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

["Jim Janusz" <jjanusz@dc.rr.com>]

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

----- Original Message ----- 
From: "Brian larmay" <power_windows4789@yahoo.com>
To: "APML" <astro-photo@seds.org>
Sent: Wednesday, February 04, 2004 10:16 AM
Subject: [APML] Red filters and the need to focus


> Does anyone know whether I need to calibrate my lens
> for a deep red filter that is not H-a?
>
> Im guessing mine is a #23 since there are no #'s on it
> besides R-2.
> Customer support is auomated and offers no help.
>
> When does one ned to calibrate, and when does one not
> need to calibrate?
>
> Just for another referance, here is a shot taken by
> someone else with an R-2
>
> http://astrophoto.westhost.com/Cygnus100mm_Tp.html
> I sent this guy an email about i, but it was returned
>
> Brian
>
> =====
> Homepage: www.astrobri.com
>
> Location:
> Niagara Falls USA
> geographic Longitude = 79W
> Geographic Latitude = 43N
> Corrected Magnetic Latitude = 53N
>
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