At 10:05 1/26/01, Sam Shiell wrote:
Now, a stoopid question... what would be the benefit in getting a 50mm,
apart from an extra f-stop, when I already have a "prime" zoom that covers
this, and also allows me to stay still and get the framing right? As I've
had the zoom for so long I'd can't see that I'd use a fixed standard very
much.
[snip]
Any further opinions?
Zooms are always some form of compromise versus prime lenses. However, I
won't claim you need any primes if your zoom(s) are not preventing you from
achieving your vision for your images. That is the important consideration.
I did note your comment that a zoom "also allows me to stay still and get
the framing right." I view focal length as primarily perspective
management. Perspective is how the size scale of closer objects compares
to the size scale of more distant objects and how rapidly that scale
changes with distance. With a long lens, the perspective flattens image
depth. With a short lens, it increases the perception of depth. This
includes controlling size of a background compared to a subject in the
foreground. By moving farther back and increasing focal length, an object
in the background can be made larger while keeping something in the
foreground the same size. Similarly, a shorter lens can be used to do the
opposite. I will admit changing focal lengths for distance management
(framing) when it isn't possible to move, but only when it isn't
possible. A couple of examples:
1a. http://johnlind.tripod.com/oly/gallery/om61.html
Moved back and shot this with a 200mm to get the distant bluffs taller than
the tractor to provide it a solid background instead of the tractor
stradling the horizon. Make note of the size of the fence posts and
distant bluffs before viewing the next one.
1b. http://johnlind.tripod.com/oly/gallery/om64.html
Moved forward and shot this with a 135mm to get the farmer and tractor the
desired size compared to the fence posts used to frame the
photograph. Note that the fence posts are the same size and the distant
bluffs have shrunk in size! These are the _same_ fence posts and bluffs as
in the first image.
2a. http://johnlind.tripod.com/oly/gallery/om44.html
Shot with a 50mm for a perspective much like a human would see, and keep
the pedestrian (me) more connected to the city (his destination); a feeling
of being on the edge but not in the middle of it. [Needed a pedestrian for
this one and nobody else was fool enough to be out there that late at night
in zero degree weather . . . so I provided myself using tripod and
self-timer. Not much chance of getting mugged that night :-) ]
2b. http://johnlind.tripod.com/canalwalk/cw27.html
Shot from almost exactly the same location as the first with an 18mm to
greatly increase depth, make the city look much more very distant, and
isolate the couple as much as possible from the busy city with all its
noise and activity.
Just happened to have these two pairs of images that demonstrate how focal
length can be used for perspective management. It can be useful for
technical reasons (making the bluffs taller than the tractor) or completely
change the the mood of a scene (second example).
-- John
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