Laser collimator for skywatcher skyliner 200P?

[russ.will]

Ok, stupid question coming up. If I don't have a laser how do I align the primary when I'm standing in the dark? Do I shine a torch at the Cheshire target area?

For starters, I've had four Newts of one description or another and not one of them has actually had a perfectly centered center spot on the mirror - A point people don't realise. If you are assuming a laser will give perfect collimation, then you'd better check that what you're aligning it with, is accurate in the first place.

I'm also assuming that you have squared your focuser and correctly aligned the secondary. If you have, then these are unlikely to move, unless you've done something odd with a squishy material like a milk bottle or Bobs Knobs.

Simply put; You use a defocused star and this is, without doubt, the best way as it ignores inaccurate spots, bent lasers, etc.

Defocus on a bright star (any will do in a tracking scope, otherwise use Polaris) and see if the secondary shadow is off-set. If it is, move the star (by moving the scope) until the image does look concentric. Then, adjust the bolt on the primary that moves the off-center image back to the middle. This is normally enough. If it's not concentric (and it will be better than before), repeat the above steps until it is.

No lasers, no Cheshire collimators, just the only test that matters, it's free and it's best done in the dark.

Russell

[Dave In Vermont]

I have the Orion LaserMate Deluxe II. It arrived in perfect collimation - and is warranteed to remain so or they'll take them back. It works perfectly. And this on my 200mm F/4. I also use a Cheshire/Sighting-Tube. They both are in perfect agreement. Once center-marked, the laser allows full adjustment of the secondary, and the primary following the secondary. It's utterly simple to do - once you know how and understand fully of what you are doing - and why.

Without understanding the principles of a process, you are just following a recipe. This might be fine for boiling eggs to make hard-boiled eggs. But in, say, a chemistry lab - you'll likely blow yourself into the ionosphere.

Clear Skies,

Dave

[Coastliner]

I think I may have had a brainwave ( although the wave wouldn't have that far to travel ).

I've just been reading up on Barlowed laser collimation, and it seems to me that I can make a barlowed laser without having to buy a laser collimator. Given that the Barlow is there simply to diffuse the laser light so that it sprays the center of the primary, it seems to me that any old laser will do, as this method does not care about focuser slop, or laser collimation. So I will be off to Tesco this morning to buy a cheap keyring laser which I will fit inside a junk 2x Barlow that I have.

In fact, does it have to be a laser? A bright led torch shone down the Barlow should throw enough light through the central hole in the Barlow's faceplate to produce the silhouette of the doughnut back on the faceplate.

Some experimentation coming up, I'll let you know!

[Jason D]

For starters, I've had four Newts of one description or another and not one of them has actually had a perfectly centered center spot on the mirror - A point people don't realise. If you are assuming a laser will give perfect collimation, then you'd better check that what you're aligning it with, is accurate in the first place.

I'm also assuming that you have squared your focuser and correctly aligned the secondary. If you have, then these are unlikely to move, unless you've done something odd with a squishy material like a milk bottle or Bobs Knobs.

Simply put; You use a defocused star and this is, without doubt, the best way as it ignores inaccurate spots, bent lasers, etc.

Defocus on a bright star (any will do in a tracking scope, otherwise use Polaris) and see if the secondary shadow is off-set. If it is, move the star (by moving the scope) until the image does look concentric. Then, adjust the bolt on the primary that moves the off-center image back to the middle. This is normally enough. If it's not concentric (and it will be better than before), repeat the above steps until it is.

No lasers, no Cheshire collimators, just the only test that matters, it's free and it's best done in the dark.

Russell

if the tilt of the secondary mirror is off then no matter how you adjust the primary mirror, you can't get it right. There is no reasonable method to adjust the secondary mirror tilt with a star test. 

Even when the secondary mirror tilt is perfect, the star test can collimate the primary mirror but it might not be as good as collimating it via quality collimation tools. That is, star collimation can get the primary mirror focal point to the coma "free" zone under the eyepiece but it might not move the primary focal point at the center of the coma "free" zone.

Using quality collimation tools with a well-placed center mark is the most efficient method for accurate collimation.

Jason 

[Jason D]

I think I may have had a brainwave ( although the wave wouldn't have that far to travel ).

I've just been reading up on Barlowed laser collimation, and it seems to me that I can make a barlowed laser without having to buy a laser collimator. Given that the Barlow is there simply to diffuse the laser light so that it sprays the center of the primary, it seems to me that any old laser will do, as this method does not care about focuser slop, or laser collimation. So I will be off to Tesco this morning to buy a cheap keyring laser which I will fit inside a junk 2x Barlow that I have.

In fact, does it have to be a laser? A bright led torch shone down the Barlow should throw enough light through the central hole in the Barlow's faceplate to produce the silhouette of the doughnut back on the faceplate.

Some experimentation coming up, I'll let you know!

The laser beam has to be coincident with the barlow negative lens axis for best result. Well, to be more accurate it has to be parallel to the negative lens axis but it can't be too far from the axis; otherwise, the diffused laser will not cover the entire center spot. Furthermore, barlowed laser can't be used to adjust the secondary mirror tilt.. 

