Laser collimation

[wookie1965]

As many of you know the cheaper lasers are usually not collimated I have just read a thread about checking your laser using a mirror (flat) to see if the laser light comes back and down the centre hole. 

Has anyone read this and what do the more experienced people think. 

[Ricochet]

I think it would be quite difficult to ensure that the laser is precisely perpendicular to the mirror surface. Any discrepancy will result in the collimated laser beam missing the hole. I've not seen the thread so perhaps an easy method to solve this is part of the method. 

[Franklin]

I've seen that method used to check diagonal collimation. I think for it to work you would really need to use an optically flat mirror, such as the secondary from a newtonian.

You can check the lasers collimation if you have a rotatable focuser on a refractor or, as I do a Baader fine focuser, and just fire the laser through the scope onto a piece of paper on a wall. When turning, it should not move.

Edited October 31, 2021 by Franklin
addition

[wookie1965]

Here is the thread. 

https://www.cloudynights.com/topic/745479-barlowed-laser-collimation-10-f5-step-by-step/

[Ricochet]

I wouldn't use that method to check collimation of the laser. By holding the laser against the glass face of the mirror the laser beam path length is reduced to about 5 centimetres, which is no where near long enough to check the accuracy of the laser. When I have collimated a laser I have set it up in a v block and used a target over 5 metres away. Additionally, it is actually very difficult to make optically flat mirrors and so household mirrors are not actually flat they're just close enough for general purpose use. 

[Louis D]

That's also not going to work for older lasers without a side port cutout like my AstroSystems one.