re: focal lengths

[P3D John Bercovitz <bercov@xxxxxxxxxx>]

> John B:
>> Actually, using a longer lens doesn't simulate
>> being closer to an object unless the object is flat.

> Huh?

OK, you have a wall fresco.  You set up your SLR with
50 mm lens on a line perpendicular to the center of it 
and take a shot.  Next you put on your 100 mm lens and
step back to twice as far from the wall and take another
shot.  The two shots are indistinguishable.  This is
what you're talking about.

Now you do the same thing but you're taking a picture
of something with some depth, say a statue.  You take 
a picture with the 50 mm lens and blow up the neg 10X
so you can view from a 500 mm center of perspective.  
Everything looks right.  Without moving the camera you 
shoot with the 100 mm lens and also blow it up 10X and 
view it from 500 mm.  Now the statue looks flattened 
in depth because you're viewing from too close.  So you 
back up to 1000 mm and view it from there and everything 
looks fine but now you're no "closer" to the statue than 
you were with the 50 mm shot.  That's what I'm talking 
about.  In other words, shooting with the longer lens 
doesn't really simulate getting closer; you gotta get 
closer to simulate getting closer.  It's a perspective 
thing.

John B


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