Here is a link to "Krupa collimator" that works similarly to a barlowed laser but without a laser and without a barlow.

http://www.iceinspace.com.au/63-355-0-0-1-0.html

Jason

[Coastliner]

The laser beam has to be coincident with the barlow negative lens axis for best result. Well, to be more accurate it has to be parallel to the negative lens axis but it can't be too far from the axis; otherwise, the diffused laser will not cover the entire center spot. Furthermore, barlowed laser can't be used to adjust the secondary mirror tilt.. 

Here is a link to "Krupa collimator" that works similarly to a barlowed laser but without a laser and without a barlow.

http://www.iceinspace.com.au/63-355-0-0-1-0.html

Jason

Agreed about the secondary, that will have to be done with the cheshire. As regards the laser axis I plan to mount the laser centrally in the barlow.

[Coastliner]

Jason, that is a nice link (Krupa collimator). Looks as though somebody beat me to my brainwave!

[Jason D]

Agreed about the secondary, that will have to be done with the cheshire. As regards the laser axis I plan to mount the laser centrally in the barlow.

Centrally is not as important as parallel. That is, you want to make sure that the laser beam is parallel to the barlow axis first then as close as possible to the barlow axis.

[Lowen22]

That video was great! I know what I'm going to be doing this afternoon.

[Astro_Baby]

Anyone up for making a Krupa collimator  ???  I lack thee tools to make that with any great accuracy.

[Coastliner]

I've had a go at making my own version of the Barlowed collimator, the showstopper was the fact that I could not see far enough up the drawtube to see if the silhouette of the doughnut was being projected on the card I glued to the end of the Barlow.

Any ideas anyone?

[Charic]

I used this method, ( www.youtube.com/watch?v=bE09_X43UUQ )  and have a similar Laser. Its now fully corrected for my needs, and can be purchased for under £20, mine was about £26!

Having the proper tool helps, and once set up and you know the limits,  the laser  should be of some use. having the best of both techniques for collimating.

[russ.will]

if the tilt of the secondary mirror is off then no matter how you adjust the primary mirror, you can't get it right. There is no reasonable method to adjust the secondary mirror tilt with a star test. 

Which I why I said:

"I'm also assuming that you have squared your focuser and correctly aligned the secondary. If you have, then these are unlikely to move, ....."

[Jason D]

I've had a go at making my own version of the Barlowed collimator, the showstopper was the fact that I could not see far enough up the drawtube to see if the silhouette of the doughnut was being projected on the card I glued to the end of the Barlow.

Any ideas anyone?

Use a mirror. See attachments:

[Jason D]

Which I why I said:

"I'm also assuming that you have squared your focuser and correctly aligned the secondary. If you have, then these are unlikely to move, ....."

I was responding to your last statement in the same post "No lasers, no Cheshire collimators," which gave me the impression you are not using any collimation tools. If you are going to use collimation tools to align the secondary mirror then you might as well finish the job of adjusting the primary mirror using tools. If you see inconsistency between the star test and the collimation tools then fix the problem. For example, accurately center the primary mirror marker or get better quality collimation tools. Once you get consistency then there will be no need to use star collimation which I find to be more cumbersome. Having said all that, to each his own. Everyone is free to follow whichever collimation method he/she feels comfortable with.

Jason

[lensman57]

I was responding to your last statement in the same post "No lasers, no Cheshire collimators," which gave me the impression you are not using any collimation tools. If you are going to use collimation tools to align the secondary mirror then you might as well finish the job of adjusting the primary mirror using tools. If you see inconsistency between the star test and the collimation tools then fix the problem. For example, accurately center the primary mirror marker or get better quality collimation tools. Once you get consistency then there will be no need to use star collimation which I find to be more cumbersome. Having said all that, to each his own. Everyone is free to follow whichever collimation method he/she feels comfortable with.

Jason

I have always said that the two most important bit of " help " that the manufacturers can give the user is 1- marking the centre of the primary accurately and 2- marking the centre of the focuser on inside of the tube something that is easily accomplished while the tube is being cut by the machine for the focuser. Once the focuser is adjusted to be orthogonal to the axis of tube, using  a laser or a Cheshire collimating EP, then the task of centring offsetting the secondary can be done easily and with confidence. The alignment of the primary is probably the easiest bit of the procedures and can be done is less than 10s even using a simple collimating cap.

A.G

[Coastliner]

OK, I have borrowed a friend's laser collimator and am coming down on the side of the cap/Cheshire method a la Astrobaby.  I've finally got to the point where I fully understand what is going on when I do the collimation, I can ignore the info. I don't need (reflections etc) at any stage in the process. I collimated accurately, got nice Airey rings and a central dot around a defocussed  star, then stuck the laser collimator in (having first checked the collimation of the collimator, which was spot on) and the laser missed its target by quite a bit. I adjusted the primary so that the laser hit its target, looked through the Cheshire and the primary mirror's doughnut was out by about the diameter of the doughut. This seemed to be down to the dreaded focuser tube "slop" - there is a lot less slop with the longer Cheshire tube.

