Barlowed Laser Collimation Method

[ZOG]

I've been trawling the net looking for info on this as it seems to be the big thing in the states and they reckon you can get perfect collimation of the primary with it.

Anyhow I found a good tutorial about it here,

http://www.cameraconcepts.com/barlowed%20laser%20collimation.pdf

Seems easy enough to make and with those of us with F5 or faster scopes could be just what we need.

[mike-h]

An excellent find. Newcomers who havent seen this before will find it a great help.

Mike-H

[calibos]

Well its a way of getting Cheshire quality collimation with a Laser, which for most people is enough. It doesn't enable 100% perfect collimation. One still needs an auto collimator for that.

Assuming the laser is collimated perfectly itself then an unbarlowed laser can be as good as most other methods to adjust the tilt of the secondary. However due to slop in focusers etc one can't really rely on an unbarlowed laser to give cheshire level collimation of the primary. The barlow method gives a laser this cheshire level accuracy.

What this means is that one can put away the cheshire and the torch and if one has a truss, even do away with all the backwards and forwards adjusting the primary and checking back at the focuser, because one can see the donut shadow one needs to centre reflected in the secondary mirror from the back of the scope at the primary collimation knobs.

The only thing I used my cheshire for was to help collimate my laser when it went out of wack. ie. instead of messing about with V-Blocks and targets on walls to collimate the laser, I'd collimate the scope perfectly with the cheshire in daylight, insert the laser and then adjust the lasers collimation screws to centre the laser dot in the donut (Remember the scope is already collimated perfectly with the cheshire, if after inserting the laser, the dot doesn't land in the middle of the donut then we know its the laser thats out of collimation, not the scope. Collimating the laser to the already collimated scope is much easier I find than messing about with the V-blocks and targets like I said)

[irishbloke]

I had a go at this and found it pretty good. Just finding the right way to cover the end of my focusing tube as the barlow isnt visble from the end and has know thread for a filter. The airy discs or whatever did look much better as I adjusted the secondary to the right position with the vanes and a colli cap. was scared to mess with vanes before so had just left them as was which had a bit of primary missing.

I've drilled a hole in a cap that fits into the tube just right. It's just finding a way to hold it there.

Anyway thanks for this.

Brian

[yeti monster]

[novice mode=on] the article doesn't cover removal of the "doughnut" from the primary mirror, would this;

a, disturb the position of the primary?

b, leave an adhesive reidue, the cleaning of may result in a, (above)

[/novice mode firmly remaining in the on position]

[ZOG]

That's because you don't remove it, you're looking for the reflection of the doughnut at the barlow lens.

[yeti monster]

I meant after collimation is completed.

[ZOG]

I cant comment on your scope but mine came with a donut marking the centre of the primary. In any event, it could be left in place without affecting the mirrors performance.

[daz]

Yes, leave the donut in place, it will not affect the views in anyway.

Of course, if your donut is not central, that's another issue :)

[daz]

The only thing I used my cheshire for was to help collimate my laser when it went out of wack. ie. instead of messing about with V-Blocks and targets on walls to collimate the laser, I'd collimate the scope perfectly with the cheshire in daylight, insert the laser and then adjust the lasers collimation screws to centre the laser dot in the donut (Remember the scope is already collimated perfectly with the cheshire, if after inserting the laser, the dot doesn't land in the middle of the donut then we know its the laser thats out of collimation, not the scope. Collimating the laser to the already collimated scope is much easier I find than messing about with the V-blocks and targets like I said)

What a flippin good idea!!

[Merlin66]

Guys,

help me here....

I understand this can give excellent collimation etc BUT if the focuser can't hold an eyepiece and or a CCD camera square and central to the light beam, the end result on the image will still show an out of collimation problem??????

[calibos]

What a flippin good idea!!

I should have mentioned, one has to make sure to position the laser the same way in the focuser every time.

The V-Block method done right will collimate the laser perfectly but I just found it a chore. To get the best accuracy you want as large a distance as possible between the laser in the block and the target on the wall but as a corrolory to that, the slightest movement of your V-Block clamped to the table screws everything up and you have to start again. Also, a lot of lasers have bevels or sticky outey bits that tilt the laser in the V-Block as you rotate it.

Like I said I just found it frustrating and a chore.

With the Cheshire/Scope Laser collimator collimation idea one can't collimate the laser 100% perfectly for any position of the laser, one can only collimate it to one position. But thats fine, one just makes sure one always inserts it in the focuser the same way each time. With my old Orion Lasermate delux, one always wanted the 45º face facing the back of the scope anyway. So I just found a letter on the label that lined up with a particular drawtube screw and always aligned it exactly to this screw.

Speaking of the Orion Lasermate Delux. Its unique in that it has a white bullseye target on the 45º face. One can 2x barlow it and with a solid tube dob not have to mess around with barlow targets or running back and forth from the primary collimation bolts to the front of the scope to look up the drawtube at the target.

Because the donut shadow goes back through the barlow without a barlow target it is much larger and more diffuse and fainter than the standard barlow method. Not a problem with the lasermate delux though because the white target makes this diffuse donut shadow still visible and the rings of the white target help one to centre this large shadow ring. On any other laser with the plain metal 45º face its not bright enough and its impossible to centre this much larger than normal shadow around the laser hole.

