[Leica] How IR filters affect M8 B&W

[hoppyman at bigpond.net.au (Geoff Hopkinson)]

Well done Peter, a very useful and practical illustration of the points that
you made. With a close up, wide open and all tungsten lighting you have a
worst case, certainly though. My initial impression on the extra 'light'
gained by removing the filter is that it would be slightly defocused less
useful light. I don't understand any benefit for not using the UV/IR, except
of course where you are deliberately seeking to simulate an IR effect as
though it was an IR film emulsion. The other exception might be if you had a
problem with reflection of specular light sources made worse by the
additional glass?

Cheers
Geoff
http://www.pbase.com/hoppyman/e
http://gallery.leica-users.org/v/gh/

-----Original Message-----
Subject: [Leica] How IR filters affect M8 B&W

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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