Normal eye focal length

For 70 years or more the accepted formula for a "normal" lens has been the length of the diagonal of the frame size. For 35mm film, that is 43.27mm. Leica established 50mm as their normal lens, and most of the rest of the camera world followed suit, giving folks a slight telephoto as a normal lens. Some manufacturers like Pentax put up a small fight and offered a 45mm lens as their normal lens.

http://en.wikipedia.or​g/wiki/Normal_lens

According to the link above, that would make "normal" for an APS-C sensor 30.15mm.

That is why Canon came out with the EF 28 f1.8 - to create a "normal" lens for their DSLRs.

However, if you follow what happened with film, a 35mm focal length would give you about the same effect as a 50mm lens on a film camera.

My 2 cents.

Have Fun,

Ok - If I put my 30mm on and look through it, things seem farther away than naked eye. With the 50, it seems pretty much right on. And that's hands on experience right there.

I don't have a 30mm but things seem a bit closer to my eye when looking through the 50mm.

Mr. Clean wrote:
Ok - If I put my 30mm on and look through it, things seem farther away than naked eye. With the 50, it seems pretty much right on. And that's hands on experience right there.

How "big" you see things through a camera viewfinder - as if you were looking through a telescope or binoculars - really is not strictly due to the field of view of the lens. It also has to do with the optics of the viewfinder, etc. That's why a "normal" lens on your camera (a 28mm to 31mm lens on an APS-C camera, for example) doesn't necessarily provide exactly the same image size as what you see with your eye.

However, the 28mm to 31mm focal length range IS still the "normal" lens focal length range for an APS-C camera such as the Rebel XTi. This is a fact.

What is the f-stop of the human eye?

f/1.2???

My reply certainly wasn't intended as a rebuttal to anyone's comment. It's just that the "normal" label just has always seemed a bit silly to me. There's no particular merit to it that I can discern, and it's only normal inasmuch as enclosing your head in a box and closing one eye would be normal.

Same thing with 1.6, 1.3 and FF. So what? They are just relationships to 35mm. If you've never shot with 35mm film, these really don't mean anything. I've shot with both 35mm and MF cameras. FOV differs between those cameras for various focal lengths. The huge advantage of SLR's is that you can see the FOV photo through the lens before you record it.

Sorry, didn't mean to get off-topic, but to the OP - 50mm was considered by many to be the "standard" lens for 35mm based on it's close relationship to perceived human FOV (with one eye closed and the head in a box)... Keeping that in mind, for a 1.6 crop camera, 31 or 32mm would be the equivalent on the XTi. Not that it matters.


Mark

well i deffinately didnt mean for this to be such a big debate

fStopJojo wrote:
Actually the 50mm FOV = human FOV is totally inaccurate. Barrie and ljfinger are correct, see this http://forums.dpreview​.com …rum=1018&messag​e=17075832

Hmm, that says the human eye has a wider angle of view which is out of focus with an area in the centre of sharper focus.

Sounds like a lens baby should be considered 'normal' then.

Michael.

A 1.6 crop factor does not change perspective. 50mm on a FF body is the same perspective as 50mm on a 1.6 body. The only difference is crop, not perspective.

The human eye is optically pretty poor, but by constantly moving (so-called saccadic movement) and with the brain doing hefty image processing, we end up with a very clear mental model of our surroundings, which we lump together as 'sight'.

With a focal length (when focussed to infinity) of around 35mm, and a maximum pupil diameter of 7mm, that would give something around f/5 for the human eye. However, when you look at something closer, the focal length decreases (the eye lens changes shape), so that would give a faster optical system. I'm not sure what the minimum focal length is, so I can't do the calculation.

Many animals have much 'faster' eyes than us. I once read a cat's eye can open to about f/0.7, but I haven't seen that anywhere else.