So the Orion is great for Solid tubes. With a truss though where one can see the reflection of the barlow target up the drawtube in the secondary mirror from the back of the scope, its probably better to go with the traditional barlow method with its much more distinct donut shadow.

Heres a pic of the shadow on my Howie Glatter Laser barlow target.

[irishbloke]

I love this method. I didn't have a barlow with a filter thread to attach a filter with a white card and a hole in the centre, so I had to dismantle a cheapy balow put a red filter and donut white card on front attached to the holder.

I then inserted my tal x3 barlow and baader lazer into this.

It' works okay but I have to use a mirror to see up into the focuser tube.

I decided it might be easier to place a cap over the focuser tube. I have drilled a hole in the centre of a cap and wrapped some plastic round it to centre it.

This means I can easily see it from the top of the tube without putting anything else in the tube.

I want to make a better focuser tube cap as the other was a bit lame.

Inspite of all this I think this is a great method and can see how it will be dead easy at night.

Thanks again.

Brian

[irishbloke]

I love this method. I didn't have a barlow with a filter thread to attach a filter with a white card and a hole in the centre, so I had to dismantle a cheapy balow put a red filter and donut white card on front attached to the holder.

I then inserted my tal x3 barlow and baader lazer into this.

It' works okay but I have to use a mirror to see up into the focuser tube.

I decided it might be easier to place a cap over the focuser tube. I have drilled a hole in the centre of a cap and wrapped some plastic round it to centre it.

This means I can easily see it from the top of the tube without putting anything else in the tube.

I want to make a better focuser tube cap as the other was a bit lame.

Inspite of all this I think this is a great method and can see how it will be dead easy at night.

Thanks again.

Brian

[Andrew*]

I just tried this method for the first time the other day. I did have the problem that I couldn't see inside the focuser tube, but otherwise I had a pleasure of a time and got very accurate collimation, confirmed by the cheshire.

Full collimation of both mirrors took less than 15 minutes from start to finish, and I was totally out of practice too! But a bright laser is essential for daylight collimation, because the beam can be very faint coming back.

Thanks for the link!

Andrew

[Talyn]

I meant after collimation is completed.

It stays in place all the time. You'll need it next time you collimate your scope and you don't want to be messing around putting a paper ring on your mirror all the time. The ring, as someone says above doesn't affect the view or light gathering capabilities of the mirror in any way. This is because the centre of the mirror is in the 'shadow' of the secondary.

[earth titan]

Looks like a winner.

Tried to collimate the 12" with a laser, with limited success as it needs aligning.

Cheshire is more accurate but a pain with trying to alter the collimation and continually looking back at the cheshire.

Anyone know if the laser has to 'true' (collimated) and lined up for it to work properly as the one which came with the scope is a major piece of imprecision engineering although it can be adjusted (I think)?

[Tim]

The laser output is made parallel by the barlow, so even if it isn't brilliantly collimated (few are) then it should be ok.

There is still the problem of focusser slop of course, or just a poorly fitted laser which wiggles around, which is why the Hotech lasers with self centring fitting are so good, well worth the money.

[ZOG]

When you put the barlowed laser in the focuser you will see a patch of red light on the primary rather than the usual dot. If this patch covers your centre spot then you should see it's shadow on the target. If so, collimation will be good no matter how much slop you have.

[earth titan]

This should be a super sticky!

Just tried it with my Lightbridge....

This is the best tip I have ever been given....!!

Accurate collimation, in the dark, in 5 minutes.

Going to make a more permanant end cap for the barlow, now I know it works. Call me happy

[angusb1]

Guys,

help me here....

I understand this can give excellent collimation etc BUT if the focuser can't hold an eyepiece and or a CCD camera square and central to the light beam, the end result on the image will still show an out of collimation problem??????

This is true in my experience. My old focuser had quite a bit of movement in it and when I had collimated the scope with it in a certain position it would go straight out as soon as the focuser moved again.

[russ]

Well worth picking up one of the Orion/Antares self centering 2"-1.25" adapters. They hold the 1.25" eyepiece/laser in the same place everytime. It all works out a lot cheaper than the Hotech.

Orion Precision Centering Adapter - SCS Astro

[Keiran]

Sounds like a good idea im going to have a go thanks

[earth titan]

As I undertsand it (and I tried this last night to see) focuser slop, laser alignment etc are unimportant.

The technique relies on reflecting light from the primary and using the paper cover on the botom of the Barlow as the target rather than the standard collimated laser light. I rotated and wiggled the focuser, laser etc. to see if the the reflection of the centre spot moved but nope.

It really doesn't make sense until you have a go (like most things). Found I needed a small mirror to see up into the focuser but no big drama or expense.

I was interested to see how it was going to work myself with a laser collimater which doesn't give a 'dot' but a smudge and isn't well aligned. Took it apart to see if I could improve it, made a few adjustments but in the end, Meades laser collimater is just a cheap novelty laser pointer in a holder.

I checked the collimation with my cheshire afterwards and it was spot on.

All with a piece of card with a hole in and some gaffer tape!!

[Jason D]

Keep in mind that barlowed laser only corrects the primary mirror alignment. It does not correct the secondary mirror alignment. That makes barlowed laser similar to the cheshire (not the combo tool), to the collimation cap, and to star collimation. None of these tools correct the alignment of the secondary mirror.

For the record, barlowed laser method was invented by Nils Olof Carlin.