Barlowed laser collimation

[Ally8446]

Right then I'll be quick with this one. I've got a Baader laser

colli iii. I know how to collimate using the laser which incidentally is brand new (after sending my old one back cos it went out of collimation). After doing a normal laser collimation I then tried the barlowed method and to my surprise the diverged beam on the primary was at least 8mm off the centre ring. I fiddled and tweaked and went through the whole collimation process again...... Same result. Can anyone possibly enlighten me please. Cheers folks.

Ally

[ScottS]

I think maybe you've got a bit of focuser slop there which changes (in terms of your beam angle) when you put the Barlow in the focuser. Have you collimated your secondary using the laser, as this can introduce errors also.

[andyman]

Hi ally 

For one i would not use a laser to collimate the secondary due to slop in the focuser it will give inconsistent results

I use a colli cap for secondary and barlow primary works for me.Have you tried ignoring the view from secondary mirror when barlowed and just adjusted the primary mirror so the enlarged donut is bang centre on the collimater window.Then put the laser back in with no barlow and see if what thats like

[andyman]

You could put some tape around the collimator barrel to make it a snug fit in focusser  

[Ally8446]

Hi ally

For one i would not use a laser to collimate the secondary due to slop in the focuser it will give inconsistent results

I use a colli cap for secondary and barlow primary works for me.Have you tried ignoring the view from secondary mirror when barlowed and just adjusted the primary mirror so the enlarged donut is bang centre on the collimater window.Then put the laser back in with no barlow and see if what thats like

I also always use a colli cap for secondary collimation, it's the simplest method, just wanted to try the barlowed laser method for the primary. I'm pretty spot on with manual collimation on the whole, star test etc but thanks for the advice, will try it asap.

Clear skies

Ally

[cotterless45]

Collimate with a Cheshire, colli cap , star test or by eye.

The Barlowed collimated laser is a superbly accurate check on your collimation. Not only will it account for your focuser slop, but it is superb to use in the dark. This will give spot on collimation which will make a Newt a planet killer.

For truss Dobsonians it is worth checking on construction and when in use. I've found that it can be off with temperature change and tube flex in light tubes. For deep sky fuzziness accurate collimation is not a big deal. For seeing details of Saturn's rings, Jupiter's belts and the surface of Mars , then it is most critical,

Nick.

[Ally8446]

Collimate with a Cheshire, colli cap , star test or by eye.

The Barlowed collimated laser is a superbly accurate check on your collimation. Not only will it account for your focuser slop, but it is superb to use in the dark. This will give spot on collimation which will make a Newt a planet killer.

For truss Dobsonians it is worth checking on construction and when in use. I've found that it can be off with temperature change and tube flex in light tubes. For deep sky fuzziness accurate collimation is not a big deal. For seeing details of Saturn's rings, Jupiter's belts and the surface of Mars , then it is most critical,

Nick.

I don't think I've done a very good job of explaining myself, so I'll try again.

Even though I know my collimation is pretty spot on when I do it with a colli cap and Cheshire, I like to check it with the laser. Today I tried the barlowed laser method AFTER I had collimated using the cap etc. What I don't understand is why, with near perfect collimation, the diverged beam showing on the primary was nearly 10mm away from the doughnut.

Hopefully I've done a better explanation this time lol