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Thread: How IR filters affect M8 B&W

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    Senior Member Peter Klein's Avatar
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    How IR filters affect M8 B&W

    My newly-acquired VC 35/1.2 arrived today. 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.

    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. The IR and visual components don't focus at quite the same place, so they are always out of sych with each other, degrading the image.

    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.

    From other tests I've made, the IR smearing effect seems the greatest in full sunlight and tungsten light, less so on cloudy days and under florescent light. And it might be less of an issues stopped down.

    --Peter
    Last edited by Peter Klein; 12th April 2010 at 19:32.

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    Re: How IR filters affect M8 B&W

    using the noct and the canon 85 1.2 I have learned one thing: dof is paper thin and inhaling changes the point of focus.

    When I look at the pic w/o Ir filter it seems to me you are a little back focused, see how your sideburn is very sharp? also your ear is more in focus and the camera strap more out of focus.

    looking at the pic w/Ir filter you eyeball is sharp but the sideburn is not. the ear is really falling out but the camera strap is more in focus.

    I think what you are seeing as a change in contrast is a change is focus.

    do it again with a tripod, although this will not stop you from breathing!

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    Senior Member LCT's Avatar
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    Re: How IR filters affect M8 B&W

    I would choose a slower aperture to avoid focussing issues personally.

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    Senior Member Peter Klein's Avatar
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    Re: How IR filters affect M8 B&W

    The forum software resized my picture. Here's a link to the original:
    http://users.2alpha.com/~pklein/temp/IRNofiltVsFilt.jpg

    Because the IR focuses at a different point than visible light, what appears to you to be a focusing error may actually be the effect of varying amounts of defocused IR combining with focused visible. I was very careful to do the "Leica sway" and press the shutter when my eyeball snapped into focus, both times. I can't be 100% sure about this of course.

    Look at the top of my hairline, which is further from the lens than my eyeball. If the issue was solely back focus on the left (no filter) shot, the hairline on the left picture should be sharper than on the right. It isn't.

    What I've posted 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 observed the same slight smearing without the IR filter.

    I've done the same thing with a piece of newspaper under tungsten light. The in-focus parts are less sharp without the filter than with it.

    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 continue using the filters most of the time.

    --Peter
    Last edited by Peter Klein; 17th June 2008 at 10:47.

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    Subscriber Member jaapv's Avatar
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    Re: How IR filters affect M8 B&W

    It is a nice demonstration of a known effect. Thanks for sharing
    It was actually known long before the advent of the M8. In the days before Leica used Absorban kit in their lenses, UV light would show much of the same results.
    JAAP
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    The colours of my generation are black and white.

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    Senior Member Peter Klein's Avatar
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    Re: How IR filters affect M8 B&W

    Exactly, Jaap. People are so used to UV filters and UV absorbing compounds in the lenses that they forget about things like the "blue haze" problem. Literature of the 1960s and earlier is full of such references, mentioning UV and "skylight" filters for color, and yellow and red (especially) filters for B&W.

    IR, like UV is simply light that we can't see. But film can "see" UV and the M8 can see both.

    I'm especially aware of IR because I had a job in a paint and coatings laboratory when I was younger. I ran an IR spectrophotometer. It was amazing to look at the spectral curves of various compounds. Two white powders that looked alike to us had completely different curves in the IR spectrum. All because of molecular resonances that affected light we can't see.

    As some folks said in the 60s, "it's all vibrations, man..."

    --Peter

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    Senior Member Daniel's Avatar
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    Re: How IR filters affect M8 B&W

    Peter,

    would you describe what you mean by IR smear?

    Dan

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    Re: How IR filters affect M8 B&W

    Quote Originally Posted by Peter Klein View Post
    The forum software resized my picture. Here's a link to the original:
    http://users.2alpha.com/~pklein/temp/IRNofiltVsFilt.jpg

    Because the IR focuses at a different point than visible light, what appears to you to be a focusing error may actually be the effect of varying amounts of defocused IR combining with focused visible. I was very careful to do the "Leica sway" and press the shutter when my eyeball snapped into focus, both times. I can't be 100% sure about this of course.

    Look at the top of my hairline, which is further from the lens than my eyeball. If the issue was solely back focus on the left (no filter) shot, the hairline on the left picture should be sharper than on the right. It isn't.

    What I've posted 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 observed the same slight smearing without the IR filter.

    I've done the same thing with a piece of newspaper under tungsten light. The in-focus parts are less sharp without the filter than with it.

    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 continue using the filters most of the time.

    --Peter
    i'm not doubting that Ir contributes to a lack of contrast/focus, but I'm stickin to my explanation here for this example.

    but I like the three bulbs reflected in your eye.

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    Senior Member Peter Klein's Avatar
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    Re: How IR filters affect M8 B&W

    Quote Originally Posted by Daniel View Post
    Peter,

    would you describe what you mean by IR smear?

    Dan

    When you take a picture without the IR filter, the IR component is not in focus where the visible light compenent is, causing loss of sharpness and contrast--it looks like a slight smearing effect at higher magnifications.

    --Peter

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