[Leica] How IR filters affect M8 B&W

[pklein at 2alpha.net (Peter Klein)]

George, Steve, and the gang:  You are quite right that this is a 
quick-and-dirty hand-held test, and *by itself* isn't scientifically or 
statistically valid "proof" of anything.

However, it is consistent with some other tests I've run (for focus shift) 
with other lenses, when the camera *was* on a tripod.  These were done 
with staggered cereal boxes and soup cans on the roof of my car. I never 
worked these up for posting, as they were just tests I'd done for myself 
to see how much my lenses focus shifted at various stops, and I did a 
couple of runs without a filter just for fun.

I've also done such tests under florescent light, and there was not much 
difference at all with/without the filter. Which makes sense, as 
florescent lights put out a couple of narrow bands of blue and green, and 
little else.

Taken all together, I feel confident that B&W shots I've just posted show 
an effect I've observed numerous times under more controlled conditions. 
And since I shoot wide open under tungsten light a lot, the results are 
quite valid for me. My practical-cat working conclusion is that the more 
IR reflective the subject is, the more IR light there is, and the wider 
the lens is, the more IR-smearing effect your're going to get. Based on 
that, I'm going to use the filters most of the time.

Another interesting aspect to all this:  Some might prefer the look of the 
shot without the IR filter.  It reminds me a bit of old-fashioned thick 
emulsion film with heighened red sensitivity, developed in D-23.  If you 
like that look, here's a way to get something like it digitally.

--Peter

George wrote:
> Peter's test shows us what this lens will do wide open, hand held, by
> Peter, at a 360th of a second, with and without a filter.

> Locking the camera down on a solid tripod, stopping down to where the
> IR wave lengths will also be in focus "may" very well provide a
> different result. All of us with M8's could spend time testing our
> various lenses, with and without filters, at various apertures,
> focused on various subjects, with various amounts of IR present.

> When discussing sharpness and contrast camera movement and subject
> movement must be absolutely removed from the equation (as much as is
> humanly possible).

> Peter's test, while interesting and informative, certainly did not 
> reduce camera and subject movement to anywhere near zero.