"Perspective" is a more correct term than "distortion", but yes, you're
correct.

 You're correct.  It doesn't act *completely* like a 75mm lens, having some
minor differences to quibble about (like a longer DOF), but in terms of
perspective, you are correct.

 Yes.  One of my friends does all of portraits with his EF-S 60mm f/2.8
macro.  That's a VERY sharp lens.

steve

Actually I learned not too long ago that perspective is relative to
distance or position from the subject, not focal length, so a wide angle
lense can be used if you're properly positioned from the portrait
subject.

Based on my years of 35mm film lenses, I had wrongly presumed that the
"distortion" of a wide angle and the "compression" of a telephoto were
universal, but it depends greatly on the subject distance.

Google "lens perspective" and you should find lots of info.

It turns out that a 50mm f/1.8 is a decent portrait lense on a DSLR. The
effective field of view crop is similar to a 75-80mm lense, and due to
the large aperture it has a very shallow depth of field.

Yes.

I believe so.

Yes.  Allowing, as you say, for personal preference and such, those
are valid rules of thumb for the 35mm film / full-frame digital
domain.

When shooting a Nikon 1.5x crop factor body or a Canon 1.6x crop
factor body.  The 4/3 system has something like a 2.0x crop factor.
Canon also makes 1.3x crop bodies (the 1DmkII currently).

Yes.  The factor is best thought of as changing the field of view,
really.

Note that the depth of field you get at various apertures will *not*
be what you expect, quite.

Pretty much; though I note in passing that people have strong
preferences among lenses of the same focal length soemtimes.

Yes.

If you are interested in how the "perspective" thing with shorter
focal lenghts works out in practice, take a look at this webpage,
for a pictorial example: http://hannemyr.com/photo/crop.html .
(Scroll down to the section "perspective").

The distortion you speak of is the relative distance of objects. Your eye
perceives objects at different distances as being different sizes. If you take a
picture with a lens and all of the objects look the same as if you had used your
eye, you would say the lens has no distance distortion. With a 35mm cam, this is
usually a 50mm lens

If you use a 200mm telephoto, things far away will look bigger. A mountain 10
miles away will look maybe 3 miles away, But your wife, standing 1000 feet from
you, will NOT look 7 miles closer! That's obviously not possible, but she will
look somewhat closer, therefore it can be concluded that the image from a
telephoto is of a scene that does not exist. The distances of objects are all
wrong, and not in a linear fashion, more of a 'percent of' fashion

Now as for the effects of digital 'small size' sensors, it is NOT correct to say
that a 50mm becomes a 75mm on a DSLR. The proper term is "crop factor" - the
small sensor crops off the full view of the lens as compared to film.

So if you use a 50mm lens, you will get a non-distorted distance view just like
your film camera - but the edges are cropped off. It gives the same FRAMING as a
75mm, but that's all.

A 24mm lens is still a wide angle, and will give you distance distortion just
like your film camera, but the edges will be cropped off. It will be the same
size photo as if you used a 36mm lens, but IT IS STILL A 24MM LENS, WITH A
CROPPED END RESULT PHOTO!

So the question for you is - can you get a good portrait with a film camera
using a 60mm lens, that you crop 75%?

The lens will still give you the image you are used to with a film camera, but
you will have to move back to accommodate the new framing of the cropped digital
image,  Will you like the results? You got to try it! Moving back will lesson
the distortion you do get, but maybe you want MORE distortion?

Ponder this:  A 40mm becomes a 60mm on your camera. So does a wide angle lens
become a telephoto?

No, it merely gets cropped.

Bob

PS my Nikon D70 went tits up and is in the shop.  Bummer.