AstroSystems Laser Collimator with Barlow arrived...problems

[Tannehill]

Well, that fuzzy edge seems intermittent and moving about, now. Perhaps that was due to slight off-centering of the camera lens in the focuser tube....

Now the main issue is that your chesire and laser technique don’t agree, right?

You say the laser mark is off after collimating with the chesire….a cm or so…Can you describe your steps exactly in order?

The primary or first-out laser beam of the collimator, and the chesire, assess different things. The former for secondary adjustment, the latter for primary mirror adjustment. One can be on while the other is off, actually. However, the return-beam adjustment and the chesire should agree….assuming your laser is collimated, that is.

If the laser is not collimated, that return beam method won't work right. That's the vulnerability of laser collimators. If the laser beam isn’t drilling right down – and co-incident with – the central axis of the focuser (which should be the same as the central axis of the collimator chasis) – then it’s cactus. An un-collimated laser collimator is good for lecturing and exercising cats…and that’s about all. Unless you have a barlow attachment, in which case it'll still work for primary collimation...but that isn't relevant in your case....

When in doubt here about your primary mirror’s collimation, of all the tools you have as you describe, believe your Chesire.

You likely don't have a V-block for testing your laser's collimation, but a second-best method is to put the laser into the focuser tube, and, with the set screw loosened obviously, spin the collimator in the focuser and watch the beam on the mirror. If it describes a circle on the mirror as you spin the collimator, your laser is not collimated and you should either return it or collimate it if you can.

But, I’m pretty sure that correctly centering your secondary mirror under the drawtube (adjusting the center screw) will not correct the problem you describe: that the chesire and your laser merge-the return-beam-method do not agree. Centering the secondary under the focuser is still valuable, but will not fix this part.

Secondary position - under the focuser correctly or up or down or over a bit - is not really a "collimation" issue, but rather a way to avoid missing some of the light cone (vignetting). Assuming of course that you have already dialed in the secondary’s collimation (that is, it’s “tilt”) using a collimated laser, adjusting the screws so the laser beam hits the primary mirror center mark. That IS a true collimation issue. We can (and many will) argue about the practical definition of collimation, but IF a flat diagonal mirror's "tilt" is correctly reflecting the center of the focuser axis to the center of the primary mirror, but is "shifted" a bit to miss some of the light, your star test will still be correct, but your image will be less bright, so a purist could argue this isn't a collimation issue but rather vignetting.

The next step is checking your laser’s collimation. The other (less likely) explanation is that the collimator is not sitting flush straight in the drawtube and when you tighten the set screw, it tilts off-axis….but that’s unlikely, unless there is some flawed lip on the collimator’s rim….

My two cents...

Cheers,

Scott

[DJVege]

Hi Scott,

Much appreciated!

I'm fairly sure the laser collimator is collimated as that is the whole point of getting this particular collimator. You aren't advised to ever collimate the laser yourself. It's supposed to keep it's collimation...if not, send it back and they'll recollimate it for you. However, I'll test this with the drawtube method when I get back home tonight. This laser collimator has a barlow attachment as well.

I'll test the laser's collimation and report back here tonight. Thanks a lot for your explanations and suggestions.

[matt]

DJ.

Those laser collimators can go quite easily out of collimation themselves.

When I used to have a newt I purchased a laser collimator and tested it 'out of the box' and it was a mile out.

It was one of these: http://myastroshop.com.au/products/d...asp?id=MAS-143

Although I purchased the unit from somewhere else, I think.

You can collimate it yourself. There are 3 little hex screws which are used for this purpose not too far from the grub screw which turns the laser light on and off.

You can make a simple tester from a block of wood and some screws.

By placing the colliamator horizontally in the tester, projecting the beam onto a distant wall and rotating the unit, you can tell whether your unit is out of collimation. If the dot on the wall stays in the same point while rotating...you are fine. Otherwise you need to adjust those screws until it doesn't form a looping sort of arc as you rotate the unit.

I'll try and find a link to the DIY tester for you.

[Omaroo (Chris Malikoff)]

DJ - test it easily yourself by laying it on a glass surface and turning the laser on. Draw a line on a piece of paper and aim the laser at that line. Roll the device along the table and see it it maintains the same dot height relative to the line or not.

Also, mount the laser in your focuser and nip the clamp up lightly so you can rotate the laser. If you rotate it, does the beam move relative to the primary's dot?

Although these are meant to be non-adjustable in day to day circumstances, a decent enough hit will knock it out of whack like any other. It isn't impervious to de-collimation, just more resistant than most.

[matt]

Originally Posted by Omaroo

Also, mount the laser in your focuser and nip the clamp up lightly so you can rotate the laser. If you rotate it, does the beam move relative to the primary's dot?

Chris.

This can also be a sign of poor machining in the focuser.

[Omaroo (Chris Malikoff)]

Matt - this is nothing like the typical laser collimator. Sorry to point this out, but everyone is assuming that it is. Go here to see that it is completely different:
http://www.astrosystems.biz/laser.htm

Originally Posted by matt

DJ.

Those laser collimators can go quite easily out of collimation themselves.

When I used to have a newt I purchased a laser collimator and tested it 'out of the box' and it was a mile out.

It was one of these: http://myastroshop.com.au/products/d...asp?id=MAS-143

Although I purchased the unit from somewhere else, I think.

You can collimate it yourself. There are 3 little hex screws which are used for this purpose not too far from the grub screw which turns the laser light on and off.

