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dnl

Collmination cap or laser

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Hi Ive just bought a xt10i which compared to my previous little scope is a bit faster and understand collmination is more important .

I thought i had it sussed with a laser tool which ive checked buy rolling on its side in the kitchen and checking it against a dot on the wall about 10m away.

But this scope came with a collmination cap so thought ill try that i should know how to do it for future reference.

All  straight forward line everything up seemed very easy.

Until i put my laser back in and found the laser dot was about 1.5" away from my primary mirror centre mark.

Ive had a google watched the youtube videos and cant think what im doing wrong should i ditch one and never go back? or is it trial and error and see what happens when i finally get a clear night.

Any help would be appreciated

 

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When you check that the laser collimator is itself collimated, 10m is a good distance and the laser unit needs to be rotated just around it's long axis with no other motion. A simple "V block" can help with this. Something like this will do the job:

https://www.thingiverse.com/make:334814

Assuming that the laser is now collimated accurately itself, if the laser spot is missing the central mark on the primary this means that the tilt of the secondary mirror needs to be adjusted. Once you have done that and the laser spot is right in the centre of the primary mirror, you then move on to see if the returning laser is striking the centre of the 90 degree target built into the laser collimator. If it is not then primary tilt adjustments are needed to get it central. It's important to do the secondary tilt first followed by the primary tilt.

Then star test when you get a clear night.

Edit: trying to get different collimating tools to agree with each other can be a thankless task !. I tend to stick with the method that results in an accurate star test and stay with that. For me that has been a cheshire eyepiece but a laser collimator can do a good job if properly collimated and if the correct order of steps is followed.

 


 

 

 

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I totally agree with the above. Check the laser is collimated.

I made a V block and rested the laser on that and pointed it at a piece of paper blu-tacked marked with a X to a wall and gently rotated the laser. It was quite a way out. But you can dig out the sealant on the holes covering the collimating screws and adjust.

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Thankyou John

Ill wait for clear skys and see which works

Dave

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14 minutes ago, baggywrinkle said:

I totally agree with the above. Check the laser is collimated.

I made a V block and rested the laser on that and pointed it at a piece of paper blu-tacked marked with a X to a wall and gently rotated the laser. It was quite a way out. But you can dig out the sealant on the holes covering the collimating screws and adjust.

I had the same issue when i bought the laser it makes you question your technique when you have to collimate your collminator.

Dave

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I shake my head in wonder that people can get away with selling something, often expensive, that simply doesn't do the only thing it's supposed to, and be not designed to be adjusted by the user without e.g. digging out sealant. I'm not sure who I blame more, the manufacturer or the retailer if it's a specialist retailer. With collimating lasers it seems you'd be sending back items time after time after time: perhaps those retailers themselves should ensure they're collimated before they go out. In similar vein I've had to throw away useless spirit levels that were more than a degree out...

rant over

M

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Captain magenta I totally agree my first laser would not collimate what so ever tried for days just would not stay anywhere near Central ended up chucking it in bin not before fine the 3 grub screws were all different lengths.

Bought a second that was out but that was easy collimate.

Like you said they should be tested before they put the silicone in the holes by the manufacturer.

 

 

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The only method I use with a laser is when it is Barlowed. Colli cap, specifically Blackcat XL, is more than sufficient for secondary collimation. I haven't found a laser out the box yet that 'does what it says on the tin'

Al 

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Had two Hotech lasers and both were perfectly colimated out of the box Tried a few others but none were close to being colimated.. Lasers though do require a decent focuser to work properly. For secondary collimatiion nothing beats a Concentre for accuracy but  they are a bit pricy..

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14 minutes ago, Ally8446 said:

... I haven't found a laser out the box yet that 'does what it says on the tin'

Al 

Glatter laser, but you have to swallow hard before paying up. I was lucky enough to find the once-in-decade 2nd hand one a few months ago... And another vote for the Concenter too

Edited by Captain Magenta
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just going back to the OP, difference between Coll cap and Laser, it could be that the focuser tube is out of alignment, ie not square / lined up to the main tube.  This doesn't normally show itself on a coll cap, but a laser will pick it up.  Checking that is a little more difficult; you need to find the diametrically opposite point of the focuser center inside the main tube, and then make sure a collimated laser points directly at it...

HTH

Mike

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17 minutes ago, johninderby said:

Had two Hotech lasers and both were perfectly colimated out of the box Tried a few others but none were close to being colimated.. 

I’ve had a Hotech for a while, again, perfectly collimated out of the box and I love the compression ring that centres it perfectly in the focuser, no tightening thumb screws that can send it off centre. They are expensive but if you have a Newtonian especially, they are a good investment and worth the extra cost

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A good point. Unless you have a properly set up focuser a laser may not give very acurate results. Also if the focuser drawtube shifts as it moves more problems.

