Another way to collimate with a laser

[mike-h]

I recently replaced the donut shaped center sticker on my primary mirror. It turns out that it had been stuck on 4mm off-center at the factory. I had an idea that a cross may work better than a donut for collimation with a barlowed laser.

I made a little cross out of 2 tiny bits of white sticker. I hoped that the shadow of the cross would reflect back on the laser collimator window when the laser is put into a barlow lens. It does! This means that I'm getting a genuine reflection centred (rather than the potentially less accurate return beam). It turns out that my Revelation laser collimator gave a very accurate return beam anyway, but it's good to see the evidence.

The pictures show

1) a view down the scope at the cross sticker on the primary

2) the (non-barlowed) laser beam hitting the centre of the cross (for collimation of the secondary) - and my chin!

3) the return shadow of the cross once the laser has been put into a barlow lens.

Any thoughts? It seems to work really well.

You can even see the return shadow without using the barlow lens but its fainter due to more red light return.

The only issue I've had is that if you're checking your secondary in the dark then the non-barlowed laserbeam dot hitting the center of the sticker makes seeing the red dot more difficult. However, if you shine a torch down the tube the little red dot becomes easy to see.

Mike-h

[mike-h]

Does anyone think this would be any use to beginners with fast focal ratio scopes?

Is it flawed in some way?

Mike h

[Sam]

This is a very useful idea. The cross pattern on the return that is displayed on the laser looks to be a very good feature. Repositioning the sticker in the centre (or replacing it as you have done) is a fairly common problem with the factory fitted stickers. Great idea - thanks for posting.

[ringz]

Well I hope that the optical centre and the physical centre of your mirror are coincident

Does anyone know the method manufacturers use for sticking centre circles on mirrors?

--

Martyn

[mike-h]

There's a thought. I thought the centre of the primary was just the centre. I know about offset etc...

Must say though that the collimation seems the best I have had so far with nice symmetrical in focus and out of focus rings.

Maybe someone else can clear it up.

Mike -h

[Sam]

There's a thought. I thought the centre of the primary was just the centre. I know about offset etc...

Must say though that the collimation seems the best I have had so far with nice symmetrical in focus and out of focus rings.

Maybe someone else can clear it up.

Mike -h

well there's the proof it works then!