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07-17-2012, 07:08 AM   #31
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QuoteOriginally posted by slackercruster Quote
I checked the WB. It was set to auto. Should I be using a custom WB for IR?
Shooting RAW with these 6MP cameras in IR is critical, especially because the white balance isn't going to be perfect. You have much more latitude with the pictures in RAW than from JPEGs. Even though I convert to black & white, you can still recover more details by changing white balance in RAW. (You have to play around with it to get it right.)

I looked up your Sigma 8-16 on Photozone and it looks reasonably sharp. There is heavy vignetting wide open, so make sure that you are shooting in Av mode (or M mode) and stopping down to f/8 or f/11.

I would try my focus bracketing method, making sure that you're stopped down with that Sigma, and shooting in RAW. Then report back if it worked!

07-17-2012, 07:43 AM   #32
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QuoteOriginally posted by Asha Quote
I don't actually know how far into the IR the Pentax sensor sensitivity is. I just want to add a caution that people emit heat, which is basically what IR is. So, the mixing of reflected visible light with the emitted IR light from people's bodies will definitely not look as sharp as a "normal" visible spectrum photo.
QuoteOriginally posted by Asha Quote
Good point, and there are actually a couple things to consider.

"Ghosting", would be present for both IR and visible if the design is prone to it. Ghosting is when reflected light inside an optical system converges, forming a ghosted spot of light. This would occur from light coming into the system from the scene being photographed. So, if you have visible light ghosting in a lens, you'll most likely get IR ghosting too. Since IR conversion involves removing a filter from the detector, then you have effectively altered the design, and you might get ghosting that wasn't present before the conversion.

Also, when the detector runs continuously and when you use the LCD a lot, heat builds up around the detector. Since the converted camera is more sensitive to IR, this heat will cause fogging inside the camera cavity. This would not likely cause ghosting since rays are not directed and are bouncing around in all directions, but it would definitely cause a reduction in contrast and likely lower the sharpness too. Plus, the sensor noise increases, which compounds the problem.
All this technical discourse is one thing... but have you ever shot digital infrared photography before at all? Because what you're writing about is pure bunkum and reflects a flawed understanding of what IR photography is all about (and there is definitely a difference between shooting IR film and digital IR photography). IR is not merely about heat emitted. It is possible to shoot people as sharp at IR wavelengths as at normal visible spectrum, and here two IR images to prove it.


Last edited by creampuff; 07-17-2012 at 07:59 AM.
07-17-2012, 08:08 AM   #33
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QuoteOriginally posted by carpents Quote
Shooting RAW with these 6MP cameras in IR is critical, especially because the white balance isn't going to be perfect. You have much more latitude with the pictures in RAW than from JPEGs. Even though I convert to black & white, you can still recover more details by changing white balance in RAW. (You have to play around with it to get it right.)

I looked up your Sigma 8-16 on Photozone and it looks reasonably sharp. There is heavy vignetting wide open, so make sure that you are shooting in Av mode (or M mode) and stopping down to f/8 or f/11.

I would try my focus bracketing method, making sure that you're stopped down with that Sigma, and shooting in RAW. Then report back if it worked!

Thanks!
07-17-2012, 08:11 AM   #34
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QuoteOriginally posted by creampuff Quote
All this technical discourse is one thing... but have you ever shot digital infrared photography before at all? Because what you're writing about is pure bunkum and reflects a flawed understanding of what IR photography is all about (and there is definitely a difference between shooting IR film and digital IR photography). IR is not merely about heat emitted. It is possible to shoot people as sharp at IR wavelengths as at normal visible spectrum, and here two IR images to prove it.

They are OK, but I would not say they are as sharp as reg non IR pix. At least not what I call sharp. But for IR...they seem OK and I would not complain. (much)

07-17-2012, 08:52 AM   #35
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Much of the wide ranging IR discussion above has some truth to it but has little to do with the problem presented here.

In this case the lack of sharpness lies primarily in the hazy light that came through the red Bayer filter. This is unequivocally shown by the color separated image's "red" channel - according to the histogram of that channel there is NO black anywhere in the image - clearly not true. The reason it looks this way is a haze about 1/3 maximum brightness is smeared over the whole scene.

Is this a problem in all (or many of) your un-sharp images? It would be wise to find out I think. Is it as severe for all your lenses?

It might be wise to manually set white balance by shooting off grass or tree foliage.

Keep in mind that "white balance" is up to you for IR photography - convention has it that tree foliage is white for IR photos - that means R, G, & B channel gains should be adjusted to give white when looking at whatever it is that you want to be displayed as white.

I think a bit or experimentation or review of photos you've already taken will identify if the red channel haze is always present (inherent in your camera's IR filter), dependent on scene lighting (time of day), or white balance, or dependent on lens choice. Once that is identified the solution may be obvious.

Dave in Iowa
07-17-2012, 05:01 PM   #36
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I think there's a reasonable chance your IR conversion filter is letting in too much red light (below about 720-750nm.) The trees are just not bright enough.

Here's an IR test I shot a long time ago comparing a Wratten 25A (580nm-used for film IR) filter with a Hoya 72 (720nm) filter; note the difference in tree brightness between the two filters. This is why I suspect there's too much visible red light in your photo.


An easy way to see if this is indeed the case is to mount an external IR filter with a 750nm or so cut-off. It may fix the problem and have just a small effect on exposure times.

Dave in Iowa

Last edited by newarts; 07-17-2012 at 05:15 PM.
07-17-2012, 08:13 PM   #37
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Well, creampuff, I now I know what side of the physics and engineering line you stand on. Thanks for the clarification.
07-18-2012, 08:13 PM   #38
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I plan on doing some tripod tests with various lenses. I hope to get out next week to shot the IR. Will send in all the pix when done.

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