Re: A Comment on the Lenses (part 2)

[Arne Henden <aah@nofs.navy.mil>]

I don't know of a stock IR-blocker that would remove the red tail
of a typical Bessell Ic filter.  A custom filter could be made,
but I bet it would be expensive.  If you have the space, then I would
suggest buying an interference Ic and placing it ahead of the
camera+window combination.  This places *two* I-band filters in
the light path, thereby decreasing the transmission through the
system, but at least you will have the proper passband.  This is
a simple test, though at the cost of a photometric filter.  You
could use the filter in some future camera, though.
Arne

Tom Droege wrote:
> One place to test this would be at the image end of the lens.  Here the 
> opening diameter is a little over 2" so anything larger than a 2" 
> diameter filter would do the job.  This would save tearing up a camera, 
> but would add two more surfaces to the optical path.  There is room for 
> something up to 1/2" thick here.