Archived posting to the Leica Users Group, 2007/03/18

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Subject: [Leica] Ir filter and film cameras, take it off
From: red735i at (Frank Filippone)
Date: Sun Mar 18 17:02:26 2007
References: <> <00b401c769b1$733db420$59b91c60$@net> <>

I'm not completely convinced.....  It is true that the response of an 
absorptive filter depends on the thickness of the coating, and
at more oblique angles, the thickness IS more than at 90 degrees.  So there 
is a component of angle of view to spectral response.

However, if true, then someone in the past would have noticed the effect 
using some kind of film with some ultra wide angle lens on
some format including the same lens in question here and a Leica camera.  I 
have never heard of this in the film world.  Not that I
am all knowledgeable or all knowing.  But this fact missing gives me reason 
to doubt.

The B+W 486 filter I reviewed, had a reflective coating.  That means that 
instead of absorbing the frequencies of disinterest, it
reflects them back and forth between the coating layers.  The rays of light 
never go through the filter, except those in the pass
band.  This type of filter is significantly less susceptible to angular 
issues than the absorptive type, whereby all the rays go
through the complete thickness and therefore are affected more.

Taking this the next step, the only rays we capture on "film"  IS the pass 
band, so these rays do go through the filter and may be
affected by the angular issues already mentioned.

There is another issue... as I said when I corrected someone on the filter 
type, the 486 filter does have a rather strange response
curve in the pass band.  It allows a bit more blue light to pass than say a 
UV filter.  So it may just be that the specific filter
makers specs may be the source of the problem.....

BTW, your eye can may not see the areas at the edge of the pass band and 
especially the areas that might be causing the problem:
390nM and 690nM.  The human eye is good for around 400-700nM.  Some eyes go 

This is the write up of the B+W 486 filter........

B+W Digital UV-/IR-Blocking Filter 486 DIGITAL-PRO SLIM
This B+W Interference Filter has a completely colorless
glass carrier coated with a number of extremely thin, partially reflecting 
layers with precisely computed
thicknesses, similar to MC coating. The B+W Filter 486 does not block by 
means of absorption, but by interference of the unwanted
UV- and IR radiation
that is repeatedly reflected between these layers, affecting the wavelengths 
on both sides of the visible spectrum with a steep
cut-off. It is used mainly on digital- and video cameras with CCD sensors 
without an integrated IR protection filter, because the IR
sensitivity of the CCD sensor would otherwise
cause color changes and unsharpness. That unsharpness
results from the chromatic aberration of the lenses that are only corrected 
for visible light. In the visible range, the
transmission curve is very high and straight. This filter is completely 
clear and it requires
no increase in exposure. Its filter factor is ?.

Frank Filippone 

It has nothing to do with film or the brand of filter. The problem is  
the color response of the filter at extreme angles. If you take an IR/ 
UV filter in your hand. Look through it straight on. The color  
through the filter is quite normal. Then slowly rotate the filter so  
you are looking through it at an angle. The color through the filter  
will turn cyan. The sharper the angle, the more cyan.


Replies: Reply from henningw at (Henning Wulff) ([Leica] Ir filter and film cameras, take it off)
In reply to: Message from msadat at (mehrdad) ([Leica] Ir filter and film cameras, take it off)
Message from red735i at (Frank Filippone) ([Leica] Ir filter and film cameras, take it off)
Message from len-1 at (Leonard Taupier) ([Leica] Ir filter and film cameras, take it off)