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Old Oct 23, 2006, 4:10 PM   #11
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Quote:

but

50 mm is the focal length of ONE eye (we only use one eye to look through the camera viewfinder)

22-24mm is the "focal length" (note the quote) of TWO eyes, representing the field of natural human vision

??
Yeah, I sort of predicted this discrepancy already. I could hardly believe that the quote of the 50 mm lenses meant our two eyes..that is why you would have noticed that Ihave notdared to add the "s" whenever Iwas talkingabout the "eye".

Anyway, I find that when I used one eye to check, it is still great. :-)I like the subjects to be at such distance, not too far away looking or too close looking; just like that of our vision.
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Old Oct 23, 2006, 4:45 PM   #12
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The 35mm film frame is 36mm wide. If the lens focal length is stated with an absolutemillimeter ratinginstead of 35mm film cameraequivalent you need to multiply by 36 and divide by the sensor or film frame (not film strip) width to obtain the 35mm film camera equivalent.

The traditional "standard angle" for 35mm film cameras is about 50mm, with lesser mm focal lengths being considered "wide angle". This 50mm is said togive the typical field of view of a person.

Most 35mm film point and shoot cameras made in the last 30 years have a "standard angle" around 35 to 38mm, and 28mm is considered a good "wide angle".


Because the retina of the eye is curved (rather than flat) the frame width and also the field of view in degrees is subjective. It is therefore not possible to state a focal length in 35mm film camera equivalent. The absolute focal length isapproximately 25mm or the length of the eyeball


Calculations and comparisons are easier if the cameras/lenses you are comparing both have their focal lengths stated as 35mm film camera equivalents.

Here are some rough field of view angles with 35mm film camera focal length equivalents:

28mm -- 65 degrees

35mm -- 55 degrees

38mm --50 degrees

50mm -- 40 degrees

70mm-- 30 degrees

75mm -- 27 degrees

105-111mm -- 20-19 degrees

140mm -- 15 degrees







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Old Oct 23, 2006, 5:50 PM   #13
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And of course all of the above ignores peripheral vision. Our primary field of view cannot be perfectly defined, but the area of highest visual acuity is as narrow as 2 degrees. Our full field of view and peripheral vision is beyond 180 degrees (full 8mm circular fisheye on a dslr).

Trouble is, this has very little to do with a 'normal lens'. That measurement is more likely tied to the appearance of perspective in a print. That is, a print of a certain size viewed at a certain distance taken with a certain angle of view will appear to have the same perspective as our normal vision. Distant objects will not appear larger or smaller than they should relative to near objects. This standard, while likely flawed and subjective, is a 8x10 print at arms length taken with a 50mm lens on a 35mm camera. It seems that 43-58mm is an accepted range, with different people making different compromises.

An interesting finding, your hand covers about 18-20 degrees at arms length, aproximatly 100mm on 35mm or 65mm on APSC.

Photography and print-making is an optical illusion tailored to our taste.
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Old Oct 23, 2006, 6:09 PM   #14
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Wow this is going beyond photography, into anatomy of the eye and vision that I know nothing about, but thanks for the explanation anyway!
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Old Oct 23, 2006, 8:40 PM   #15
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tmoreau wrote:
Quote:
And of course all of the above ignores peripheral vision. Our primary field of view cannot be perfectly defined, but the area of highest visual acuity is as narrow as 2 degrees. Our full field of view and peripheral vision is beyond 180 degrees (full 8mm circular fisheye on a dslr). ...
It gets even worse: the full peripheral field of view is more than 180 degrees horizontally, but much less than that vertically. And it is larger down than up - unless you are missing the chunk of skull behind your eyebrows.

The basic point is that comparison of the eye to a camera can only be stretched so far. Sort of like comparing a sports car to adump truck - they both run with rubber tires on the same roads and are both powered by internal combution engines. They both have transmitions and steering wheels, but if you try to drive a dump truck like a sports car, you will be in trouble real quick.
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Old Oct 24, 2006, 6:10 AM   #16
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Looking straight ahead, the part of our vision that is always in focus varies between 90mm and 115mm up to130mm, the operative phrase being "always in focus".At the end of your arm though, that "always in focus" area is about 25-30mm wide, or the distance we sit from our monitors.

The evidencecan be had by your looking through a 70-200 or 70-210 zoom lens(any). Looking through the viewfinder, manipulate the zoom until the image in the viewfinder is about theexact same sizeas what you can see with your naked eyes. look at the sacle on the lens.

That's YOUR (individual) "normal" focal length, the angle being comensrate with your normal stereoscopic vision.
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Old Oct 24, 2006, 6:11 AM   #17
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There is another serious problem I think..."Our eye moves!!" :shock::lol:

Yesterday I was experimenting with my camera and eye;

The camera was set at 38 mm and my eye was stated to be at50 mm, hmmm...

I actually found out that my field of view (Of ONE eye only), was considerably broader than the camera's field of view at 38 mm!! And "they" say that our eye is at 50 mm???!!! :?

I actually pushed the camera flat into my face to avoid making the camera seems closer to the scene! However, I still cannot deny that my ONE eye has a BROADER field of view than 38 mm!

This is all getting really tricky; is it because our eye moves?What if we just look straight ahead? (It becomes 50 mm?)

Is our eye really a fish eye? :O

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Old Oct 24, 2006, 6:57 AM   #18
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Eh, I have just found a few interesting links>>>

http://forums.dpreview.com/forums/re...ssage=20564106

http://forums.dpreview.com/forums/re...ssage=20571508

Still rather confused though...:?
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Old Oct 24, 2006, 7:37 AM   #19
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I was thinking along those lines myself. Also, our retinas are roughly hemispherical and cover a large portion of the back of the eyeball; if you could make film or a sensor into that same shape and (proportional) size, the field of view with a 50mm-equivalent lens would also be similar to that of the eye.

AlAsaad wrote:
Quote:
The evidencecan be had by your looking through a 70-200 or 70-210 zoom lens(any). Looking through the viewfinder, manipulate the zoom until the image in the viewfinder is about theexact same sizeas what you can see with your naked eyes. look at the sacle on the lens.

That's YOUR (individual) "normal" focal length, the angle being comensrate with your normal stereoscopic vision.
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Old Oct 24, 2006, 8:49 AM   #20
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Apples versus oranges.

The image size would vary depending on whether you are looking through the peephole viewfinder of a point and shoot camera or looking at the ground glassthrough a 35mm SLR viewfinder or looking directly at theground glass plate at the film plane of an old fashioned bellows camera.

AlAsaad wrote:
Quote:
Looking through the viewfinder, manipulate the zoom until the image in the viewfinder is about theexact same sizeas what you can see with your naked eyes. then look at the scale on the lens.

That's YOUR (individual) "normal" focal length.i
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