View Full Version here: : Inaccurate Laser Collimation??
EzyStyles
31-01-2006, 08:28 PM
Hi,
Just got myself a laser collimator. After accurately using it, now when looking down the focuser, it doesnt look aligned?
From the pic, it is the thick black ring with the red arrow pointing to it. You can see its not straight.
thanks
gaa_ian
31-01-2006, 08:40 PM
many of these laser colimators, themselves need collimating !
This because the laser module inside can get out of alignment with the casing.
I know there is an article on it somewhere, just cant lay my hands on it right now ?
rumples riot
31-01-2006, 08:43 PM
To check the collimator, make a jig out of timber with two pieces cut into a v. screw both pieces to a flat piece of timber and then place the collimator in the V's length ways. Get a piece of white paper and put it around 10 feet away and turn on the laser and point it at the paper. Mark the paper where the laser hits and then roll the laser 90 degrees. Repeat the first step and then roll again another 90. Repeat this until you have gone all the way around. Turn off the laser and look at the marks you have left. With any luck you will have a collimator that can be adjusted. If the collimator is out adjust it and then try collimating your scope again. If the collimator cannot be adjusted and it is out return it to the place of purchase and ask for another on.
gaa_ian
31-01-2006, 08:50 PM
Thanks RR, saved me saying all that !
I have found that the Orion/Andrews style lasers have a good outer casing.
However the internal module is a cheap $5 laser module you pick up at most discount stores :mad2:
Over tightening the screw that activates the module switch, can bend the PC board inside the module making the alignment way out !
Its fiddley but can be fixed by fitting a spacer to ensure the screw can not be overtightened.
RAJAH235
31-01-2006, 08:50 PM
Your 2ndary looks out of coll. Try the 'sheet of white paper bluetacked to the opposite side of the tube trick'. Adjust till it is centred in the focuser tube. Then go from this, >
http://www.fpi-protostar.com/collim.htm
:D L.
ps. Get a Cheshire site tube/combo. Much better than a laser for initial set-up. All you need really...L.
rumples riot
31-01-2006, 08:55 PM
No probs, had to type quick, just to get it done. lol
gaa_ian
31-01-2006, 08:56 PM
Thanks Laurie
Thats a good link, now in my book marks !
EzyStyles
31-01-2006, 08:58 PM
thanks for the help guys. where the red arrow is pointing, is that the focuser?
RAJAH235
31-01-2006, 09:06 PM
No. The reflection of the 2ndary. Use the link, Luke, use the link.....:D L.
EzyStyles
31-01-2006, 09:06 PM
The secondary was quite accurate actually. looking down the tube, the laser was hitting the center spot spot on.
Don't know if this has been posted before but If you have BB the following link is very good, it's a video on how to Collimating a Newtonian.
http://www.andysshotglass.com/Collimating.html
RAJAH235
31-01-2006, 09:31 PM
Ezy, from the pic, it appears that the 2ndary is not in the centre of the focuser tube. It should be. You have to move you head around a bit to line it up correctly. Use the white paper behind the 2ndary on the opposite side of the tube, as posted above.. Not thru the front of the t'scope...
Once again I'll say, use a film can or Cheshire. Do not rely on the laser...:D L.
janoskiss
31-01-2006, 09:44 PM
in response to your 1st question about this in the "2x or 3x barlow" thread: What do you mean, "look down the focuser? Do you have a basic collimating tool (Cheshire), a tube with a hole in the side exposing a 45-degree angled reflective surface, pinhole at one end and cross-hairs at the other end? That is what you should be looking through to check collimation, are you?
Ezy, I'm surprised Bintel sold you a laser instead of the basic tool. :confuse3: I'm curious who you talked to and what they told you about collimating.
I would look after that laser if I were you because you might want to take it back and exchange it for a more suitable tool.
EzyStyles
31-01-2006, 10:12 PM
Thanks for the reply steve. I don't think i have a Cheshire as i dont even know what that is. All i did was took out all the eyepieces in the focuser and look down it.
Spoke with Graham down at Bintel. The laser still in brand new condition as i only used it once. :P
janoskiss
31-01-2006, 11:35 PM
I don't really know Graham. What did he tell you about collimation? Did he show you how to use the laser? Did he explain its shortcomings and how to overcome them? Did he show/tell you about the alternatives to the laser (which experienced amateur astronomers prefer btw)?
Roger is the Guru at that shop. I always try to get his opinion on everything.
EzyStyles
01-02-2006, 12:10 AM
he did a demonstration on how to use the laser aligning the primary mirror from the adjustable knobs from the laser window. Other than thats about it. hmm should i go back tomorrow and return the laser?
johnno
01-02-2006, 02:15 AM
Hi All,
I Totally agree with RAJAH,
It looks to me also,the 2ndry is out of Collimation.
Looking at the pic,you can see it is way too far the the left,IE,NOT CENTRED.
Regards.
John
RAJAH235
01-02-2006, 02:33 AM
FWIW. Addendum, The camera angle may be slightly off centre, (lighting/lens is off centre), but I would still suggest using a Cheshire instead of the laser. Do the "mechanical" centres first. :D L.
barees63
01-02-2006, 07:03 AM
FWIW, here's a link to the simplest possible jig for collimating a laser collimator: http://home.earthlink.net/~celstark/id14.html
Bruce
That's both funny and very handy.
