I Have Lens Envy

Quick Pre-Post Note to Salt-Lake Area Night-Riders: Last night my buddy Fast Jimmy and I rode the Glenwild/Flying Dog/24/7 loop up in PC. Frozen, fast, fantastic. 24/7 especially when frozen is the fastest, smoothest, best-traction singletrack you’ll ever experience in Northern Utah. With the change in weather coming, you just might (if the snow holds off long enough) have one last chance to ride it this year- tonight, Wednesday 11/26/08. Do it. (But only at night- it’d be a mud-bath by day…)

So last Saturday I was out poking around the Oquirrhs with Professor Chuck and Rudy Drobnick, taking some measurements on a new hybrid oak clone Rudy found (circled yellow in photo to right of Rudy), and trying to relocate another he found 50 years ago but since “lost.” And while we were scanning hillsides, Rudy loaned me his binoculars (circled red in photo) for a moment. The binoculars were these (below left), the Zeiss 10x40, and within 10 seconds of using them I was struck with a level of object-lust I haven’t experienced since the 80’s, when I was really into motorcycles.

I’ve had several sets of half-decent binoculars over the years, but none of them were anything like this. The view through these was amazing: crisp, clear and steady. It was like the way binoculars work in James Bond movies, where 007 picks up a pair and watches the bad guy program the detonator codes from a mile away. Or like the way I imagine foveal vision works in birds. Foveal vision in birds is one of those ultra-cool things in the natural world that I need to get around to doing a post about sometime. Oh hell, let’s just do it now-

All About Foveae

The fovea is a teeny central patch about a millimeter across in the center of the retina of your eye. In the fovea, rods and cones are packed way more densely together than over the rest of the retina. (This close-packing is achieved in part by making the rods & cones smaller.)

The increased density of receptors allows for the formation of a sharper image. It’s always the focus of our vision, which is the reason why things are always clearest when we center our field of vision on them.

An Experiment

Tangent: Here’s a simple experiment to convince yourself that human eyes have foveas. It’s both easy and a great time-killer at work, so try it.

OK, wait until nightfall, break into a morgue, then- haha! Just kidding. No, put 2 pens, each with legible brand names on them- like “Sharpie”- on a table, 1.5” apart. Position your eyes 18” above the table and pens.

With your eyes focused on one of the pens, you’ll still be able to clearly read the brand name on the other pen.

Now position the pens 6” apart. Position your eyes 18” above the table…

…and with your eyes focused on the first pen, try to read the brand name on the 2^nd. You can’t do it.

Now you may think, well hey that’s just because I’m not looking at it. But you are looking at it. You can see how long it is, how wide it is, and how far it is from the 1^st pen; you just can’t read the writing on it, and that’s because although the pen is in your field (specifically in your binocular field) of vision, it is not in your foveal field of vision. Cool, huh?

Disclaimer: OK, so this isn’t like a “real” experiment I found in a book or on Wikipedia or anything. It’s just something lame thing I cooked up screwing around at work while on a conference call. So if it doesn’t work for you then hey go buy a real science book or something.

3 Cool Things About Foveae

So here are 3 really cool things about foveae.

Tangent: Ever notice how I always enumerate when I’m making a point or explaining something? I do that in real life, too, and in fact sometimes my coworkers make fun of me for it. I wonder why that is… (I can think of 3 possible reasons…)

First, of all the mammals, only primates have them. And specifically only Simian primates, which means just monkeys and apes. So just like we have better color vision than pretty much all other mammals (“we” in this case being us and our ape/monkey cousins) we also have the only foveal vision among the mammals.

Second, just as birds blow us away in color vision, they similarly trounce us in foveal vision. Birds (and many reptiles) do have foveae, and the foveae of birds are packed way more densely with cones and rods than are human foveae, Our foveae have about 200,000 receptors per square millimeter. A hawk’s foveae have around 1,500,000 receptors per square millimeter.

And third, our entire field of foveal vision is within our binocular field of vision. But lots of birds’ eyes have a second fovea, positioned to provide foveal vision outside of the forward-facing binocular field. This is monocular foveal vision and it greatly helps birds such as hawks and eagles identify motion and prey in their peripheral field of vision as well as judge speed and distance- both their own and that of things they’re watching/chasing.

Rudy doesn’t strike one as a man of expensive tastes. He’s the last guy you’d think of to wear a Rolex, drive a Lexus or even drink Starbucks. But these binoculars run $900. Wow, that’s a lot of money. But the view was sooo good… What to do…. what to do… I will be stewing on this one for a while…

PS: I’ll probably be offline for most/all of the long weekend. Awesome Wife, the Trifecta and I are headed down South. But as always, I should come back with some good material. Have a great Thanksgiving.