Hi William,
I can't give you an answer on where to
buy 48MM filters, but the IR blocking filter
is necessary when
a) your film (STV) will reach into IR (doh)
b) your lens has a different focus position
for red and blue light.
So if you are using, for example, a Newtonian
telescope, than all light focuses at the same
position. Many refractors will focus over a
range-and most OM lenses are refractive.
However, you mentioned that your Dad is using the STV.
I believe that this camera is very IR sensitive, which
will cause a halo around bright objects, especially
if used with poorly made reflectors or glass in the
optical train. Did you say you wanted to buy your Dad
a telescope with Fluorite element$$$$ ;-))
Date: Tue, 4 Jun 2002 10:04:18 -0400
From: William Clark <wclark@xxxxxxx>
Subject: [OM] OT: Colour filters needed..where can i get them
Given the expertise of list members, I thought I would post a filter
question having to do with astronomy.
Does anyone know who makes 2 inch (48mm filters) now? My dad wants to use
them as a "colour wheel" for an STV. I have checked for him and cannot
seem
to find appropriate tri-colour filters. Optec sells some, but I wanted to
price compare. I also called Lumicon, but they "can't get them anymore"
Any ideas here? Orion also has them, but the RGB filters are not the right
ones for colour separation (the green was is ok though #58).
Also, is an IR blocking filter really necessary for astrophotography? It
better for CCD or film? I wouldn't have thought colour film would need an
IR blocking filter.
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