fotoism Posted February 5, 2009 Share #1 Posted February 5, 2009 Advertisement (gone after registration) I recently acquired a Canon hot mirror filter from the bay and the seller described it as "uv/ir cut" although the filter itself says "hot mirror". When trying it on some black fabric I noticed a reduction of the magenta cast to a darker shade, but not quite back to black. My other UV/IR cut filters ( Leica, Heliopan, and B+W ) are all able to correct the color to black under the same setting. Are "UV/IR cut" and "hot mirror" two different beasts? Phil Link to post Share on other sites More sharing options...
Advertisement Posted February 5, 2009 Posted February 5, 2009 Hi fotoism, Take a look here UV/IR cut vs. hot mirror. I'm sure you'll find what you were looking for!
ArtZ Posted February 5, 2009 Share #2 Posted February 5, 2009 Phil, IR filters are also called "Hot Mirror filters". Link to post Share on other sites More sharing options...
fotoism Posted February 5, 2009 Author Share #3 Posted February 5, 2009 Thanks Artz. That's what I thought, too. But why is this Canon filter unable to correct the magenta cast like the others? Are there different grades of IR cut filters in terms of corrcting ability? Is there any way I can make it behave like the others? Phil Link to post Share on other sites More sharing options...
ArtZ Posted February 5, 2009 Share #4 Posted February 5, 2009 Thanks Artz. That's what I thought, too. But why is this Canon filter unable to correct the magenta cast like the others? Are there different grades of IR cut filters in terms of corrcting ability? Is there any way I can make it behave like the others? Phil I think it's because of the formula. The Canon Hot Mirror filter is probably weaker than IR cut filters for Leica M8. Remember: Canon sensors have already an IR cut filter built-in! With wide Leica lenses (Tri-Elmar 16-18-21 in particular) you get better results with Leica brand IR filters than B+W... because of the formula. Even the 67mm Leica IR filter for the WATE has a different formula than other Leica IR filters. Link to post Share on other sites More sharing options...
fotoism Posted February 5, 2009 Author Share #5 Posted February 5, 2009 Hmmm. Internal filter - that explains. Thanks. Phil Link to post Share on other sites More sharing options...
thai.charlie Posted February 5, 2009 Share #6 Posted February 5, 2009 i've got tiffen hot mirror filters left over from the days of the Nikon NC2000 DSLR digital news camera (its Canon counterpart was the DCS-3, I'm guessing that's where these are from) and I use them with step up rings on some of my lenses on my M8. The IR correction is not as strong as the current 486 and Leica IR cut filters, but it helps a little. Subsequent DSLR camera was the Kodak DCS520/Canon D2000 which had a built in IR cut filter behind the lens, so these filters would have not been necessary. Link to post Share on other sites More sharing options...
scott kirkpatrick Posted February 5, 2009 Share #7 Posted February 5, 2009 Advertisement (gone after registration) "IR cut" and "hot mirror" seem to be used to mean the same thing -- decreasing IR that would get to the sensor. But there are many ways to do this, and saying one is "weaker" or "stronger" doesn't characterize the differences. If it is a dichroic (interference) filter, the filter characteristic (absorption percentage as a function of light wavelength) rises sharply from no absorption at visible wavelengths to near 100% absorption at some cutoff wavelength, but different filters cut off at slightly different wavelengths. If the filter relies on absorption by a dye, the rise in absorption will occur more gradually, over a wider range of wavelengths. In order to be effective in suppressing IR, this kind of filter has to suppress some nearby visible wavelengths, causing more of an overall green cast. Leica/Kodak chose the latter kind of filter as the cover glass for the sensor in the M8, perhaps to avoid internal reflections. In specifying the dichroic filters that go in front of the lens, they eventually settled on a formulation that cuts off slightly deeper into the IR than the B&W 486. When this was a hot forum topic, one poster proposed to get out a spectrophotometer and actually measure the characteristics of the different filters available for suppressing IR, from Schneider (B&W), Hoya and Tiffen, but I never saw the final results of that very interesting piece of research. Since the effect in images depends strongly on the character of the light, it's hard to judge from anecdotal examples. scott Link to post Share on other sites More sharing options...
ho_co Posted February 6, 2009 Share #8 Posted February 6, 2009 Scott, nice job! Succinct summary of all those dreary pages of yore! First-rate. Link to post Share on other sites More sharing options...
andit Posted February 6, 2009 Share #9 Posted February 6, 2009 Hi Guys, This might be a stupid question, but don't you think that it is possible for Leica to be incorporating the IR Cut into the coatings of the lens elements of all new lenses. That is to say that as from serial number xxxxxxx you no longer need the IR Cut Filter. This seems to make sense to me and reduces the number of air to glass surfaces, introduced by the filter, that can cause flare and reflections. Andreas Link to post Share on other sites More sharing options...
ho_co Posted February 6, 2009 Share #10 Posted February 6, 2009 Andreas, no, I don't think so. For an interference filter to work, I think is has to be on a plane surface. Leica could, of course, make the first piece of glass plane and give it the interference coatings, but that would then require that people shooting film go through some kind of electronic manipulation to remove the cyan drift that the filtered lenses would produce. I think as long as Leica is producing for film and digital, the filter can't be in the lens. (Might be an exception for lenses 50mm and longer, though. Certainly an interesting idea.) Link to post Share on other sites More sharing options...
andit Posted February 6, 2009 Share #11 Posted February 6, 2009 Hi Howard, Thanks for the info. Your explanation makes sense - they could put it into the cement that bonds lens halves together. I'm pretty sure that those are plane surfaces. Andreas Link to post Share on other sites More sharing options...
lars_bergquist Posted February 6, 2009 Share #12 Posted February 6, 2009 Hi Howard, Thanks for the info. Your explanation makes sense - they could put it into the cement that bonds lens halves together. I'm pretty sure that those are plane surfaces. Andreas Certainly not. Most of them are spherical, as can be seen from the lens diagrams that Leica publish. The old man from The Age of Max Berek Link to post Share on other sites More sharing options...
stunsworth Posted February 6, 2009 Share #13 Posted February 6, 2009 Thanks for the info. Your explanation makes sense - they could put it into the cement that bonds lens halves together. I'm pretty sure that those are plane surfaces. Yes, but then the wider lenses would be useless for colour film work. Link to post Share on other sites More sharing options...
tgray Posted February 6, 2009 Share #14 Posted February 6, 2009 When this was a hot forum topic, one poster proposed to get out a spectrophotometer and actually measure the characteristics of the different filters available for suppressing IR, from Schneider (B&W), Hoya and Tiffen, but I never saw the final results of that very interesting piece of research. Since the effect in images depends strongly on the character of the light, it's hard to judge from anecdotal examples. scott I could do that at work with one of our spectrometers. Might be interesting. However, since I don't have an M8, I don't have any IR cut filters... Haha. Link to post Share on other sites More sharing options...
scott kirkpatrick Posted February 6, 2009 Share #15 Posted February 6, 2009 If you are serious, I think a loan of samples could be arranged. I have Leica and B&W. Does anyone want to contribute Hoya or Tiffen specimens? scott Link to post Share on other sites More sharing options...
tgray Posted February 6, 2009 Share #16 Posted February 6, 2009 Sure. The one caveat to this is that I don't have a uniform broadband light source. Not the end of the world, but near the UV things might get a little dicey. Regular tungsten lamps are fine for the red end of things. Link to post Share on other sites More sharing options...
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