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Barlowed Laser Collimation Method

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From experience, I have had a laser reading perfect collimation, when in actual fact the secondary was far from square to the focusser. Rotating the secondary into position and keeping it there while you tighten it and getting it perfect is the hardest part for me :s

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I've never touched my secondary mirror, As the fist scope I had I moved it and was buggered and could never sort it again lol, But I always use the barlow and laser, my laser is well out and scribes big circles when rotated and still works fine (with the barlow)..

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From experience, I have had a laser reading perfect collimation, when in actual fact the secondary was far from square to the focusser. Rotating the secondary into position and keeping it there while you tighten it and getting it perfect is the hardest part for me :s

You might want to try the idea of inserting plastic washers cut from a milk container as shown in the attachment. This is a great idea to fine tweak your secondary mirror. I use two plastic washers. I came up with this idea sometime ago and many have tried it since with positive results. The soft plastic washers allows you to tweak one set screw to make fine adjustments without the need to touch the other two screws. The elasticity of the plastic work like micro-springs.

post-17988-133877490146_thumb.png

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I've never touched my secondary mirror, As the fist scope I had I moved it and was buggered and could never sort it again lol, But I always use the barlow and laser, my laser is well out and scribes big circles when rotated and still works fine (with the barlow)..

Your primary mirror focal plane must be at an angle with respect to the eyepiece focal plane. This is more of a problem for imaging compared to visual observing.

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Thats a good idea Jason, I think i'll give that a go if my GSO ever comes out of hibernation.

But what about the rotation of the secondary within the tube, is there a better way of getting that right, other than by eye? Thats what I struggle with.

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for what its worth...ive found a great way to collimate a laser is to stick it in a lathe ad rotate it off the fathest wall .......a friend of mine has one...i appreciate not everyone has access to one

ive now got one of the high end Kendrick lasers 2" barlowed type.....and that is spot on, they have a purpose made diode which is set in a machined block (which you can see in the link) and has a tiny spot size..... They are collimated at the factory.....quite expensive but really superb.

KAI - Lasers

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But what about the rotation of the secondary within the tube, is there a better way of getting that right, other than by eye? Thats what I struggle with.

I am afraid using a quality sight-tube and your eye is the best way to go.

Here is a hint: Always check the secondary mirror dark reflection at the center of your view. It needs to be circular and shifted towards the primary mirror. I am not saying align your secondary mirror by observing the dark reflection but rather use the secondary mirror dark reflection to evaluate your final alignment . Check the attached animation. See how the mirror dark reflection tracks the secondary mirror.

Jason

post-17988-133877490454_thumb.gif

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That's a useful animation Jason, nice one! :(

Could you please elaborate on the phrase "shifted towards the primary", do you mean the centre of the primary as indicated by the donut/catseye triangle?

Cheers

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That's a useful animation Jason, nice one! :(

Could you please elaborate on the phrase "shifted towards the primary", do you mean the centre of the primary as indicated by the donut/catseye triangle?

Cheers

See attachment.

Left diagram represents a good collimated scope. Note how the secondary mirror shadow is circular and shifted to the right hand side (towards the primary mirror). The secondary mirror shadow is shifted even though the secondary mirror looks centered and circular under the focuser.

Right diagram represents a scope with a secondary mirror that can benefit from some improvement. Note how both the secondary mirror appearance under the focuser and its shadow looks elliptical and pointing away from the primary center.

The point of my last post is that scope owners can also evaluate the secondary mirror shadow to assess the alignment of their secondary mirror.

Jason

post-17988-133877491029_thumb.png

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With the Barlowed Laser method, dose the laser collimator have to be that well collimated its self?

I ask because if you can wobble it in the focuser and the reflection dose not move, that suggests that if the collimator is out, it will not matter as long as it is always in the same position in the focuser?

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The laser accuracy for barlowed laser is NOT stringent. However, the whole center spot has to be covered by the diffused laser.

Bear in mind that barlowed laser is only used to align the primary mirror. You also need to alignment the secondary.

Jason

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Hi Jason,

I am not sure I would ever align the secondary with a laser collimator anyway; I find it can be misleading. I prefer a sight tube for the secondary.

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A sight tube is good for adjusting the rotational and lateral alignment of the secondary. A well collimated laser is good for adjusting secondary tilt, assuming a centre marked primary.

I use the barlowed laser method for my primary - it's very accurate I find.

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I have a centrally marked primary, so I will give the laser method a go for the secondary tilt.

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i wouldnt do that. id be worried about what it could to to the catalytic converter and o2 sensors. plus methanol is corrosive. it will corrode your fuel lines and it leaves a layer of white corrosive dust on cylinder walls after the car has been turned off as well as clogs fuel injectors.

Have you got your forums muddled by any chance?

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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.

I'm even more confused than I was to start with..... what do you adjust? Grub screws or tensioners. Why do you have to keep re-allining and why doesn't the product come with these if they are so nessecary?

I suppose that if I had a scope it might help a bit more...........

