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Not sure I understand. Aren’t human pupils black also because light goes in and doesn’t come back out?

hmottestad 2y ago
Would be interesting to know if dragonflies get red eyes when you take a picture of them with flash. Human eyes reflect some of the red light from the white flash, making it look like the pupil is red instead of black.
- seszett 2y ago
  I guess you're being downvoted because people think this is obvious, but dragonflies won't get red eyes because they don't have red blood to reflect the light. Red eyes are also caused by a particularity of vertebrate eyes, which have their blood supply in front of the retina. This is also the reason why you can sometimes see moving dots when looking at a bright, blue-coloured thing like the sky: your eye sees the whole capillaries filled with red blood cells, but the brain processes them out because they're always there. The large white blood cells then appear as "less red" dots in the processed-out streams of red, and the brain interprets them as bright dots. Insects have none of this, they don't have blood or blood vessels but a transparent haemolymph that doesn't really circulate through a complete circulatory system like us. So there really is nothing in front of the insects' light sensors to reflect light.
- wingspar 2y ago
  Went camping recently, and used one of those head mounted flashlights. Walking around there were glowing spots in the grasses. Thought at first it was some sort of firefly. Upon inspection, it was the light reflecting off the eyes of spiders. Dozens and dozens of spiders everywhere in the grasses. Never could get a picture. So light does reflect from compound eyes, but in ‘silver’.
deleted 2y ago
[deleted]
daemonologist 2y ago
The interesting bit (to me) isn't so much that they're black, but that you can see the compound eye at work. Each lens has a very narrow field of view and only appears black when the observer is within it, while a human pupil appears black from pretty much any angle because it's always using the one lens and aperture.
boxed 2y ago
Human eyes are a lot bigger. It's much easier to have a shadow in a thing that is a few centimeters big, than it is in something half a millimeter deep.
- DonHopkins 2y ago
  [flagged]
  - boxed 2y ago
    Is slander not a thing where you live? It is here... No, I didn't actually say that. But I tried to point out that lying and screaming insults is bad. Which you counter by lying and screaming insults...
  - hombre_fatal 2y ago
    Come on. We can't be rehashing prior engagements we've had with other HN users every time they rear their head. Especially not when they comment on the shadows in a bug's eye columns.
  - itishappy 2y ago
    Why is this relevant or useful here?

Would be interesting to know if dragonflies get red eyes when you take a picture of them with flash. Human eyes reflect some of the red light from the white flash, making it look like the pupil is red instead of black.

seszett 2y ago
I guess you're being downvoted because people think this is obvious, but dragonflies won't get red eyes because they don't have red blood to reflect the light. Red eyes are also caused by a particularity of vertebrate eyes, which have their blood supply in front of the retina. This is also the reason why you can sometimes see moving dots when looking at a bright, blue-coloured thing like the sky: your eye sees the whole capillaries filled with red blood cells, but the brain processes them out because they're always there. The large white blood cells then appear as "less red" dots in the processed-out streams of red, and the brain interprets them as bright dots. Insects have none of this, they don't have blood or blood vessels but a transparent haemolymph that doesn't really circulate through a complete circulatory system like us. So there really is nothing in front of the insects' light sensors to reflect light.
wingspar 2y ago
Went camping recently, and used one of those head mounted flashlights. Walking around there were glowing spots in the grasses. Thought at first it was some sort of firefly. Upon inspection, it was the light reflecting off the eyes of spiders. Dozens and dozens of spiders everywhere in the grasses. Never could get a picture. So light does reflect from compound eyes, but in ‘silver’.

deleted 2y ago

[deleted]

daemonologist 2y ago

The interesting bit (to me) isn't so much that they're black, but that you can see the compound eye at work. Each lens has a very narrow field of view and only appears black when the observer is within it, while a human pupil appears black from pretty much any angle because it's always using the one lens and aperture.

boxed 2y ago

Human eyes are a lot bigger. It's much easier to have a shadow in a thing that is a few centimeters big, than it is in something half a millimeter deep.

DonHopkins 2y ago
[flagged]
- boxed 2y ago
  Is slander not a thing where you live? It is here... No, I didn't actually say that. But I tried to point out that lying and screaming insults is bad. Which you counter by lying and screaming insults...
- hombre_fatal 2y ago
  Come on. We can't be rehashing prior engagements we've had with other HN users every time they rear their head. Especially not when they comment on the shadows in a bug's eye columns.
- itishappy 2y ago
  Why is this relevant or useful here?