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Stella, again

Infrared
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#1 enricosavazzi

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Posted 14 May 2017 - 07:08

Slow weekends here, the spring is just starting, so not much to do outdoors. We had a little snow falling during the last week.
As Stella has been visiting, here are the latest updates.

Before the first haircut. I used two 60W tungsten bulbs for focusing and framing with an 850 nm low-pass filter on the lens, and an unmodified battery-operated strobe in TTL mode to expose this picture. Note the rather small pupils, caused by the incandescent lighting. Note also the triple reflection in one eye (flash and two lamps).
Attached Image: P3260095s.JPG

After the haircut. Now we can see that there had always been a dog hiding under all that fur, not an ewok. Here I used an 850 nm LED torch for framing and focusing, which did not cause the pupils to contract, and flash for exposing.
Attached Image: P4170064s.JPG

Here I used only the LED torch for exposure, which worked just fine. Pupils contracted because of an increase in ambient illumination (sun came out from behind a cloud). The torch itself produces no response in pupil size, so Stella is apparently not seeing in NIR. Note also the reflection of the torch in one eye. It appears to be a reflection from the retina or crystalline, not the cornea, because it is partly cut off by the edge of the iris.
Attached Image: P4170074s.JPG
-- Enrico Savazzi

#2 Andrea B.

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Posted 14 May 2017 - 19:28

I love the first photo. It is so charming!
In the last one it appears that Stella is saying "OK, that's enough!". :lol:

Do the light/dark tones of the fur change in IR from the Visible look??

Enrico, I know you would not use the 850 nm IR torch if it were not safe. Do you know if there is a value beyond which we should not use IR torches on living subjects?
Andrea G. Blum
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#3 enricosavazzi

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Posted 15 May 2017 - 05:40

View PostAndrea B., on 14 May 2017 - 19:28, said:

I love the first photo. It is so charming!
In the last one it appears that Stella is saying "OK, that's enough!". :lol:

Do the light/dark tones of the fur change in IR from the Visible look??

Enrico, I know you would not use the 850 nm IR torch if it were not safe. Do you know if there is a value beyond which we should not use IR torches on living subjects?
I don't know any quantitative limits, but from what I have read the only apparent damage that can be done by NIR is through thermal conversion. The eyes are of course most sensitive, but since we are talking about a continuous source, there is no flash heating at the power ratings available to us, and any discomfort would cause us/the subject to close the eyes or turn the head away. This probably means that we should be safe even from a NIR LED source of a few tens of W at close range. After all, tungsten lamps emit more than half their energy in the NIR, and no vision degradation has been reported for long-term tungsten illumination.

Stella is now mostly light gray with a white face (she was born completely black except a thin white ring around the muzzle), but the longest hairs (e.g. on the ears) are still black. So the tones are pretty much the same as in VIS. The lower lip and eyelids are instead black in VIS, but rendered as whitish in NIR. In NIR it is also easier to see through thin fur (e.g. around the nose) to the skin underneath, which makes Stella look very puppy-like.

*****

Editor: Thank you for your response about NIR. :)
-- Enrico Savazzi