Edited by stardad
added last line

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Another method with alot less mucking about is a self alignment compression ring like the one sold by orion optics, it wont take the focusser travel slop away, but the insertion slop should improve ( ive yet to get one ) ive found the barlowed spot too large and diffuse to accurately centre inside the primary sticker though as mentioned its the primary alignement that the barlowed laser is getting at, then just use a glow in the dark colli cap to align the primary to the focuser. if the spot is bang in the middle that has to be fairly in tolerance i think, Only problem is the glow in the dark paint on the inside of the colli cap wears out, but can be reaplied by a touch up with some glow in the dark paint purchased online ( need to do that myself ) as i get about 30 seconds of illumination now, where before i had about a min, min and a half of glow time. I can get the laser fairly smack in the middle of the primary sticker, the secondary aligned under the focuser correct. the primary aligned with the focusser, using these methods. the only error i havent figured out, is the primary inside the secondary is often never perfectly centred and is mostly slightly off. not sure if that error is the spider vains needing adjusting, but i suspect it is, the images i get though have been fairly consistent so ive left the spider vains alone to reduce the primary not exactly centred inside the secondary problem, if anyon can confirm thats likely the culprit that could do with tweaking ? i have a fairly healthy amount of free space around the primary inside the secondary, so i dont belive that error is night and day type error, only those with as small a secondary as is possible with say a 1 or 2 mm clearance of the primary inside the secondary do i belive this error would be crucial, though of course could still be improved slightly none the less if the primary isnt exactly centred inside the secondarys edges

Edited by neil phillips

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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)

Thats assuming your focusser is square and spider is properly aligned though surely ? if either is slightly out you would inaffect be putting your laser out, by assuming the scope was perfectly collimated, as the spider error or focusser error could be taken up when adjusting with the cheshire could it not ?

Edited by neil phillips

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Thats assuming your focusser is square and spider is properly aligned though surely ? if either is slightly out you would inaffect be putting your laser out, by assuming the scope was perfectly collimated, as the spider error or focusser error could be taken up when adjusting with the cheshire could it not ?

Bear in mind that the laser beam uses very small area of the secondary mirror surface. It does not use or reference the secodary mirror edge. Therefore, whether the secondary mirror is perfectly positioned under the focuser or not will not make a difference for the laser.

Jason

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Ok i wasnt sure, so was just discussing this idea, so what collimation errors could throw off the idea of perfectly collimating a scope to check laser accuracy then ? just seems like theres too many variables to be certain, as much as say turning the laser in a vice, it would worry me collimating a laser as suggested by collimating the telescope

Edited by neil phillips

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V-block testing/adjusting will improve the collimator but will not perfect it. Even if the V-block test passes, there are other issues with a mass produced laser collimator which include the size of the laser beam and how well does it seat in the focuser.

The way I adjusted my mass produced laser collimator is by adjusting it in my scope after I had I collimated it with my Catseye collimation tools. Interestingly, my laser now gives good results but only when it is inserted in the same orientation. It gives different results when I rotate it by 180 degrees.

Jason

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I am starting to think from a lot of comments that lasers straight from the manufactorer are rarely aligned well enough, i wonder what percentage of lasers are actually in tolerance straight from the manufactorer ? the error im getting is i can have all the angles looking pretty well spot on using a colli cap for the secondary and either cheshire for the primary or glow in the dark colli cap for the primary, as soon as i centre the laser in the primary sticker, ( its always off by about 5mm ) the secondary goes off, with the veiw of the primary inside the secondary now slightly too far right. Which leads me to suspect assuming my spider vains are centred, that the laser is indeed off. so what should i trust the laser, or the veiw of the primary looking central in side the secondary ? im guessing the visual veiw should be trusted. If this is indeed a accurate way to align the laser, maybe i should get the visual view spot on then adjust the laser so when its centred in the primary sticker, i do not get the error mentioned of the primary looking to far right, inside the secondary reflection, assuming theres nothing else producing this error when the laser is centred ( as i asked earlier could the spider be producing this error ) and the laser isnt actually out ? untill i know the answer to that, im not sure if i should trust my visual collimation or the lasers collimation. so basically if the visual veiw is good, but the laser is off. then it is indeed safe to collimate the laser to the visual view.

Edited by neil phillips

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untill i know the answer to that, im not sure if i should trust my visual collimation or the lasers collimation.

Neither. Both are susceptible to errors. The laser could be off or/and your eye axis could be off with respect to the focuser axis (refer to attachment). It is hard to tell.

Also check the following recent thread with a similar issue.

http://stargazerslounge.com/equipment-help/131772-collimation-process-still-not-quite-right.html

Jason

post-17988-13387753774_thumb.jpg

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I know what you mean, problem is if one cant trust either its hard to perfect it any better. I have the baarder laser with no way off checking its collimation, so what to do with that scenario ? i can get it looking fairly good under the focuser, with paper blocking the primary relection up down left and right is fairly even, not perfect but close, If i collimate visually, and get the primary looking evenly centred inside the secondary ( i cant use the clips as they are to far in to tell ) the dark shadow around the primary inside the secondary looks elliptical, so i centre that so all sides look even, Ive noticed on the diagrams, the shadow looks more circular around the primary inside the secondary. So im unsure why the dark shadow looks elliptical,is this a problem or just a illusion ? if its centred as best i can do, even though it looks elliptical will this be close ? with the visual collimation described the laser is on the edge of the primary sticker, as soon as i centre the laser, the elliptical shadow around the primary inside the secondary goes off, ( it goes slightly right and often up a bit ) but without knowing if the laser is collimated it could infact be close to the centre primary sticker, i have no way off knowing ? if i assume the laser is collimated and centre the beam inside the primary centre sticker, the error of the shadow around the primary inside the secondary. is indicating something is slightly off, assuming the laser is collimated, could this final adjustmemt be the spider ?

Edited by neil phillips

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Will it be possible to take a photo from your focuser and post it?

I am attaching two photos taken from my focuser for reference.

post-17988-133877538391_thumb.jpg

post-17988-133877538396_thumb.jpg

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