Out of Spectrum Photography

Last year I got intrigued by IR photos found somewhere on the Internet. After a further investigation, I decided to try it out by myself. I bought ZWB2 filter, which basically blocks all visible light, while passing most of UV and IR.

Filter's transfer functions
 
 
I took a few photos but the results were terrible. In order to get any but pure black image I had to use a strong UV source and a few second exposure time, otherwise the image was pure black.
photo with filter, 3s exposure

photo without filter, 1/60s exposure

The results were promising but where this huge time difference come from? One possible explanation would suggest that the
camera is over 200 times less sensitive to UV than to the normal light (including blue
nearby).

Answer to this is as follows:

  • filter at its peak transmits 80% of UV light
  • lenses have many glass parts and glass stops UV (later I found that anti-reflective coatings make it even worse)
  • sensor itself contains exactly opposite filter, which cuts out IR and UV

After discovering this I felt proud that my filter is more powerful than CANON's one. Fan stopped (since I found out that my friend used high power UV sources to take photos and I didn't feel special anymore). Until a few months ago when my family decided to upgrade an old camera to brand new D5 mark II. I kept the old camera (as it can be bought for far less than 100$ so it's worth even less) and send it to a magician to remove a filter on a sensor. A problem appeared because I also lost an antialiasing
filter and an optical path changed its length, but only for the sensor. By that, photos of dense lines (rooftops, fences, etc) looked more like they were taken from phone than a quality camera. What's worse autofocus got offset from an ideal value. On the other hand I was now able to reduce an exposure time by significant amount, almost 2 orders of magnitude, up to the point that I could go outside and take pictures by hand using sunlight only. 



extended spectrum photos (visible + NIR)

Photos of same place from 3 different spectra:




 

And at the end I prepared a quiz. Can you figure out in what color/wavelength each of this photos was taken?








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