Bill Grey

When I wrote this:-"

The 50mm lens was/is supposed to represent the human eye's view of the
world. It probably is the best general lens for beginners - forget
landscapes or buildings etc."

Why do have to have interminable inconsequential explanations like this
???

For goodness sake my statement was innocuous and is fair enough as a
general remark!

In message <_e6dnRlwM8jG4vLVnZ2dnUVZ8tXinZ2d@pipex.net>, Paul Saunders
<pvs1@wildwales.fsnet.co.uk> writes
>Mike..... wrote:
>
>>>> The 50mm lens was/is supposed to represent the human eye's view of
>>>> the world.
>>>
>>> I don't think that's quite correct. I believe it represents the same
>>> *perspective* as the human eye, but not the same field of view
>>
>> does a lens have a perspective? I'm sure *you* picked *me* up on that
>> years ago :-) It has a field of view and enables the photographer to
>> move to a position with a different perspective. OK i'm hair
>> splitting :-)
>
>Yes, you're hair splitting, but thanks for pointing it out, since it's
>correct. Technically lenses don't have a perspective, but people talk about
>them as though they do. The effect is real but the explanation is wrong.
>Different focal lengths don't "change perspective", as people say, instead
>they just alter the field of view.
>
>When people talk about lens perspective, what they're really talking about
>how large foreground objects appear relative to background objects. With
>wide angle lenses, foreground objects appear disproportionately large,
>whereas with telephoto lenses, background objects appear disproportionately
>large. A "standard" lens shows foreground and background objects at the
>"correct" relative sizes.
>
>This is of course relative to field of view, which in turn is relative to
>viewing distance. Take an A4 print for example, how far away do you look at
>it from? Do you hold it with outstretched arms? At normal reading distance
>perhaps? I'm sure there's an optimum viewing distance for each size of
>print, but I don't know what it is offhand. (This sort of thing tended to be
>discussed in older, more technical photography books, but no-one ever seems
>to mention it nowadays. I'm sure I've read that there was a "correct" size
>of print for each different focal length - wide angle photos should be
>printed larger, telephoto images smaller.)
>
>So, assuming you're looking at a print from the optimum viewing distance,
>the perspective (i.e. the relative sizes of objects in the image) should
>correspond to the human eye if you took the photo with a standard lens. Now
>obviously that doesn't correspond to human field of view. An A4 print at
>normal reading distance only covers a fraction of our field of view, which
>is much wider.
>
>As I mentioned previously, our field of view, including our periphiral
>vision, is extremely wide, rather like a fisheye lens. But if you take a
>photo with a fisheye lens and look at it on an A4 print at normal reading
>distance, it looks extremely distorted. However, if it were printed at a
>large size on the inside of a sphere, and we looked at that image from
>inside the sphere, at a distance which matched our field of view (so the
>image would wrap around us), then the perspective should look correct (I say
>should because I've never actually tried that!).
>
>One curious aspect of this so-called "perspective" is that it affects our
>sensation of speed. I once put a video camera in my car and recorded the
>view as I drove along a motorway. When I watched it later I was amazed at
>how slowly the car seemed to be moving. This was because I used a wide angle
>lens. Since distant objects look smaller, they appear to be further away,
>hence you seem to be travelling more slowly toward them, even though you
>aren't. With a telephoto lens you'd appear to be travelling faster than you
>actually are.
>
>This is well illustrated with certain types of computer games, such as a
>flight sim. When I fly, I usually use a wide angle view when I want to look
>at the scenery, since that more closely corresponds with my normal field of
>view. However, I find it very difficult to land with a wide angle view. The
>runway looks smaller and further away than it actually is, which makes it
>harder to line up the plane and to judge my landing speed. So when landing,
>I switch to the standard view instead. This gives me a much narrower field
>of view, but that's okay, because I only need to look at the centre of the
>view, i.e. the runway! At this setting the size of the runway looks correct
>and the speed feels right, making it much easier to land due to this
>"correct perspective".
>
>So, while a 50mm lens may look "perspectively" correct, it certainly doesn't
>match our field of view, which is probably why most people (especially
>landscape photographers) prefer to use a wide angle lens.
>
>However, to be even more picky, 50mm isn't even the correct focal length for
>a standard lens on 35mm equipment. Apparently the correct focal length
>should be 43mm (I think), so it should be slightly wider. I can't remember
>the reason why 50mm became the standard, but technically it's wrong. But you
>know what it's like, once something becomes established, it tends to stay
>that way.
>
>Paul

--
Bill Grey