using the same laser and setup. Pat