You can make a simple tester from a block of wood and some screws.

By placing the colliamator horizontally in the tester, projecting the beam onto a distant wall and rotating the unit, you can tell whether your unit is out of collimation. If the dot on the wall stays in the same point while rotating...you are fine. Otherwise you need to adjust those screws until it doesn't form a looping sort of arc as you rotate the unit.

I'll try and find a link to the DIY tester for you.

[matt]

Don't be sorry, mate. You've done nothing wrong.

My mistake. Came in on the discussion late and assumed we were talking about the more common laser unit.

However, is it still required to be inserted in a focuser?

[DJVege]

Yep. Thanks guys. Here's hoping the laser collimator is off. Then we'll have found the culprit, and it means my collimating techniques are wrong with the cheshire! LoL.

Omaroo..what do you mean nip the clamp up tightly so that I can rotate the laser? Which clamp? What am I rotating? I thought I just put the collimator in, don't screw in the collimator to the 2" tube...and simply turn the whole laser collimator in the tube. Not right?

Which screws/clamps on the laser collimator can I play with?

[DJVege]

Originally Posted by matt

Don't be sorry, mate. You've done nothing wrong.

My mistake. Came in on the discussion late and assumed we were talking about the more common laser unit.

However, is it still required to be inserted in a focuser?

You're right, Matt. Which is why I will perform both tests. Roll on floor, and twist in focuser.

[Omaroo (Chris Malikoff)]

LOL! No probs Matt. It's just that last time this unit was discussed someone refused to believe that it wasn't constructed the same as the type you've pointed out and added their argument based on that assumption. This unit, although technically able to be collimated, (set screws are glued in place) comes with a free "return to manufacturer" clause if it needs re-collimation. You are only up for postage - they do't charge anything for the service. Of course, if you want to break the warranty you could chip the glue away and collimate it if your really wanted to.

Originally Posted by matt

Don't be sorry, mate. You've done nothing wrong.

My mistake. Came in on the discussion late and assumed we were talking about the more common laser unit.

As you were.

However, is it still required to be inserted in a focuser?

[Omaroo (Chris Malikoff)]

DJ - just insert the 2" collimator into the 2" focuser as per normal. GENTLY tighten the ring clamp on the focuser - barely tight enough to hold the collimator so that there's no obvious slop but so you can grab the collimator and twist it while it's sitting there. If you twist the collimator and the dot moves in a circle on the secondary then the beam isn't straight. So - in essence - do step 1 (adjust the secondary to get the dot in the primary's circle) and then twist the collimator gently. If the dot moves, let's discuss it at that point.

You've got a wee complex problem here because a) you have a MakNewt and b) you've replaced the focuser with a non-standard one. These two will add an extra dimension of variables for us to figure out.

Originally Posted by DJVege

Yep. Thanks guys. Here's hoping the laser collimator is off. Then we'll have found the culprit, and it means my collimating techniques are wrong with the cheshire! LoL.

Omaroo..what do you mean nip the clamp up tightly so that I can rotate the laser? Which clamp? What am I rotating? I thought I just put the collimator in, don't screw in the collimator to the 2" tube...and simply turn the whole laser collimator in the tube. Not right?

Which screws/clamps on the laser collimator can I play with?

[matt]

Chris......isn't there still room for machining error to enter into the equation if you are rotating the collimation unit inside the focuser?

We're assuming all contacting surfaces are perfectly machined and the unit is perfectly centred.

[Tannehill]

Ah, you do have a barlow attachment, then.

Use that to adjust the primary mirror, not the return beam-only method. Get the shadow of the primary center mark centered around the hole in the back of the barlow attachment. In "barlow" mode, mis-collimation of the laser won't matter. Then, see if that agrees with the Chesire.

Then compare the agreement using the primary laser to align the secondary and the return-beam method to align the primary.

If the former method agrees, but the latter disagrees (as you say it does now) then I'll bet you it's the laser's collimation as the issue...

S

[Omaroo (Chris Malikoff)]

Originally Posted by matt

Chris......isn't there still room for machining error to enter into the equation if you are rotating the collimation unit inside the focuser?

We're assuming all contacting surfaces are perfectly machined and the unit is perfectly centred.

Absolutely Matt - it's only a rough indicator - but one that will work nontheless.

[DJVege]

Tannehill,

I've done that, and the barlowed laser doesn't agree with the cheshire. It's the same, about a cm off. But just to be sure, I'll perform this test as well tonight.

Thanks guys.

[matt]

Originally Posted by Omaroo

Absolutely Matt - it's only a rough indicator - but one that will work nontheless.

I'd want to eliminate the machining of the focuser and the laser unit itself as factors before blaming the collimation of the laser.

But all things being equal...it's most likely the laser unit is out of collimation.

[DJVege]

haha. Well, place your bets gentlemen! Around midnight tonight, I shall post my results!

[Tannehill]

well, heck, I dunno then...

Hmm, well, if the telly has poor offerings I'll check in here then for the suspense-filled outcome...

s

[Omaroo (Chris Malikoff)]

Same here LOL! If the sky is CRYSTAL clear, I may be up.

Otherwise...sleepybyes....

[matt]

Originally Posted by Tannehill

well, heck, I dunno then...

Hmm, well, if the telly has poor offerings I'll check in here then for the suspense-filled outcome...

s

You really are short of excitement around your place.