[Leica] Some IR filtration experiments

[len-1 at comcast.net (Leonard Taupier)]

Mark,

Great work. Your results are especially interesting to me as I want  
the kind of sensitivity to IR that the M8 has. I shoot a lot of IR  
photos. That's just the opposite of everybody else. I'm very familiar  
with the IR sensitivity of the D200 (none), the D2H (little more than  
average), D2X (a little less than the D2H), and D1X ( more sensitive  
than the D2H). The hot mirror IR filter approach may be fine in the  
short term but that's slowing down all your lenses by 1 to 2 stops.  
Since your experiment with the Phase One profile has only limited  
success, you're right. Leica will have to fix it. That may not be too  
easy as Leica has already suggested that adding an IR filter over the  
sensor may (my interpretation) mess up their edge performance they  
went so hard to develop). Your new Heliopan filter experiment will be  
interesting but I think the UV contribution to the problem is very  
minor compared to IR. Most modern lenses roll off UV fairly well.  I  
have to use enlarging lenses for UV images. And your D200 also has  
absolutely no sensitivity to UV. It looks like a winner right now.  
While I want the IR sensitivity of the M8, not at the expense of  
color cast problems. For now I'll just wait and see how the M8  
evolves and continue to buy more film for my M6 and M7s.

Thanks and keep us informed on your future experiments.
Len


On Nov 15, 2006, at 1:45 PM, MARK DAVISON 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
>
>
>
> _______________________________________________
> Leica Users Group.
> See http://leica-users.org/mailman/listinfo/lug for more information