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Help! Question about eyes and light angles
Posted: Wed Dec 11, 2019 11:53 am
by Fishnut
I have a question that I'm having trouble answering and would appreciate some help. I need to know what is the maximum angle that light can hit the pupil and still be seen by the eye.
So, in my crappy drawing below the green line can be easily seen, the orange line just seen and the red line can't be seen.
- eye.png (6.3 KiB) Viewed 7453 times
I need to know at what angle the light can no longer be seen, and how much it varies across species (I'm interested in fish but will take any vertebrate if need be).
Re: Help! Question about eyes and light angles
Posted: Wed Dec 11, 2019 12:56 pm
by El Pollo Diablo
Is this a different question to
visual field?
Re: Help! Question about eyes and light angles
Posted: Wed Dec 11, 2019 12:57 pm
by Gfamily
Fishnut wrote: Wed Dec 11, 2019 11:53 am
I have a question that I'm having trouble answering and would appreciate some help. I need to know what is the maximum angle that light can hit the pupil and still be seen by the eye.
So, in my crappy drawing below the green line can be easily seen, the orange line just seen and the red line can't be seen.
eye.png
I need to know at what angle the light can no longer be seen, and how much it varies across species (I'm interested in fish but will take any vertebrate if need be).
Does "it varies" help?
I've seen a diagram suggesting some waterfowl can see >180 from each eye, so they potentially get binocular vision both in front and behind their head.
Birds of prey are likely to have much narrower fields of view as that need a lot of acuity for locating and catching prey.
Can't say for fish, though I'm pretty sure that water/eye light rays would refract less than air/eye light rays would, so their fov would be typically smaller
Re: Help! Question about eyes and light angles
Posted: Wed Dec 11, 2019 12:58 pm
by Martin Y
Wikipedia's page on the visual field notes that human vision actually extends beyond 90° outwards.
https://en.wikipedia.org/wiki/Visual_field
PS duplicate of an already posted link because I was retyping my post on my phone as "Your IP <address> has been blocked because it is blacklisted ". I fondly imagined we had left that pain in the bum behind in the other place. Seems not.
Re: Help! Question about eyes and light angles
Posted: Wed Dec 11, 2019 12:59 pm
by El Pollo Diablo
This presentation gives some fields of vision for some animals
https://www.slideshare.net/VaniJhaveri/ ... in-animals
Re: Help! Question about eyes and light angles
Posted: Wed Dec 11, 2019 1:22 pm
by Fishnut
It is. I'm trying to measure the visual field of fossil fish, so I'm having to guestimate on how much their eyes can move in the socket and then also guess whether a light beam from a particular angle, even if it hits the pupil, is at an angle that can be detected. I don't know if I'm overthinking the latter part - maybe all light that hits it gets directed in, I'm not sure.
Re: Help! Question about eyes and light angles
Posted: Wed Dec 11, 2019 1:35 pm
by El Pollo Diablo
Right, of course. I forgot about eye movement itself.
If you look at the link above, there are some presentations there from people who seem to have looked into this. You might be able to contact them?
Alternatively, maybe there's some sort of optical research person somewhere going on you can get in touch with?
Re: Help! Question about eyes and light angles
Posted: Wed Dec 11, 2019 1:35 pm
by dyqik
That really depends on the lens and retina, and where the receptors are.
In any case, within the total visual field, there's varying visual acuity. e.g. I can respond to bright lights at 90° from my direct line of sight, but I can't resolve anything much, or do much with detailed information from that angle. The light needs to hit my fovea to make useful images.
Re: Help! Question about eyes and light angles
Posted: Wed Dec 11, 2019 1:37 pm
by Martin Y
It does appear, from the links posted, as if a rule of thumb might be that from any angle you can see the animal's cornea, you're in its peripheral vision. I suppose that makes a simple kind of sense as you don't want to expose a delicate structure to damage unless it's doing useful work by being so exposed.
Re: Help! Question about eyes and light angles
Posted: Wed Dec 11, 2019 2:09 pm
by Fishnut
Thanks for all the help and suggestions, it's been really useful
dyqik wrote: Wed Dec 11, 2019 1:35 pm
That really depends on the lens and retina, and where the receptors are.
In any case, within the total visual field, there's varying visual acuity. e.g. I can respond to bright lights at 90° from my direct line of sight, but I can't resolve anything much, or do much with detailed information from that angle. The light needs to hit my fovea to make useful images.