Thanks mate:lol:
janoskiss
01-02-2006, 03:09 PM
I must say I am somewhat disappointed about this. I expected a little better from Bintel... :shrug: This last step of the collimation (aligning the primary) is the easiest step and you don't need a laser for that. In fact, a laser is not as reliable as the simpler collimating eyepiece (even if it's one you make yourself from an old film canister). I take it you did not take your scope along to the shop.
The hard part is the secondary, but it does not need doing often. First you have to position it so it's centred when viewed through the focuser. This can be fiddly and a bit nerve-wrecking if you have not done it before. Then you have to align the secondary so it directs the optical path from the focuser onto the centre of the secondary. This is the step where a laser can be useful, but it is not needed. This too is a little fiddly, but not too bad. Just do it incrementally in small steps. It's not like the primary where there are springs that will pick up the slack so you can just keep turning the adjustment screws.
I hoped the Bintel people would have taken you through all this. Like I said, I don't know Graham, but Roger or Anthony should be able to guide you through the whole process from start to finish, and knowing Roger, he would be more than happy to help out and have you go home with your scope well-collimated. (You might have to wait depending how busy they are, of course. A customer already in there looking to buy a $5000 Goto scope will naturally have priority over someone who needs help with collimation and maybe a sub-$100 item, which is fair enough.)
Whether you want to return the laser or not is up to you. I see it as a beginner's item, perhaps less intimidating than a simpler passive tool, but ultimately it's a waste of money. I doubt it is accurate enough for your very fast mirror. This is what I'd get instead: Orion collimating eyepiece: https://www.bintelshop.com.au/Product.aspx?ID=5508
BTW: I have the laser, the long collimating EP (like the Orion one) and a short collimating EP. I started with the laser, but now only use the long coll. EP. If the laser itself lasts it's worth having as a backup, though. (it didn't in mine, but for you at least the shop is closeby and they can fix it if it seizes up.)
Here is something to try: Collimate with laser. Take it out of the focuser rotate it some. Put it back in, retighten in focuser. See if it still tells the same story. Do this several times to see how reliable it is.
There is a more advanced method using lasers, called the "barlowed laser" method. Roger knows all about that too. (That guy really seems to know just about everything about scopes.)
Good and easy to follow instructions on collimation are at the Sky & Telescope website.
Good luck & tell us how it all goes.
Hammerman
03-02-2006, 03:48 PM
Sky & Telescope magazine had an article in one of thier 2002 issues about a cheshire being more accurate than a laser, especially for the final steps of collimation. I have both an Orion Lasermate and an Orion Cheshire. I hardly use the laser any more as I've found out through trial and error that the magazine article was right.
barees63
03-02-2006, 04:51 PM
Just so you know, the laser units inside the most common laser collimators are replaceable for approx $2, they are exactly the same as the $2 keyring lasers.. I replaced the (dodgy) laser in my GSO collimator with one of these.
janoskiss
03-02-2006, 05:50 PM
Yes I know. I replaced mine with a $2 junk shop one. That's on its last leg now too and I don't think it's the batteries (but maybe). It is a real pain to replace and collimate the laser in these things. You are looking at several hours of fiddle time. And you might still wreck the new laser with too much pressure from the collimation screws. I just can't be bothered doing it yet again. Maybe I'll try new batteries but if that doesn't do it I'll just let it RIP.
Starkler
03-02-2006, 07:34 PM
The laser does have a use , and that is for final aligning of the secondary.
If the laser dot falls in the middle of the primary donut, you know that your focal plane will be exactly at right angles to the focuser axis.
Any error in secondary placement after this will be in terms of how off centre the illuminated field is.
janoskiss
03-02-2006, 10:57 PM
Someone here was recommending high quality laser collimators not so long ago. Maybe it was ausastronomer John?? Called something like "EZ" collimator?? I thought Bintel had them, but all they have on their website now is the cheapo Chinese unit that everyone else has. :shrug:
AstroJunk
04-02-2006, 12:43 AM
Nah, too many nails!
This is my rig - A vice and a 1.25 to 2 inch adapter. Simple as. Takes moments to align (depending on how far I have to walk to plot the poles:nerd: ).
At the end of the day, the only true measure of how good your alignlment procedures are lie in star testing. Once that secondary is sorted out, then a laser should do the trick in seconds. A barlowed laser even better. A cheshire - that works too (but are now more expensive than lasers would you believe).
Hammerman
04-02-2006, 04:37 AM
I really like your device, AstroJunk! I may have to give that a try since I already have all the parts.
Quick comment on your "cheshire more expensive than lasers" remark..... Here in the USA at Orion you can get the LaserMate for $50.95 and the Cheshire for $39.95. Are the cheshires really more expensive there in your part of the planet? I'm not doubting your word, I'm just suprised.
RAJAH235
04-02-2006, 05:07 AM
All depends on which brand you want as to price... My 'Orion' Cheshire cost AUS$60 or so about 6 yrs ago... Can get cheap one for AUS $29 now, but quality is diff.. :D L.
Starkler
04-02-2006, 08:54 AM
I used the block of wood and nails trick and it works a treat. Using the adapter as described above introduces an extra source of error that can shift the beam while trying to adjust the laser.
AstroJunk
04-02-2006, 11:18 AM
Yes, one has to tighten up the grub screw to get consistant results.
I wonder what cumualtive allignment error is introduced when stacking adapters and barlows etc when observing? But thats a diferent subject...
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