When we view an image, is the focal point of our eye on our retina? Shouldn't that hurt? Also, if that is how our eye works, then why don't lenses put the focal point their equivalent retina? I was working with a lens today that had a focal distance of only a few millimeters, however we were using it to record something half a meter away-how is this the case?
Answer
The focal point of your lens is indeed on your retina, when you look at an object far away. If you look at an object closer by, that object is also imaged onto your retina (because you are changing your eye's lens. So it's not really that important whether your lens' focal point is on the retina, but whether you are imaging a given object (sometimes the word focus is casually used for the image location, but that doesn't have to be at the focal point).
Only if the object is very bright (sun, bright small lamp) does it actually hurt. Your retina has a very high dynamic range, much higher than current camera systems.
The dynamic range is the ratio in intensity (or say number of photons) between the brightest object you can still see clearly (say the sun for a very short time) and the darkest object that you can make out against a perfectly black background. This high dynamic range makes it necessary for us to grade intensity in approximately logarithmic terms (Weber's law) when we compare brightness.
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