help for auto-collimator ronch source

[skybadger]

Hi all 

I am putting together an oil-bath auto-collimator rig to check over my reflectors. 

It occurred to me to use an off-axis guider body and its pick-off prism to feed the light source in - no heath robinson pipe assembling. Then I can just use a positive eyepiece where the camera should go to examine the ronchi lines to estimate the optics quality.

This raises the question  - I would need to put the ronchi screen on the telescope side of the prism - say in a filter mount . Is this too far from the source ? Is the source to ronchi screen distance important ?

Cheers

Mike

 

[James Vincent]

Hi Mike

Is it possible to draw out the ray diagram of the proposed set up  i am a little confused.

The Ronchi screen  is usually positioned where the the knife edge would have been.

[skybadger]

Hi James

Imagine the source and eye side by side looking towards the mirror. Further imagine the ronchi screen now an inch ahead of both. 

The question is  - what is the impact of the ronchi screen being so far forward ?

Cheers

mike

 

[mapstar]

Hi Mike

Is there an advantage to the set up over a normal Ronchi/knife edge tester where the eye is positioned behind both? 

I've seen auto collimation (null testing) done with an optical flat is this a similar set up? Or similar to a bath interferometer? 

Damian