From: CheekyGeek
As an (important?) aside, I recently bought the Sigma 10-20mm f4-5.6
(used) and read that it WILL cover a full 35mm frame down to 13mm. I
plan on trying this myself with my Z-1p. I'm sure the corners will
suffer, but WOW... a 13mm rectilinear focal length with no
field-of-view crop? If true, it is amazing that they don't promote
this. Lesson: Don't ASSUME your lenses designed for APS-C won't cover
the full 35mm. They just may not do it over the whole zoom range.
Haven't USED it on the PZ-1p, but looking through the viewfinder ...
At 10mm it's like lookin' through a porthole.
At 12mm there's still a tiny bit of vignetting at the corners
At 14mm - 20mm there's no visible vignetting, but there is a slight, but
noticeable, light fall-off at the corners.
The equivalence is more of a shorthand for photographers who were
> accustomed to how 35mm focal lengths worked, and it has really
> outlived it's utility.
Well a focal length is a focal length is a focal length but if you are
an old school 35mm film shooter then a particular lens focal length
translates in your mind to a particular field-of-view. When you crop
that you haven't changed the effect of the focal length (think:
squashed depth with a particular telephoto focal length, for example)
but you HAVE changed the field-of-view. For a radical example
illustrating this principle, put a F 17-28mm fisheye zoom on a Pentax
DSLR. You've still got the fisheye distortion you associate with
ultrawide, but you are cropping the center out of the field-of-view
(an effective 25-42mm with fisheye curves... which can be very
interesting!)
Bottom line, if you think in terms of field of view, AND you used to
shoot film (or you STILL also shoot film), the equivalence continues
to have more than a little utility. It is similar to an older American
who will always need to convert metric units to imperial units in
order to grasp what is being talked about. A younger generation that
simply learned the metric system without having the base knowledge of
imperial units would certainly not need that utility.
Well, the way it's expressed - as an equivalent focal length - is wrong.
It's not an equivalent focal length. Equivalent field of view or angle
of view works, but it's still confusing.
All I really care about is whether the image circle is large enough for
the sensor, be it APS-C or "full frame". I would prefer lenses with an
image circle large enough to cover the "full frame", although I have
some lenses that won't and I still use them ... just not on the film
cameras.
--
PDML Pentax-Discuss Mail List
PDML@pdml.net
http://pdml.net/mailman/listinfo/pdml_pdml.net
to UNSUBSCRIBE from the PDML, please visit the link directly above and follow
the directions.
