Archived posting to the Leica Users Group, 2006/11/15
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Leonard, I didn't notice any light loss with the IR cut filter (the Tiffen hot-mirror filter). These filters are listed in the manufacturers catalogs as having a filter factor of 1. Mark >From: Leonard Taupier <len-1@comcast.net> >Reply-To: Leica Users Group <lug@leica-users.org> >To: Leica Users Group <lug@leica-users.org> >Subject: Re: [Leica] Some IR filtration experiments >Date: Wed, 15 Nov 2006 16:25:37 -0500 > >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 > > >_______________________________________________ >Leica Users Group. >See http://leica-users.org/mailman/listinfo/lug for more information