Your eye and SL: Why it’s all about lenses

Warning: This is going to get a bit techie.

Did you know Second Life is designed for the the human eye and what you see in SL is a simulation of what your eyes would see if your eyes worked the way a camera lens does?

Maybe the former is obvious, but the latter probably isn’t.

Designers of virtual worlds, whether it is World of Warcraft, Tomb Raider, or Second Life, try to replicate on your monitor the way a human would see their world. Seeing the world through the eyes of a cat would be pretty weird, after all.

The human eye is pretty complicated, though. It’s not as straightforward as the lens on your camera. Unlike a camera lens, your eye is curved, most of us have two of them, and our brains get involved in all sorts of ways, all coming together constructing a view of the world that’s basically sharp in the middle and fuzzy on the edges (i.e. peripheral vision).

[Sometimes your brain doesn’t do the best job with constructing what you see. Optical illusions and the blue or yellow dress controversy are examples of your brain glitching out.]

While it’s not possible to  replicate what the human eye sees and how it sees, exactly, it can be reasonably replicated by simulating a camera lens. Because what really matters is what your eyes focus on most of the time: the central view angle of the human eye.

Both our eyes combine to give a fairly wide view angle of about 130 degrees, but we rarely use all that. A great deal of it is peripheral vision and that’s not the part of our vision we focus on.

What we tend to focus on is a smaller view angle from 40 to 60 degrees, so 50 degrees is often thought of as a the central view angle or angle of view of the human eye. The 50 degrees view angle corresponds, roughly, to a 43mm lens, but SL uses a slightly distorted 50mm lens to create your view of the world.

I say distorted, because a normal 50mm lens would have a view angle of .82 (radians), not 1.047. I believe this is done to give you a wider view, more attune to the upper view angle range of the human eye. It’s not a proper 50mm lens, but it is probably done to make your view of Second Life’s virtual world more comfortable.

You can see this yourself in the default SL settings:


A lens is defined by two basic parameters–focal length and view angle. You can see the default lens, the way you view your SL, is set to a focal length of 50mm and 1.047 for the view angle. That’s a slightly distorted 50 lens, but I think it’s closer to how the human eye sees the world than how a normal lens would.

FOV (field of view) is used to adapt your world view to the monitor size you’re using. FOV is defined in degrees and should always correspond to the view angle. 1.047 radians is 60 degrees.

[Note: Foc Length, View angle and FOV should be linked, since Foc Length defines View angle and View angle defines FOV, but for some reason Firestorm lets you play with them to your heart’s content. More on this, later, maybe the next article.]

In the end, for Second Life world designers, what matters is that central view angle of the human eye. They replicate what you see in world by simulating a 50mm lens with a wider than normal view angle, showing you SL as you would see it through your real life eyes. Without all that pesky peripheral vision, of course. After all, do we really need peripheral vision?


Cameras vs. The Human Eye, Cambridge in Colour




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