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[IR] Are your eyes sensitive to IR?

Jerome Marot

Well-known member
I have been experimenting with IR last week-end. I use a modified digital camera, of which I removed the IR block filter and an Heliopan RG 780 IR filter. That particular filter has a maximum at 780 nm and cuts all the visible under 700 nm.

With this setting, I can take typical B&W IR pictures after some post-processing:


The filter is mounted in an adapter which ends in an open cylinder and I had the curiosity to look through the filter with my naked eyes. It takes some effort to make sure the cylinder is well fitted and that you do not get light leaks. Then, at first it is dark until my eyes get accustomed. After a few seconds, I see this:


(It is the same image with different post processing, to make it appear red. I see everything red through the filter, obviously.)

I was surprised but I checked the relevant literature. Apparently, it is not uncommon that the human eye has some residual sensitivity to IR light which normally goes unnoticed because of the much higher sensitivity to visible light.

Try it, you may also be surprised!

A word of caution: do not directly look at the sun through the filter, for blindingly obvious reasons.
 
I regularly preview the effect through my IR680 and IR720 filters before I expose film. It takes about 30 seconds of dark-adaption with no big light leaks around the edge of the filter for the IR landscape to pop into view. There are limitations to how dark a scene one can preview; broad daylight works well, deep shade fails for me.

Jerome Marot is right to caution against looking at the sun. The dark-adapted eye is defenceless. It has a wide open iris so even a momentary glimpse of the sun-disk is bad. And it is the IR rays in particular that burn the retina!
 

Jerome Marot

Well-known member
I regularly preview the effect through my IR680 and IR720 filters before I expose film. It takes about 30 seconds of dark-adaption with no big light leaks around the edge of the filter for the IR landscape to pop into view. There are limitations to how dark a scene one can preview; broad daylight works well, deep shade fails for me.

I let other people try the filter, and there is quite an amount of difference between people. I take less than 10 seconds to adapt, my wife needs a much longer time and can only vaguely see what I see rather clearly. A friend of mine who worked in an optical firm using high power IR lasers did a few experiments some years ago and confirmed that IR sensitivity varies a lot between people.
 

Dr Klaus Schmitt

Well-known member
I have gathered info about UV and IR vision a while ago, so here is a result of the sensitivity of our three cones over wavelength. As you see, it does not stop at 700nm nor 400nm (the usual set limits). So depending on intensity, we're able to see a bit of UV as well as IR. Both works for me, too btw.

spectrum3.jpg

(c) maxmax.com

Here is an interesting Link about tests for human IR vision wearing IR Goggles claiming the following IR sensitivity of the human eye:

leefltr4.gif


and that older (1947) IR sensitivity study which shows, that it is just a matter of intensitiy times sensitivity that we humans see IT

IRcurve_HVS.jpg

(c) Griffin, Hubbard, & Wald, J.

Another interesting graph showing the overall sensitivity of the human eye ("Human is a hidden tetrachromat")

tetracomp.gif

(c) neuronresearch

A highly recommend source btw. http://www.neuronresearch.net/vision/
 

Vivek Iyer

New member
It is an interesting topic. I have natural residual UV and IR sensitivity.

While eyes start to fluoresce in near UV, making everything looking "foggy", near IR does not trouble my eyes much.

Near IR even makes a splendid tool to photograph the eye in a non intrusive manner.



Untitled by Vivek Iyer, on Flickr​
 

Dr Klaus Schmitt

Well-known member
That's an excellent shot Vivek! Never seen before such one.

I think many people have some UV and IR sensitivity, yet they
simply don't know about. I discovered that myself when I looked
into the output of a monochromator once.
 
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