Re: [APML] Red filters and the need to focus

["John C. Mirtle" <spampit@shaw.ca>]

Thanks for the plug Jim and Bill! Brian, it's worth doing the test for all
the reasons mentioned so far. I use 3 different filters on my 180mm, they
all focus in different places. The difference isn't much but it does show
with tech pan! I haven't focused with 2 different red filters but there are
enough variables that you will want to confirm before blowing a good night
on un-focused shots.

John Mirtle
Calgary, Ab. Canada

----- Original Message ----- 
From: "Jim Janusz" <jjanusz@dc.rr.com>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Wednesday, February 04, 2004 5:10 PM
Subject: Re: [APML] Red filters and the need to focus


Hey Brian,

The very best way to calibrate the focus of a red filter is the photographic
method that John Mirtle describes on his web site.  Anything else is just
close.

http://members.shaw.ca/jmirtle/ha.htm

Jim

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