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2 hours ago, Captain Magenta said:

I shake my head in wonder that people can get away with selling something, often expensive, that simply doesn't do the only thing it's supposed to, and be not designed to be adjusted by the user without e.g. digging out sealant. I'm not sure who I blame more, the manufacturer or the retailer if it's a specialist retailer. With collimating lasers it seems you'd be sending back items time after time after time: perhaps those retailers themselves should ensure they're collimated before they go out. In similar vein I've had to throw away useless spirit levels that were more than a degree out...

rant over

M

Actually, I got a cheap laser collimator as soon as I heard it was possible to collimate it by yourself. 

Initially, I was skeptical towards those as it seems that a bad laser collimator would mess up collimation more than it would improve it but knowing I could easily fix it I got one on eBay for £15. It was totally off when it arrived but I managed to fix it easily and I now get quick half decent collimation. Before that I "used" a cheshire but could not understand how it was supposed to be working so I didn't collimate at all (let the one who has never been axious about collimation throw the first stone)

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15 minutes ago, Raph-in-the-sky said:

. Before that I "used" a cheshire but could not understand how it was supposed to be working 

Yeh, Cheshire’s have always been a bit of a mystery to me too 😀

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44 minutes ago, mikeyj1 said:

just going back to the OP, difference between Coll cap and Laser, it could be that the focuser tube is out of alignment, ie not square / lined up to the main tube.  This doesn't normally show itself on a coll cap, but a laser will pick it up.  Checking that is a little more difficult; you need to find the diametrically opposite point of the focuser center inside the main tube, and then make sure a collimated laser points directly at it...

HTH

Mike

Would taking a measure from the top of the tube to the point the laser hits on the bottom of the focuser and on the far side of the tube then make sure its at the furthest point from the centre of focuser (piece of string) give me a good enough alignment ?

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1 hour ago, mikeyj1 said:

just going back to the OP, difference between Coll cap and Laser, it could be that the focuser tube is out of alignment, ie not square / lined up to the main tube.  This doesn't normally show itself on a coll cap, but a laser will pick it up.  Checking that is a little more difficult; you need to find the diametrically opposite point of the focuser center inside the main tube, and then make sure a collimated laser points directly at it...

HTH

Mike

Thankyou Mike

Bang on.

Just pulled my spider out and luckily the holes line up with the focuser so finding the diametrically opposite point wasnt to hard.

Adjusted the focuser colmination a bit.

Refitted the spider making sure it was central, collminated with the laser and popped the cap in and hey presto it now also shows it as colminated.

Getting two different results from something that should of achieved the same result would of really bugged me.

 

Dave

Edited by dnl
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As I said earlier in this thread, I've found that my simple cheshire eyepiece delivers results that check out when the scope is star tested (the acid test for me) so thats what I stick with now.

 

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3 hours ago, johninderby said:

A good point. Unless you have a properly set up focuser a laser may not give very acurate results. Also if the focuser drawtube shifts as it moves more problems.


 

What johninderby said ..................👍

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I have a Saxon Laser colliminator 

What have found with that, it is a fraction under 1.25 inches in diameter, and can get a bit of play in it when aligning both  secondary and primary mirrors

John

 

 

 

 

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I had gotten a laser-collimator a while back, and touted as having a triplet-lens for a tighter spot; "next generation" it was purported to be.  It was purchased off of eBay for less than US$30.  It arrived mis-collimated, of course.  I made a jig for it...

114293212_laser-collimatorstand15b.jpg.2b15ef86811ad6a47b6336ce57eb6e0e.jpg

The unit touches no wood, only PTFE(Teflon); a strange thing I had crafted.  I replaced the set-screws with "thumb-screws", and only then managed to get it collimated...

1067452470_laser-collimatorstand17a.jpg.6cad1cb44155d99c0057508533e3f4a8.jpg

Afterwards, I used it to check a diagonal, and to align an achromat's focusser; that's all.  

Many years before, I had gotten this passive set of tools, from left to right: a Cheshire(without cross-hairs), a sight-tube(with cross-hairs), and an auto-collimator...

1224688085_Tectrontoolset.jpg.76c566fc66e02ba9aa89c2f9febfcdfd.jpg

Modern Cheshires with cross-hairs are actually combination-tools, which is fine.  I want one, but I'm in no hurry.

I use the sight-tube when collimating, and a collimation-cap to tweak...  

265131397_081819-final.jpg.49796ed08776812967bbd2af96acdff2.jpg

At 50x per inch of aperture, I see glory, limited only by the atmosphere; with a 127mm f/3.3 to f/4 spherical-primary and a 4mm symmetrical-Ramsden to boot.

With larger, longer Newtonians and Newtonian-Dobsons, I suppose that there's merit in using a laser, in that our arms and hands and fingers will reach back only so far.  But then, how in the name of Newton was this collimated, and way back when...

AVGSagm.jpg

You get the picture, pun intended.

Edited by Alan64

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I expect the Earl of Rosse had a servant or two at the bottom end of the scope to tilt the primary while he was observing a star.

Adjusting the secondary must have been risky though !

 

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I use a compression fitting on focuser insert laser so it’s lightly holding but still be able to turn then watch laser on primary so it spins around polo mark on mirror  , adjust to suit  if lasers out it becomes irrelevant ,then final check with Cheshire or colli cap 

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