Hmmh…
The handler stood in the center of a square thing, sharp red on the dark green lawn, about 2 meters side width, about ten meters side length… even we humans should see this, hundreds of meters above.
Probably the training system for the eagle…
For the sharpness of the the eagle’s sight, OK.
My dog had a really low sharpness at distances… I had to shout or move the arms for allowing him to see and recognise me at 50 meters….
On the topic of dog vision, I generalize, because there are great breed variations in vision, like most other physical characteristics in this species that has been subject to so much “designer” breeding on top of what evolution endowed it’s ancestor, the wolf, with.
Dogs are a whole different kind of situation as far as retina anatomy and visual functioning. Dogs don’t have many cones at all (high light level sensors of variable spectral sensitivity), maybe 3% of their total photoreceptors. They have an almost all rod retina without a fovea (the central area of concentrated cones that makes the difference between 20/20 and 20/200—in the rest of the retina—in a human.
Dogs do have some fine point to point organization of their rod retinas, and some cones, however, so can manage to perform daylight visual acuity estimating tests at about ⅓ of human acuity (about 20/60–20/70). Obviously, the so-called “sight hunting” breeds (greyhounds, afghans, etc.) are better at this than others.
But what the dog’s all rod visual system really excels at is capturing motion. If you spend much time with a dog, you’ve undoubtedly seen this phenomenon: Out walking with my Irish Water Spaniel, who is an avid small animal predator, I will see a rabbit at, say, about 60 yards distance in a field. The rabbit, having spotted us, is frozen. I’ll try to point him out to my dog, and he looks around but obviously doesn’t see him (and he’s downwind). So I take a step toward the rabbit and, in a flash, the rabbit shifts into high gear and is off running. The instant that rabbit moves, even if my dog isn’t looking directly at him, he sees him and he’s off running at his top speed too!
He almost never catches them, but this illustrates what the dog’s visual system is really good at: picking up ANY motion of even very small object that, if motionless, he is unable to resolve to a level that registers in his visual consciousness. And most dogs are even better at this in low light levels. Just like your peripheral rod retina is the most sensitive to very low lights at night.
And, dogs have a tapetum, a highly reflective layer of tissue behind the retina, so incoming photons bounce off and go back through the cone layer a second time, effectively doubling the effect of each photon. (the tapetum being what makes you dog’s eye “shine in the dark” when you hit him with a flashlight)
The low light sensitivity of rods has to do with both the pigment they contain and their particular cell anatomy. The motion sensitivity is probably produced by the way they are “wired” to each other and to the visual cortex of the brain.
Optically, most dogs (at least most I have measured) are myopic…their eyeballs are too long for the focal length of their lenses. But sharp focus doesn’t mean much if you don’t have a cone retina with a fovea. In fact, diffusion of the focal point might even help with that ability to pick up tiny, dimly illuminated motions that are not in the direct line of sight.
Dogs also have a visual pigment that is more sensitive to blue and even ultra-violet light, and have a visual pigment in their photoreceptors (cryptochrome) that is suspected to possibly be the source of magnetic field sensing in birds…so maybe in dogs (and humans?) IF they have magnetic sense.