I wrote earlier on the limitations of the human eye, and why it makes for a very poor photodetector, when compared to other photodetectors that we currently have. The earlier blog entry dealt with the response bandwidth of the human eyes, and the quantum efficiency.
This time (no pun intended), we will deal with the response time, which will produce the time resolution, of the human eye. We all know that when we go see a movie, it is nothing more than a series of still-image frames, moving past us fast enough that we do not see its motion, but rather see the image as being continuous. Standard movie frames (at least till all the new advancements in movie projection) used to go at 24 frames per second (FPS). This translates to 0.04 second per frame. We also know that the human visual system holds an image for about 0.02 second. It means that anything that comes into our visual system faster than 0.02 second will not be perceived as being distinct. So the 0.02-0.04 second is roughly the time resolution of the human eye.
Now, compare this to other devices. I've listed before some typical photocathodes used in accelerators. Note the time responses for the various types of photocathodes. The worst of these are in nanoseconds. This is still order of magnitudes shorter than the human eye! One example is GaAs, which is a common photocathode use in both accelerators and photodetectors. On Pg. 25, one can see measurement of the time response. The full-width-at-half-maximum of this photocathode is of the order of picoseconds!
So the human eye is not only a bad detector in terms of its bandwidth range and also in terms of sensitivity, it is also a very SLOW detector and can't separate a series of event occurring faster than 0.02 second!
Zz.
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