[ATMoB-discuss] Day Star Filters

[Paul A. Valleli]

Mike,
This question is best answered by a Daystar Rep
because there are many semantic variances.

Strictly, an IR blocking filter is one that blocks
all IR  from  7000 Angstroms  up to approximately 15
microns in the thermal IR. It can simply be a
coating applied to one lens surface or a separate
piece of glass. Usually the IR blocker is part of a
CCD but lately we are seeing manufacturers apply the
special evaporated coatings  to a lens surface. This
is true of  the  current Phillips Web Cam  and
Logitech .  This filter prevents IR  light to be
defocused by a non-Apochromatic lens and generating
a blur around the sharp visual image.

An Energy Rejection Filter  can have the  same
function  by simply limiting  the wavelengths that
are transmitted to the focal plane. A deep red
filter would do this but if it "turns - on" again in
the thermal IR, it could blind an eye. An ERF could
also be a metallized coating that reflects most
light energy rather than absorb it. A Herschel Wedge
can be thought of in the same sense because it
refracts most of the energy away from the eyepiece.

1. So the answer to question One is "sometimes".   
 

2. Question Two  - "it depends".  Some vendors use a
slightly  negative lens  to defocus any light so
that a real image of the Sun cannot be formed near
the eyepiece.  The other type of ERF for eliminating
the Near IR most commonly is placed near the focal
plane but far enough away so that minor dust specs
do not cast dots or 'doughnuts' on the detector.

I know this doesn't really answer the questions but
hopefully will give an understanding of why Daystar
needs to be contacted.
Paul

---- Original message ----

  Date: Fri, 27 Jul 2007 11:42:53 -0400
  From: noatak at aol.com
  Subject: [ATMoB-discuss] Day Star Filters
  To: atmob-discuss at atmob.org

  >
  >A?e-friend of mine from Bolivia has just acquired
  a T-Scanner Daystar solar filter with an IR
  Blocking filter?and has asked me some questions as
  to it's use which I cannot answer because I've
  never used one. If someone could answer these
  questions I would appreciate it and will pass the
  response along.
  >
  >Mike Hill
  >
  >
  >
  >1.? Will an IR Blocking Filter work the same as
  an energy rejection filter (ERF)
  >
  >2. Where is the proper place to put the IR
  Blocking filter.
  >
  >Any general comments as to it's use would also be
  helpful but these were the two questions posed in
  particular.
  >
  >
  >Thanks for any replies.
  >
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