[APML] 35mm focusing - using a ronchi grating in filter holder?

["Jeff Crilly" <jlcphoto@myrealbox.com>]

I was looking at the van slyke page today, and came
across this little nifty "filter slot adaptor".

Its threads to a visual back and allows one to "drop"
filters in the light path.

And its inexpensive (for asto stuff).

I got to thinking that one could drop in a ronchi grating and
use it to find the focus with a film camera.  
(sorta like a stilleto.)

Since the ronchi will be projected on the ground glass
it might be acceptable on bright stars, etc.
I would need to assume that the film plane and the 
ground glass are at the same distance from the
T adapter (which should be and could be verified seperately.)
If not then a stilleto makes more sense.

Would this work?  

jeff



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