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

Started Nov 10, 2012 | Discussions thread
Barrie Davis
Barrie Davis Forum Pro • Posts: 21,460
Re: Not the 50mm myth again. That one is tough to kill!

JulesJ wrote:

Barrie Davis wrote:

I think a normal lens is one half-way between wide-angle and long-focus (tele), meaning it isn't either. It happens this f-length will approximate the image diagonal dimension.

That's ALL I think it is.


I don't think such a lens has a "perspective that's like human vision", because lenses, whether on cameras or on the front of the head, don't have perspectives... It is positions in space that have perspectives.

Neither can any one focal length match human vision for Field or Angle of View,

I think it does.

I know you do, but I think you are mistaken.

because human vision constantly adapts how wide is the view it perceives depending on the seeing job it's carrying out.

I don't think it does. We do not zoom in and out.

And I think it does. In effect, dynamically "zooming in and out" is EXACTLY what we do, the effective field width being that which we scan our eyeballs over.

It isn't an idea I came to by myself.

This was all part of a most interesting and informative lecture I attended on "Light, Colour and Vision" presented at the University of Surrey to local members of BIPP..

About 8 years later a good deal of the material was part of a "Horizon" documentary about how we see, with the original Surrey lecturer being one of the on-screen talking heads.

All we have is looking, ie the direction we concentrate on and focus. (we also have auto f-stop as in our iris bit this makes no difference in this example)

Furthermore, we only have to look out through our own eyes to know for certain there is absolutely nothing resembling a hard framed limit to normal vision when taken as a whole. About 90° round to the side it FADES OFF to nothing after growing increasingly blurred at the limits.

We don't need a photographic training to see this..

What you are talking about is the crop of what we see. This is circular and as you say fades at the edges. ie a vignette.

"Cropping" and "zooming in" are not significantly different from each other when we appreciate that all the perceptive processes we are talking about take place in the brain, not in the eyeball.

I am sorry we "see" this differently, Jules. ... but I'll get over it.

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"Ahh... But the thing is, these guys were no ORDINARY time travellers!"

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