50mm "Normal" Lens... Ok, but "Normal" on FF or APS-C Sensor?

Started Nov 10, 2012 | Discussions thread
tkbslc Forum Pro • Posts: 11,622
Re: Not the 50mm myth again. That one is tough to kill!

ljfinger wrote:

tkbslc wrote:

If you want to debate "normal" should we also try to debunk "wide angle" and "telephoto"?

Telephoto has a specific meaning - the lens' physical length is shorter than its focal length.

So what about wide angle, then?   And Telephoto's definition has extended to mean any lens longer than a normal prime, regardless of the construction of your lens.  A 300mm prime that is 300mm long would still be called a telephoto by most.

40-60mm lens on FF is typically said to be "normal" because in typical shooting and viewing conditions it results in a perspective that is similar to what our eyes would see. You can come up with scenarios where it is wrong, but in most scenarios it works out that way.

It never works out that way. Your eyes are 180 degree fisheye lenses. The "natural" conditions is when the final image subtends the same angle to your eyes as did the original scene to the camera. That depends on final viewing condition. Those IMAX 360 degree domes that project an image onto the inside of a hemisphere with the viewers in the middle use a circular fisheye as the "natural" lens.

You have a 180 degree horizontal view because your eyes stitch images from two separate lenses that continually scan.   You cannot focus at the peripheral of your vision without rotating your eyes to center on the subject.  It's hard to compare the optical properties of eyes to lenses.

We are really not talking FOV as much as we are perspective.   The normal prime does keep things sized as we expect when shot at the same distance we view them.  When going into telephoto territory, we start to see the background compressed as would be unnatural with the naked eye.   When moving into wide angle territory, we start to see foreground objects unnaturally large.   It's pretty easy to observe with only a few minutes of experimenting.

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