BUT - my back was breaking by the time I had finished collimating with the Cheshire, having to go back and forth quite a few times. adjusting the screws, checking, more adjustment, etc.

So, Is the diameter of the doughnut a significant collimation error? If not, I will go for the Next Gen collimator and save my back. If it is a significant error I am very tempted to go for one of the HoTech self-centering collimators to stop me overdosing on ibuprofen. (Incidentally, Astrobaby gives a good review of the HoTech even though she doesn't like lasers, so I guess it must be good).

Any thoughts, anyone?

Neil.

[Charic]

You say everything was ok, before the Laser, so why bother with a Laser, save your money, buy another EP, less trouble!

Having assured my knowledge of collimation, on my Newtonian, I prefer the accuracy of a 'long' sight tube to align the secondary, and the Cheshire to align the primary.

Due to the fit of the Laser and any rotation, I can still present/show an offset spot, sometimes? if I dont handle the situation with care. However, I can ignore these errors if I Barlow the laser for a quick check away from home, prior to observing.

Even the most expensive designed lasers still require a concentric mounted secondary mirror. This must be centrally aligned to the focuser. Then tilt aligned to the primary, then the primary tilt aligned to the seconday, which must be aligned to the focuser.

Around in circles, I know, but thats how it is!

[russ.will]

...I collimated accurately, got nice Airey rings and a central dot around a defocussed  star....

Neil.

Then why worry about checking with a laser?

I've had refractors professionally double pass collimated and the quality of the observed airy disk is the definitive measure of the quality of collimation. If you've nailed that, throw the tools back in the case, get an EP out and start enjoying observing with a very well collimated scope.

It really isn't worth pursuing any further. You have an F6 Dob which is visual only and relatively un-fussy about collimation anyway. If it was some sort of F4 imaging astrograph, then that would be different. Obsessing over lasers and advanced collimation tools for your purposes, is like wondering which pair of slicks are best suited to the family Ford Focus.

Russell

[mdstuart]

As a visual observer. Even with an F4.5 scope I collimate by looking at a defocused bright star.. get to a position where the star looks round and the secondary is a blackdot in the centre...

Begin with the end in mind![emoji3]

Mark

[Coastliner]

Main reason for laser is, as mentioned, back problem - I really did find it painful to keep going back and forth, so the laser seems a good option, especially if the collimation is not that critical on the 200p. Point taken re slicks on a Focus, the SCA would be approaching half the price of the scope! So I think I'll end up with a Next Gen laser with masking tape around it to take up the slop.

[triton1]

Yes it works for me!

[Coastliner]

Yes it works for me!

It's you I got the idea from!

I've just ordered a Next Gen 7 brightness level colly, £17 inc. postage.

[Jason D]

 I collimated accurately, got nice Airey rings and a central dot around a defocussed  star, then stuck the laser collimator in (having first checked the collimation of the collimator, which was spot on) and the laser missed its target by quite a bit. I adjusted the primary so that the laser hit its target, looked through the Cheshire and the primary mirror's doughnut was out by about the diameter of the doughut. This seemed to be down to the dreaded focuser tube "slop" - there is a lot less slop with the longer Cheshire tube.

Neil.

1- Star collimation involves adjusting the primary mirror. Where the laser beam lands on the primary mirror is only depend on the secondary mirror adjustment. That is, there is nothing you could have done with star collimation that will cause the laser to deviate from the center. If you noticed deviation then it must have been due to some mechanical cause such as focuser slop, secondary mirror shift at different OTA elevation, ...etc.

2- You should never adjust the primary mirror to direct the laser back to its source unless the laser beam points at the center spot center.

3- Star collimation is not as accurate as quality collimation tools. If you fine tune collimation using a defocused star then I should not expect all qualify collimation tools to agree with it. Bear in mind that star collimation does not fix secondary mirror adjustment issues.

Jason 

[lensman57]

1- Star collimation involves adjusting the primary mirror. Where the laser beam lands on the primary mirror is only depend on the secondary mirror adjustment. That is, there is nothing you could have done with star collimation that will cause the laser to deviate from the center. If you noticed deviation then it must have been due to some mechanical cause such as focuser slop, secondary mirror shift at different OTA elevation, ...etc.

2- You should never adjust the primary mirror to direct the laser back to its source unless the laser beam points at the center spot center.

3- Star collimation is not as accurate as quality collimation tools. If you fine tune collimation using a defocused star then I should not expect all qualify collimation tools to agree with it. Bear in mind that star collimation does not fix secondary mirror adjustment issues.

Jason 

I have got the laser ( Baader ) to collimate the primary just prior to imaging after a long cool down and I trust this more than a star test. A star test is only possible under very good to excellent seeing conditions, something of a rarity under the UK sky. After a good laser collimation the star test looks good but not vice versa. I agree that the quality of the collimation tools is of essence. I have a short Chinese made Cheshire EP that is next to useless as the cross hairs are not centred nor are they perpendicular to each other.

A.G