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

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

Good point.  I missed that detail.  So does
it make sense to simply replace the camera's 
ground glass with a grating? 

----- Original Message ----- 
From: "Jerry Lodriguss" <jerry@astropix.com>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Sunday, July 20, 2003 4:08 PM
Subject: Re: [APML] 35mm focusing - using a ronchi grating in filter holder?


> 
> 
> This won't work.
> 
> The Ronchi screen has to be at the focal plane which is where the film is 
> supposed to be.
> 
> Jerry
> 
> 
> 
> 
> At 04:02 PM 7/20/2003 -0700, you wrote:
> >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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> 
> The book "Photoshop for Astrophotographers" is now finished!
> 
>   Go to: http://www.astropix.com/PFA/PFA.HTM
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
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