Infra-red vision vs. dark vision...

[Anthony]

Originally Posted by whswhs

But it's not only pupil size. It's also how closely spaced the receptors can be. Human retinal neurons are as close together as is permitted by the wavelength of visible light. If you go to thermal infrared wavelengths you need the neurons to be more widely spaced.

Or you can average across multiple neurons. Realistically you'll need a separate set of eyes anyway since the optics are different and I'm pretty sure the vitreous humor is opaque to IR.

[whswhs]

Originally Posted by Ji ji

Or maybe the vitreous humor could be substituted by biological optical fibers bringing the light to a multilayer retina, multiplying the retinal surface by the number of layers.

I think if you did that you'd simply be replacing the issue of IR photons blurring across multiple retinal neurons with the issue of IR photons blurring across multiple optical fibers. At least, if you're planning to put the fibers into an eyeball of the same size. If you make the eyeball much bigger, you can avoid that problem, but then why wouldn't you just have more widely spaced retinal neurons?

[Anthony]

Originally Posted by whswhs

I think if you did that you'd simply be replacing the issue of IR photons blurring across multiple retinal neurons with the issue of IR photons blurring across multiple optical fibers.

Neither one matters much. It's useless to have neurons more tightly packed than the resolution of your lens, but it's not actively harmful.

[Ji ji]

Originally Posted by Anthony

Neither one matters much. It's useless to have neurons more tightly packed than the resolution of your lens, but it's not actively harmful.

the idea was about layering several retinas, so to multiply the surface in a sphere of same size. The same number of receptors could be spaced along more surface.

Originally Posted by whswhs

I think if you did that you'd simply be replacing the issue of IR photons blurring across multiple retinal neurons with the issue of IR photons blurring across multiple optical fibers. At least, if you're planning to put the fibers into an eyeball of the same size. If you make the eyeball much bigger, you can avoid that problem, but then why wouldn't you just have more widely spaced retinal neurons?

Maybe then we could use optic fibers to build an eye with larger volume (and possibly larger/multiple pupils) in a form factor less constrained than a sphere. While, at the same time, retaining normal eye mobility - unlike an owl.

[whswhs]

Originally Posted by Anthony

Neither one matters much. It's useless to have neurons more tightly packed than the resolution of your lens, but it's not actively harmful.

But I'm not concerned with "actively harmful." What I'm saying is that it doesn't matter how many neurons you have in an area, or how many biofibers, or how many cells of a compound eye, or whatever you want to imagine; your pixels still end up being as far apart as the wavelength of the radiation dictates, or farther (average mammal vision has poorer resolution than human, presumably because sharp eyesight is biologically expensive in some way).

Now I think of it, human night vision relies on somewhat widely spaced rods, and has poorer resolution than day vision. Thermal IR vision might be comparable. It would realistically not so much take away vision penalties for dim light as limit them to no more than, say, -4 no matter how dark it was, as long as you were looking at hot objects. Of course you'd have an enhanced ability to spot and target hot objects, which seems to be what snakes use it for.

I'm not sure it would be impossible for a homeotherm to have such a sense. I can feel the warmth of another human body that's no hotter than mine, or of a feline body that's maybe just slightly warmer; I can judge if a human being has a fever. You would have some problems with thermal noise, though; colder receptors for IR are more sensitive.

[Anthony]

Originally Posted by whswhs

It would realistically not so much take away vision penalties for dim light as limit them to no more than, say, -4 no matter how dark it was, as long as you were looking at hot objects.

I'm really not sure how much visual resolution should matter (not specific to IR). At a range of 6' (a typical actual distance between melee combatants) normal human vision has a peak resolution of 0.02", but even 0.2" is far smaller than any target you're going to be attacking. It makes more difference for depth perception, but you're still better off than someone with One Eye.

[Hide]

Well, I think you got a nice idea on this subject already. When I had to deal with this matter I took the example of Geckos. Then my approach was "porting" such eye attributes to a humanoid.

This was useful for me: "Gecko vision" & "Gecko vision 2".

So it might as well help you... "Gecko vision 2" provides you with a PDF that may give you another approach.

- Hide

[johndallman]

Originally Posted by whswhs

(average mammal vision has poorer resolution than human, presumably because sharp eyesight is biologically expensive in some way).

It's going to need more brain matter to process all the information. We also mount our eyes higher than most mammals, which helps keep dirt out of them, and lets us see further by seeing over many things. Long-range vision needs sharpness to get the best use out of it.

[whswhs]

Originally Posted by Anthony

I'm really not sure how much visual resolution should matter (not specific to IR). At a range of 6' (a typical actual distance between melee combatants) normal human vision has a peak resolution of 0.02", but even 0.2" is far smaller than any target you're going to be attacking. It makes more difference for depth perception, but you're still better off than someone with One Eye.

No, it's more of a problem for reading and for perceive facial expressions made with small muscles, which are also distinctive to primates and even more to humans.

[VonKatzen]

You can have semi-realistic pseudo-darkvision if your subject has active sensors - light emissions in the UV-spectrum gives better resolution than visible light. But it's pretty tricky to explain biologically.

As far as infravision sight problems it's not just that it's blurry, it's also a narrower spectrum (at least most of what we use in IR cameras is) so there's not as much differentiation by color.