[Leica] How IR filters affect M8 B&W

[afirkin at afirkin.com (Alastair Firkin)]

This is very interesting: I would not have thought the sharpness would be so 
different. The IR effect may help in shadows, but in pure sharpness, this is 
very challenging. I was told that the IR filter over the sensor could 
diminish the detail a little, so perhaps we are better off with the IR 
filtering on the front of the lens, or built into the lens.

Cheers

--- pklein@2alpha.net wrote:

From: Peter Klein <pklein@2alpha.net>
To: lug@leica-users.org
Subject: [Leica] How IR filters affect M8 B&W
Date: Mon, 16 Jun 2008 23:20:10 -0700

Steve Barbour wanted to see an A/B comparison of an M8 shot with and 
without an IR filter.

My newly-acquired VC 35/1.2 arrived today (yeah, I bought one). While I was 
checking it out, I took the same wide-open shot without an IR filter (left) 
and with the filter (right).  Tungsten lighting, three 40w bulbs above my 
bathroom mirror.

http://users.2alpha.com/~pklein/temp/IRNofiltVsFilt.jpg

Here's the whole frame of the IR filtered shot, uncropped but greatly 
reduced, for reference.
http://users.2alpha.com/~pklein/temp/IRFiltFullFrame3382.jpg

I stood on the exact same spot with both feet, and focused on my eyeball 
for each shot.  Shot RAW, converted in Capture One with the JFI Plain BW 
profile.  Identical exposures, 1/360 at f/1.2.  Default Capture One 
settings, so the same amount of sharpening was applied to each.

Notice the differences in tonal rendition and contrast, not to mention the 
sharpness of my eyelashes and receding hair line...   :-)  This is 
completely consistent with other test shots I've made with other lenses on 
a tripod. Since it shows a real person rather than cereal boxes or soup 
cans, I thought it would be a reasonable real-world demonstration of what 
happens.

The IR makes the skin a little lighter, and reduces the sharpness and 
contrast a little.  You might be able to play with local contrast and get 
back some of the crispness of the filtered shot, but the differences in 
rendition between the filtered and unfiltered shots remain.

All other things being equal, I prefer to use the IR filter while shooting 
B&W with the M8.  However, I have noticed that you can often gain a half 
stop more exposure without the filter, especially in reddish tungsten 
light.  So if I was shooting at 1/15 or slower, I might remove the IR 
filter, figuring that the half-stop faster shutter speed I'd get might gain 
me more in clarity than the IR smearing would take away.

--Peter


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