We're also trying to measure visual acuity separately, though again it's all estimates as we have no idea how dense the photoreceptors are. We're having to make estimates based on extant species but there's quite some time, and evolution, between now and when my fish were active (~370my!) so it's all very rough. Still, it's the best we can do with the data available.
Re: Help! Question about eyes and light angles
Posted: Wed Dec 11, 2019 4:39 pm
by JQH
For one horrible moment I though theorist had returned!
Interesting thread - I like reading stuff by people who are doing actual research.
Re: Help! Question about eyes and light angles
Posted: Thu Dec 12, 2019 11:56 am
by El Pollo Diablo
I found a paper by searching for "perimetry in fish", but it might be total bollocks. Don't wish to suggest things you've already searched for, but I'll share in case it miraculously happens to be both new to you and useful.
https://www.researchgate.net/profile/Da ... thways.pdf
Re: Help! Question about eyes and light angles
Posted: Thu Dec 12, 2019 12:38 pm
by bmforre
I have the interesting book
Visual Ecology
Princeton University Press 2014.
Visual ecology is the study of how animals use visual systems to meet their ecological needs, how these systems have evolved, and how they are specialized for particular visual tasks. Visual Ecology provides the first up-to-date synthesis of the field to appear in more than three decades.
Lots of detail on diverse types of eyes, functioning and performance.
I also own
Animal Eyes
Oxford Animal Biology Series, second ed. 2012.
I have worked in optics and bought these out of interest.
Re: Help! Question about eyes and light angles
Posted: Thu Dec 12, 2019 12:55 pm
by Gfamily
dyqik wrote: Wed Dec 11, 2019 1:35 pm
That really depends on the lens and retina, and where the receptors are.
In any case, within the total visual field, there's varying visual acuity. e.g. I can respond to bright lights at 90° from my direct line of sight, but I can't resolve anything much, or do much with detailed information from that angle. The light needs to hit my fovea to make useful images.
For static images yes, but the eye/brain can trigger a strong response to movement/flickering away from the central field. Particularly for 'prey' animals
Re: Help! Question about eyes and light angles
Posted: Thu Dec 12, 2019 1:23 pm
by dyqik
Gfamily wrote: Thu Dec 12, 2019 12:55 pm
dyqik wrote: Wed Dec 11, 2019 1:35 pm
That really depends on the lens and retina, and where the receptors are.
In any case, within the total visual field, there's varying visual acuity. e.g. I can respond to bright lights at 90° from my direct line of sight, but I can't resolve anything much, or do much with detailed information from that angle. The light needs to hit my fovea to make useful images.
For static images yes, but the eye/brain can trigger a strong response to movement/flickering away from the central field. Particularly for 'prey' animals
That's what I meant by my being able to respond to bright lights at high angles. You need contrast and change to respond to that - brightly lit motion, for example.
Re: Help! Question about eyes and light angles
Posted: Mon Dec 16, 2019 12:43 pm
by bmforre
Fishnut wrote: Wed Dec 11, 2019 11:53 am
I have a question that I'm having trouble answering and would appreciate some help. I need to know what is the maximum angle that light can hit the pupil and still be seen by the eye.
So, in my crappy drawing below the green line can be easily seen, the orange line just seen and the red line can't be seen.
eye.png
I need to know at what angle the light can no longer be seen, and how much it varies across species (I'm interested in fish but will take any vertebrate if need be).
What assumptions are you making about index gradient in the fish eye lens?
See
Optics of the Spherical Fish Lens quoted via a course from MIT.
This is discussed in evolutionary context in "Animal Eyes" chapter 4: Aquatic eyes: The evolution of the lens.
https://www.oxfordscholarship.com/view/ ... 0199581139
It is very important for animal vision in water.
Re: Help! Question about eyes and light angles
Posted: Mon Dec 16, 2019 6:15 pm
by jimbob
You can demonstrate that to yourself
Re: Help! Question about eyes and light angles
Posted: Mon Dec 16, 2019 8:43 pm
by Martin Y
jimbob wrote: Mon Dec 16, 2019 6:15 pm
You can demonstrate that to yourself
Now that IM has accidentally got two super fisheye lenses (
viewtopic.php?p=9300#p9300 ) he can rig up some goggles so he can see absolutely
everything.