[Leica] Some IR filtration experiments

[msadat at gmail.com (mehrdad)]

my suspicion is that the m8 has to go in for a fix and probably only
solms can fix it. i think with the hot filter you can delay the "fix"
for a while. for me at least till after Christmas


On 11/15/06, MARK DAVISON <davison_m@msn.com> wrote:
> I have been conducting some experiments to understand the issue of IR
> contamination and filtration in digital cameras.  I have posted some 
> results
> at
>
> http://gallery.leica-users.org/v/MarkEDavison/M8infrared/
>
> to show some comparative examples of IR filtration.  I have included a 
> Leica
> M8 shot where the filtration was done by applying a modified Phase One
> profile which is supposed to correct blacks under tungsten light. My
> conclusion is that the software filtration works surprising well on the
> blacks that are IR contaminated, but hardly affects the other contaminated
> colors at all, but you should look and come to your own conclusion.
>
> (Note: this is a cross post.  There is an on-going discussion of software
> profile methods for IR filtration at
> http://www.leica-camera-user.com/digital-forum/9178-magenta-work-around-capture-one-workflow.html
>
> or
>
> http://tinyurl.com/y6cjx2
>
> which gives more detail on the origins of the modified profile I used on 
> the
> Leica M8 image.)
>
> Here's a description of the shots:
>
> The scene was shot with incandescent illumination from ordinary lightbulbs.
> The camera white balances were set to 2800 K  except for the Epson R-D1,
> which was set to incandescent. (The Epson R-D1 does not allow you to set
> white balance in Kelvin.)
>
> The first example is the D200, which is very insensitive to IR. The colors
> in the first D200 photograph are a very accurate rendition of the way the
> scene appears to my eye. Take special note of the maroon and green pile
> blankets, the black Leica M lens, and the black pile jacket at the bottom 
> of
> the photograph. The second photograph shows the D200 with IR cut filtration
> (via a Tiffen standard hot mirror filter). There is hardly any visible
> change in the colors. The third photograph is with the D200 and the IR pass
> filter (a Hoya R72), taken at the same exposure as the first two
> photographs. There is no visble IR at all at this exposure.
>
> The photographs continue in sequence for 3 more cameras: the Leica M8, the
> Epson R-D1 and the Nikon D2h. For each camera I show an image with no
> filtration, with IR cut, and IR pass, all at the same exposure. Note how
> much IR is recorded by the M8--it is the most IR sensitive of all the
> cameras. Note also how the IR contamination has completely bleached the
> green out of the green pile blanket, how the maroon blanket has shifted
> color, how there is a purple sheen on the barrel of the Leica lens, and how
> the black pile jacket has turned dark purple. The shot with IR cut
> filtration knocks down the purple sheen on the lens barrel, improves color
> saturation and contrast overall, but doesn't quite return the green pile
> blanket to the correct color. Note also that there was a glowing IR
> reflection from the "black" pile jacket on the bottom of the apple which is
> taken out by the IR filtration.
>
> Similar comments apply to the Nikon D2h, but the infrared sensitivity is
> weaker and the corrections with the IR cut filter look better to my eye.
>
> The Leica M8 shot which has been filtered by application of the profile
> Jamie Roberts supplied does have better blacks in the anodized aluminum
> objects, but the green of the pile blanket at the top has not been 
> restored,
> and in general the colors of the pile fabrics look faded.  More subtly, the
> IR reflection on the bottom of the apple has not been removed.
>
> My point is that IR contamination doesn't just affect synthetic black
> objects and dark anodized aluminum--it contaminates practially all 
> synthetic
> pile fabrics that I can find in my house. So you can't just hunt down dark
> purple things and change their color. (By the way, if you shoot social
> events and students in classrooms in Seattle in the winter, you are going 
> to
> encounter a lot of pile jackets and incandescent light, so this is not some
> obscure rare combination, at least for my use.)
>
> The Tiffen hot mirror filter which I used in these experiments is obviously
> too weak to restore all the colors (especially for the green pile fabric),
> so I have a better UV/IR cut filter on order--a Heliopan 8152.
>
> Some philosophical notes:
>
> I have been using these other cameras for some time now, and I always had
> more trouble getting indoor shots from the R-D1 and D2h to look "right".
> There was some indescernible purpleness about these photographs that
> reminded me of faded advertising posters. In comparison the D200 
> photographs
> looked rich and vibrant.  Now I understand the source of the problem. I'll
> be using the IR cut filters on the other cameras when the situation
> warrants.  I have also noticed that foliage never looks right in the IR
> sensitive cameras--it's always a funny spring green.  I will wager anything
> that this comes from high IR reflections in plant leaves, even under
> daylight.
>
> One huge difference between a film and digital camera is that the spectral
> sensitivity functions of the digital camera R, G, and B channels are fixed
> forever.  You can't change the spectral sensitivities by simply loading a
> different brand or type of film. Since this is the case, I think it would
> make life easier for serious photographers if digital camera manufacturers
> would measure the spectral sensitivity functions of their cameras and
> publish them, just as Kodak does with their films.  With such a graph you
> can tell at a glance if the camera has significant IR or UV sensitivity, 
> and
> you can pick your lens filters accordingly.
>
>
>
>
>
>
> Mark Davison
>
>
>
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>


-- 
  -------------------------------------
  regards, mehrdad