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Old Feb 17, 2016, 1:32 PM   #21
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John, I think you may be overly complicating this. If you remove the IR blocking filter, and the Bayer filter, then place the IR pass filter in front of the lens, the only thing the pixels on the sensor will see is IR levels.
If you leave the Bayer filter in place, it will block some of the IR to those pixels which are under the blue (the most), green (partly), and red (least) parts of the filter. If you view this as a color image, it would show up with a strong red cast, as that is where most of the light is. If you remove the Bayer filter, all pixels will get the same illumination (assuming you're aiming at a blank wall), but if you view this as a color image, it will tend to look blue because of how the camera software interprets the pixel values. It is because the Bayer filter has twice as many green pixels as red or blue, so those pixels have to be given greater weight when mixing colors. Since the sensor itself is more sensitive to red light than blue, the blue pixels get a bit more weight than the red. Switching your camera to monochrome will be more correct.
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Old Feb 18, 2016, 10:06 AM   #22
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Hi Conor,
Yes, I understand. It's just the term 'unexposed' I find odd. How can one unexpose what hasn't been exposed. Never mind, I'm just being anal.
.... john
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Old Feb 18, 2016, 10:41 AM   #23
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Hi VTphotog/Tcav,
Right, OK. That makes it quite clear. I think that Tcav was trying to tell me the same thing, but I just didn't get it.
So, where is the Bayer filter, and is it easily removed?
I finally received the film, from the film club. (They're in California. It's VERY good of them to do this for me.) They sent me three strips, a very dark and a very light (kind of orangish/brown). I'm assuming that these are exposed and unexposed, respectively. The exposed seems to remove all colour from the IR/colour image. The unexposed doesn't seem to remove much. Most the the write ups say to use 2 or 3 layers, so I may try this. The images produced are heavily red/blue(?) Have a look here
I believe that I can remove this cast by doing a RGB switcharoo.
Tcav. Yes, getting the proper filter would be the easiest (and probably best) way, but what fun would there be in that.
Just a side note. Removing the IR block filter has left me with a camera that can be used for both visible and infrared, after some minor processing. This flexibility is interesting. If I remove the Bayer filter now, I loose the option of taking colour.
..... john
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Old Feb 18, 2016, 11:49 AM   #24
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You've got a camera without an IR Blocking filter. Any photos you take will be tinted red depending on the amount of IR in the scene, because the IR won't pass through the blue and green microfilters in the Bayer Filter, but will pass through the red microfilters, so the camera will think the IR is red.

If you install an IR Blocking filter, like a B+W 486, you can capture conventional color photos without the red tint from any IR.

If you install an IR Passing filter instead, like a B+W 093, you can capture IR photos where the IR will appear as red.

Anything else, and there's no way to know what you'll be capturing.
  • The lens is the thing.
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Last edited by TCav; Feb 18, 2016 at 11:51 AM.
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Old Feb 19, 2016, 10:23 AM   #25
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Hi Tcav,
Alright. Sounds good. I'll look into it.
... john
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