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UltravioletPhotography

IR Filter Test with white balance at various wavelengths


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I have a bunch of IR filters ranging from 500nm to 900nm, they are made not for photography but lasers. Today I tested most of them on my Sony A7S. The lens I used was a 28mm f3.5 taken out from Nikon AF600, a film camera, I tested it in UV and it was not too bad, just half a stop slower than EL-Nikkor 85/5.6 at same aperture. The comparison is made with the help of another f3.5 lens, because this lens has no aperture to stop down. And when full open, it is soft in the edges.

 

With a same in-camera white balance, the photos look like this when put together:

 

 

With white balance applied in post:

 

 

White balanced with red-blue channels swapped:

 

 

I have noticed IR response differ significantly across cameras, when I was using Nikon cameras, I never got such purple color in trees with 500nm filter, also 700nm had more colors on Nikon if I remember correctly.

 

I also have two more filters which trasmit IR with a bit of light near 400nm

ZWB3:

This one does not pass through any visible light, however the long wave UV that is let through makes the sky blue, even without swapping the channels. It gives blue sky and blue foliage different from any other IR filters.

 

 

ZB1:

This filter appears as dark purple/blue in color, it transmits too much the visible spectrum so that the characteristic high contrast around the clouds is lost.

 

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Very nice display, Bruce. Thank you.

 

I have noticed IR response differ significantly across cameras

Does this difference you have seen coorelate with whether the camera has been modified or not?

 

Editor's Note: Bruce, I am going to edit your title to make it more searchable by indicating that it is an IR filter test.

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Andy Perrin
Interesting test. By 930nm, there should not be any hue variation left, so what you have there must be entirely from the white balancing? What happens if you do your white balance in post on the 930nm and then apply it to the others?
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We should all make our own version of this! It's so cool.
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Very nice display, Bruce. Thank you.

 

I have noticed IR response differ significantly across cameras

Does this difference you have seen coorelate with whether the camera has been modified or not?

 

Editor's Note: Bruce, I am going to edit your title to make it more searchable by indicating that it is an IR filter test.

Of course, Andrea, I'm talking about cameras with both IR filter and AA filter removed, only this way is the camera's sensor fully exposed to all wavelengths. There has been some success using unmodified camera for IR is the past, but today's newer camera always have strong IR filtration.
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Interesting test. By 930nm, there should not be any hue variation left, so what you have there must be entirely from the white balancing? What happens if you do your white balance in post on the 930nm and then apply it to the others?

In fact I did white balancing in post manually, that's how difference of hue is created in the 930 shot I guess. Actually using auto white balance in capture one always yield monochrome pictures from 800nm onwards.
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The 930 frame may still have a cast gradient, even if there is no true chromaticity. Careful Levels work could get rid of this, leaving a pure monochrome image. (Or take the lazy way out and convert to greyscale!)
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Andy Perrin

The 930 frame may still have a cast gradient, even if there is no true chromaticity. Careful Levels work could get rid of this, leaving a pure monochrome image. (Or take the lazy way out and convert to greyscale!)

Yes, that's what I'm talking about - since we know there isn't any chromaticity, it must be a cast. So why not white balance on the 930 frame and see what all the others do when you use that WB on them? I tried redoing it myself but the JPEG won't re-white balance properly.

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Andy Perrin

Shots taken at bright sunny days with filter at 800+ nm could be processed as from sensor without Bayer filter:

http://www.fpl.cz/tst/830nm_bayer.jpg

Yes, this is the improvement in resolution (from using the subpixels as if they are separate pixels) that I was discussing with Andrea way back here:

http://www.ultraviol...dpost__p__14343

 

We were not able to make it work at that time, but it seems someone has!

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