>I'm not so sure about that Ken. I recall seeing Zeiss MTF curves on one of
>their early zooms (a 40-80 or so) that seemed to imply that while a zoom
>might get close to a prime over much of it's range, there could be a point
>(or even points) in it's range where it could "surpass" a near equivalent
>fixed lens--because all that glass is in it's "sweet" spot. Another example
>is the 35-80F2.8 Olympus lens--there's no doubt that it has substantial
>barrel distortion at 35 mm and substantial pincushion distortion at 80 mm.
>But that implies there is a point between 35 and 80 where there is NO
>distortion! Would anyone know what that point might be? Because it may also
>be especially sharp (as in very high contrast and resolution/MTFs) there.
As I said in the previous post, you can get the specifications of a zoom as
good if not better than a prime, but the resulting image still won't look
the same. This is especially true with the telephoto focal lengths.
Crazy anology to follow:
A Chevy pickup truck could be outfitted with a mammoth engine, 4WD, and
heavy duty suspension and brakes. It has two seats and so does the Chevy
Corvette. Both have similar 1/4 mile times and both (with good rubber)
have good skidpad numbers. But which one actually feels right whipping
around the twisties on the Pacific Coast Highway?
It all comes down to how a lens deals with what is out of focus. Even two
nearly identical lenses from the same manufacturer (Nikon) one being
internal-focus and the other uses focus by extension will have different
bokeh characteristics.
In an oversimplification a zoom lens uses a different amount of the front
glass surface area to achieve the same results as the prime lens does.
Last winter I took a some identical pictures of a fence at my in-laws' farm
with both the IS-3 and the OMs. I even used the same focal lengths and
lens openings. The resulting images couldn't be any more different! Maybe
I will get them scanned one of these days to show everyone. The OM/100/2.8
combination produced silky smooth images where the critically focused area
blended so smoothly into the out of focus area in one seamless image.
Wheras the IS-3 image was equally sharp at the critical focus point but
produced a disjointed image with the out-of-focus areas. Think Cateye lens
without the donuts.
For an example of what I am describing look at the photograph on page 88-89
(gorillas in tree) of the February 2000 National Geographic.
Ken Norton
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|