"Karl Winkler" wrote in message
om...
David Littlewood wrote in message
...
In this specific case, I could also use two fixed-length lenses (say,
50mm and 100mm), but what about the focal lengths between those two?

In medium format I use a 50mm, 80mm and 150mm- similar FOV to 30mm, 50mm
and 90mm in the "small format", and not far from the 35/50/90mm kit I had in
35mil. I also have a 120mm which I originally bought when I intended having
a two lens kit (60mm and 120mm). In six months or so of working like this,
my 120mm has been gathering dust in a bag like a proverbial Hoover. I just
don't use it, despite the fact that it's probably the sharper lens. The
nearest equivalent to a 100mm in 6x6cm mount is either 160mm or 180mm, and
whilst I have a 150mm I won't consider either as a viable purchase.

Yes, it may seem like a huge jump between 50mm and 100mm, but I doubt
you'll really miss the in-betweenys. And hey, if you prefer 85mm, skip the
100mm and get an 85/1.8 and some tubes.

And changing focal lengths (via zoom or by changing lenses) changes
the *angle of view* of the lens, say from 90 degrees at 20mm to 60
degrees at 50mm to 30 degrees at 90mm (approximately), right? So to
me, this is changing the perspective.

Perspective is not the correct word to use in this sense, and there's no way
around it; no zoom lens could ever be called a perspective control lens.
Zooming is cropping with optics- field of view changes, depth of field
changes, but perspective does not.

With longer lenses, there is
more foreshortening (distant objects seem closer or more "compressed")

This is true with shorter lenses too- and with the human eye. From a
distance, a howling dog can look the same size as the moon whether you're
using a 14mm or 400mm- but a photographer with both lenses will probably use
the 400mm. That fancy effect from "Jaws" and "Goodfellas" was done by
zooming and changing perspective *at the same time*

Google "perspective" and "zoom" in rec.photo.equipment.35mm for more
(heated) past debate on the subject.

--
Martin Francis http://www.sixbysix.co.uk
"Go not to Usenet for counsel, for it will say both no, and yes, and
no, and yes...."