Can you insert a lens system to make an artificial star appear at infinity?

[Stonius]

I want to do some experiments with colimation, but in lockdown, I don't have access to much outdoor space. I'm wondering if I put, say a reversed barlow between the scope and the artificial star, maybe I could 'push it back' so my 6m hallway is long enough to achieve focus?

Or if not a barlow, any other lens systems that would project the star at infinity?

Cheers

Markus

[miker]

Hi Markus,

In this Cloudynights thread they use a mirror to increase the distance.

https://www.cloudynights.com/articles/cat/user-reviews/the-easy-way-to-align-your-telescopes-optics-indoor-artificial-star-collimation-r2798

Good luck

Michael

[Stonius]

Hey, that's a good trick! Pity I don't have any old secondaries laying about :-(


I wonder how accurate the shape needs to be or whether any convex surface would do. I have an old 60mm refractor objective. Maybe I could try to get a reflection off that.


Markus

[Gary47]

Harold Suiter in his book on star testing describes testing using Christmas tree ornaments to reflect a light source and gives the math to calculate the required point size.

[Stonius]

Of *course*! That's it! I happen to have just the thing from doing 360 degree HDR photography.


Cheers


Marks