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07-09-2013, 01:56 PM   #1
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Real Life Focal Distance

Here is a real newbie question. When using my K-30 and my 18-55 mm kit lens, it looks like a focal length close to 55 mm is equivalent to a real life view. Is that right? Does this vary with different lenses?

07-09-2013, 02:07 PM   #2
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I'm not sure what you mean by that, exactly. Conventional wisdom holds that the diagonal measurement of the camera's sensor equals the "normal" focal length, which is supposed to most closely mimic what the human eye sees.

For your K-30 (and any other APS-C camera), that focal length is about 28mm (on film or FF digital, it's 43mm). So, no, 55mm is well into telephoto territory. I'm not sure how they arrived at that conclusion, though, because they eyes definitely do not see the same way a camera sees. If the 55mm length seems most natural to you, there's nothing wrong with that.

This will not vary from lens to lens. 55mm will give you the same angle of view with any lens that covers 55mm.
07-09-2013, 02:42 PM   #3
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I did not think it should be between 50-55 mm. Maybe it is just my eyesight.
07-09-2013, 03:02 PM   #4
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A normal lens is one which provides an angle of view similar to the angle subtended by a large-enough print viewed at a typical viewing distance equal to the print diagonal, typically 53 diagonally.

The 50mm normal lens for 135 FF was decided upon by Oscar Barnack, who designed the Leica and the 135 FF format. A true normal lens would be 43mm but the 50mm was already an established lens design and produced a pleasing enlargement with a 50mm enlarging lens.

07-09-2013, 03:26 PM   #5
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On the other hand, for me 55mm on APS-C is pretty much exactly what I "see", or more like normally concentrate on in my viewing field. I can see way wider than that but 55mm seems to be a copy of the size of the high priority area in my viewing field.. Maybe my brain is a telephoto one?
07-09-2013, 03:41 PM   #6
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QuoteOriginally posted by Kenntak Quote
Here is a real newbie question. When using my K-30 and my 18-55 mm kit lens, it looks like a focal length close to 55 mm is equivalent to a real life view. Is that right? Does this vary with different lenses?
I'm guessing you are holding the camera up and looking through the viewfinder with one eye? And comparing it to what you see with your other naked eye?

If so, this is not a good way to judge focal lengths. The optical viewfinder has its own magnification as part of its design, which affects the relative size and brightness of what you see through the viewfinder. However, this has no effect on the image that reaches your sensor.
07-09-2013, 03:49 PM   #7
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You probably mean that at around 55mm you see through the lens similarly as you would see with the naked eye?
You are kind of right, a lot of people say that 50mm is a similar angle as the human eye's focus is, with similar space compression and distortion. But we are biological creatures, we see a much wider area, but we just don't devote our concentration to it. The eye also has different types of light-sensitive cells, so our eyesight is not uniform. The camera on the other hand is just a 3D image rendered onto a 2D sensor and then interpreted by (in the digital age) computers. So a direct equivalency is impossible.

But odd fields of view are usually attractive to us, because they show us the world in a "new" way. Like very wide angle lenses, macro lenses, or long tele lenses.
07-09-2013, 04:51 PM   #8
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Focal length of about 50mm will provide magnification similar to the naked eye. This is not the same as FOV (field of view) or the technical (arbitrary) definition of "normal". If you like way that things look at 50mm, then that focal length probably resonates with you. What luck, since 50mm lenses are plentiful and pretty uniformly good!


Steve

07-09-2013, 05:18 PM   #9
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QuoteOriginally posted by VisualDarkness Quote
Maybe my brain is a telephoto one?
That's funny! I must have a wide-angle brain, as 20mm on APS-C seems perfectly natural to me. Too bad, it's not as catchy as "telephoto brain."
07-09-2013, 05:19 PM   #10
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Well, this is fascinating. Like VisualDarkness stated around 55mm is pretty much what I "see" in the high priority area in my viewing field. In other words, if I look through the viewfinder at a chair in the distance, it is approximately the same size as with my naked eye.
07-09-2013, 05:28 PM - 1 Like   #11
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QuoteOriginally posted by scratchpaddy Quote
That's funny! I must have a wide-angle brain, as 20mm on APS-C seems perfectly natural to me. Too bad, it's not as catchy as "telephoto brain."
But still better than having "Fish Eye Brain"...

Cheers
Dean
07-09-2013, 05:35 PM - 1 Like   #12
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Or the poor fellows with tilt and shift brains.
07-09-2013, 05:38 PM   #13
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I want a zoom brain!
07-09-2013, 06:21 PM   #14
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QuoteOriginally posted by Dean Bradshaw Quote
But still better than having "Fish Eye Brain"...

Cheers
Dean
I think I have a fisheye brain...

http://www.flickr.com/search/?w=28796087@N02&q=zenitar


Steve
07-09-2013, 08:46 PM   #15
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QuoteOriginally posted by Kenntak Quote
... if I look through the viewfinder at a chair in the distance, it is approximately the same size as with my naked eye.
So, you are holding the camera up and looking through the viewfinder with one eye. And comparing it to what you see with your other naked eye. This is not a good way to judge focal lengths.

The optical viewfinder has its own magnification as part of its design, which affects the relative size and brightness of what you see through the viewfinder. However, this has no effect on the image that reaches your sensor.
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