Re: [APML] Tech Pan/Ha filter focusing

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

Hi Scott,

I would say no.  The Ha filter will shift focus towards the Ir as well as
the glass thickness.  Focusing for Ha is best done photographically using
some type of scale on the instrument.  See John Mirtle's page for a great
article on this.

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

Sorry.

Jim
----- Original Message ----- 
From: "Scott Hammonds" <capella@creatorsview.com>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Wednesday, June 04, 2003 11:47 AM
Subject: [APML] Tech Pan/Ha filter focusing


> Hey Tech Pan Junkies,
> This question may have been addressed before, forgive me if it has and
> for being too lazy to search the archives.
>
> I assume one day the weather will actually be clear again and I'll be
> able to shoot some film. I just ordered a 48mm Ha filter to use prime
> focus with my 4" scope. Can I use my IDAS filter to focus and then just
> replace it with the Ha filter and achieve accurate focus?
>
> Any help would be greatly appreciated.
>
> Thanks,
>
> Scott Hammonds
>
>
>
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> Astro-Photo@seds.org
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>


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