RE: [photo-3d] Re: Newbie question-near point distance

["Gabriel Jacob" <gjacob@xxxxxxxxxxx>]

Dr.T writes:
>If you have a very familiar subject (like a portrait) you
>can see where this principle fails.  Things closer to the
>camera (nose) appear smaller.  Things further from
>the camera (ears) appear larger.  Here is why:  By
>using long lenses, I fool my viewer into thinking that
>I am closer than I really am.  If I were closer, the nose
>should be bigger and the ears (being further from me)
>smaller.  But because I am really far away, the size
>does not change.  Hence they perceive the opposite 
>effect (small nose, large ears).

Two thumbs up on your explanation! Another easy way
(at least for me) to visualize this is to form a rough
frame with one hand and look through it at your other
extended out thumb. Moving your framed hand and head
closer, your thumb will look like it is getting
progressively bigger relative to it's background. This
is analogous to using a fixed focal length and moving
the camera closer in.

Now instead keeping your head at a fixed distance, you
move only your framed hand closer to your extended
thumb. The thumb will now remain constant in size,
relative to it's background. This is analogous to
zooming in with a variable focal length camera. It
magnifies the image in the frame but it doesn't make
it (strictly speaking) look closer. 

I remember trying out an interactive photographic CD,
a few year back. It supposedly let you adjust a virtual
camera and see the results on your computer. I was 
disappointed and mildly shocked when I tried moving the
camera closer to the scene and all it did was magnify
it!

Gabriel, trying to put things in perspective! ;-)


 

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