Re: Red enhancement

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On  2 Dec 99 at 10:30, Ibrahim PAMUK (Ank,IH) wrote:

> Hi,
> 
> I am wondering the effect of red enhancer to IR pictures? Can anyone comment
> on this and it would be lovely if he can have an example somewhere? 

Enhancement filters are more likely to decrease the IR effect than to 
increase it. In the visible range, they have an almost digital 
spectrum, with very sharp peaks and valleys....it's this rather 
erratic 'curve' that allows some yellow and orange tones to be 
blocked, while the underlying red tones are (relatively) 
pronounced....so this says nothing about the transmission outside the 
visible range....could be transparent, could be blocking, or could 
just as well continue to be very erratic, with no overall effect in 
UV and IR.

However, one of the sub notes I once read about them (TopShooters in
particular), is that they also block UV and IR....by how much, and
starting from what wavelength, I don't know.


> Maybe it is the time to ask the same question about infrared polarizer.

Normal polarizers are ineffective above 7-800nm....so while they 
might show an effect with HIE & a #25 red, they are quite useless 
with darker filters.
However, a true infrared polaroid filter is quite problematic....they are either 

1) opaque (hence the orientation can't be previewed with the naked
eye....might work with electronic cameras)

2) diffuse (slight optical imperfections, works only as IR light 
source, not for imaging purposes)

3) hideously expensive (about US$500 for a piece of 10x10cm)











 






 

--                 
Bye,

Willem-Jan Markerink


      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]
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