Laser collimator out of collimation?

[Robh]

I'm new to IceInSpace, so I don't know if anyone's brought this up before.
My previous telescope was a refractor. A few years ago, I bought a 12" Meade truss DOB and they recommended I use a laser collimator for quick collimation of the telescope. It was quite a while before I realised the laser collimator I was using (supposedly factory alligned) was itself out of collimation! And no, I have never dropped it!
I now use a cheshire for the final collimation but I was wondering how many people out there use a laser collimator and have ever bothered to check it for collimation.
Warning! With the laser on, make sure before you look down the telescope tube that the laser beam hasn't missed the secondary mirror and isn't shooting out the main tube! Holding the collimator firmly against the focuser draw tube and rotate it 360 degrees. If it's way out, the laser red dot will be seen to rotate in a circular path on the primary mirror. That's what mine did.
The instructions for the laser collimator basically says "do not fiddle with".
However, this is rubbish and I successfully collimated mine.
Go here, if you want to check or adjust your collimator ...

http://www.cloudynights.com/item.php?item_id=520

[GeoffW1]

Hi,

Yes, I made one just like this, it works well for me.

There has been a lot posted here on IIS on the subject, so you may be interested to read about it.

http://www.iceinspace.com.au/forum/search.php?searchid=1025187

Some laser collimation units are manufactured to be very robust, and are said not to require regular collimation themselves, although they cost a bit more. I have no experience with those.

I have the cheaper kind of unit from Bintel

https://www.bintelshop.com.au/Product.aspx?ID=6737

and have found this with it:

- the laser dot actually is an oval, an effect of the simple pen laser unit in it
- changing the batteries causes it to go out of alignment
- turning the laser on/off screw too much can cause it to go out of alignment. I try to turn this screw only just enough for operation when on.

Keeping all that in mind, I have found it suits me well. I find it is very reassuring to be able to gain some idea of whether the laser unit is pointing straight.

This jig method is not perfect though. For instance, it supports the laser unit at 4 places (in 2 V-blocks), whereas when in use, it is supported only circumferentially at one end. So this could introduce an error. Also, the jig is usually made of wood, which is not exactly precision stuff.

Out of curiosity I took my Bintel laser unit to a measurement lab where I worked, and measured the runout (or concentricity error) between each end of the laser housing, and found the error to be about 0.01mm.

That error translates to a "wander" of the laser dot of about 0.5mm over the 6m distance from the alignment jig to my garage door, which is where I measure the alignment or lack of it. So it is negligible in my case. Given the fuzziness of the laser dot and its shape I was satisfied with that.

Cheers

[Robh]

Thanks GeoffW1.

There is certainly heaps there from your link. I'm still reading.
Interesting that you could buy the green laser pointers and get a decent laser dot but these collimators give anything from an oval to an almost flat bar like mine, which was a Bintel as well.

[White Rabbit]

I check mine on a regular basis, I switch it on and look directly down the beam to see if it's coming out of the collimator straight, if it is then it's colimated. I've had to start using the other eye of late because I seem to be going a bit blind in my left eye, that was my good eye and the one I use to use for collimating my laser collimator. I should go to the doctors to get that seen to. I wonder what could be causing my blindness?

Ha, only kidding. Kids never do that at home everyone knows that lasers are for pointng a airoplanes and not your eyes.