RE: [APML] Film Thickness and Focusing

["Thom Iwancio" <tiwancio@sc.rr.com>]

Thanks Jerry and Kevin. 
I actually got my research started with Jerry's page on using a scrap of
film to make a knife edge focuser.  I like the ronchi screen method a
little better and have access to a full machine shop and gutted an in-op
OM-1 body so I can make things as accurate as I want, I just didn't want
to be wasting time "gilding a lily".  (As if the skies have been clear
in the Southeast)

Thanks,

Thom Iwancio
Elgin, SC
www.machunter.org

-----Original Message-----
From: astro-photo-bounces@seds.org [mailto:astro-photo-bounces@seds.org]
On Behalf Of Kevin Wigell
Sent: Tuesday, May 20, 2003 8:58 PM
To: Discussion of Film Astrophotography
Subject: Re: [APML] Film Thickness and Focusing

Thom, just to prove that I really have been doing my homework:

Jerry Lodriguss's CD/book (which I'm about half-way through reading)
says that Chuck Vaughn recommends putting some high-quality Scotch tape
on the pressure plate to make up for the difference in thickness when
using thinner Tech Pan. This is supposed to not only keep the film plane
in the same relative position (if focus is that critical), but to help
keep the thin Tech Pan flat as well.

Kevin Wigell
www.kwastronomy.com

----- Original Message ----- 
From: "Thom Iwancio" <tiwancio@sc.rr.com>
To: <astro-photo@seds.org>
Sent: Tuesday, May 20, 2003 20:19
Subject: [APML] Film Thickness and Focusing


> Hey all, getting tired of the "by guess, by golly" focusing method but
> lacking the funds for a real focus aid I have been researching the
> various homemade knife edge and ronchi screen focusers.  
> 
> My question is what is the depth of focus(field?) for an 8" f6
> combination?  I ask because today I took some film to work and
measured
> the thickness of the leaders using some precision gauging in our
quality
> lab. My results were:
> Elite Chrome 100 .0061
> Elite Chrome 200 .0062
> Old (good) Supra .0060
> Tech Pan .0040
> 
> Do I need to create a set of shims for the difference between Elite
> Chrome 200 and Tech Pan?  These are my two primary films.
> 
> As always, thanks in advance.
> 
> Thom Iwancio
> Elgin, SC
> www.machunter.org



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