Chuck Norcutt wrote:
> You're making it harder for me to resist buying this lens.
>
Maybe I can help ;-)
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First, there is considerable linear distortion at the wide end. As far
as I know, all the super-wide zooms suffer from the problem to some
degree. And although identified as barrel distortion by the automated
software that measures it for reviewers, it's really more like what Gary
says about the 21/3.5 "slight waveforming with slight to moderate barrel"
You can see the effect in the 11 mm example from the ZD 11-22 here.
http://www.photozone.de/8Reviews/lenses/olympus_1122_2835/index.htm I
suppose all those numbers below may describe it more fully, but I don't
understand them. :-)
So if you want distortion free super wide, grab a Zuiko 18/3.5.
Predictably, the Tammy 17-35 has barrel distortion with slight
waveforming. Fortunately, it's all pretty easily controlled in software.
There's DxO at the $$ end and PTLens at the $15 end, and a number of
others. As far as I know, PTLens is the only inexpensive app that
includes profiles for most lenses out there - and will do one for others
if you send him a proper sample.
You can see the effect visually in this architectural shot where there
are lots of straight
lines. http://www.moosemystic.net/Gallery/MPhotos/Calif/HearstCastle/CdM01.htm
It doesn't look too bad at first, just a modest bow to the central roof
line if you don't look too close. But when you look at the corrected
version, it's immediately obvious how the whole image sort of bulges
forward in the middle.
By the way, people talk a lot about how digicams can or can't handle
high brightness scenes. I did blow the very top part of the highlights,
but I think the 5D did an admirable job overall once post processed to
pick up the shadow detail. I'd have taken more exposures in this
obviously difficult light, but that fellow in the door is the tour guide
telling me we've just started and I've already fallen behind, which is
verboten. He was required to count us regularly.
You might think, as I did, that this distortion won't matter with
subjects without any obvious straight lines. But at least to me, that
isn't true. I took a number of shots at 17 mm where there is nothing
whatsoever like a linear distortion reference point. When I first
browsed through them, I noticed something just slightly odd seeming
about them. hard to put my finger on it, but something a bit unnatural
looking. Use PTLens, and the problem becomes immediately obvious, the
center portion seems to bulge forward in an odd way.
This is a classic WA use, where it's impossible to get any further away
from the subject. And there's nothing immediately wrong with it; the
correctino is nicer, but no big deal.
http://www.moosemystic.net/Gallery/MPhotos/Calif/Morro%20Bay/Oak01.htm
Here are three shots inside the small, magical canopies of Coastal Live
Oak that only grow to about 12-14 feet, even when quite old, in their
fog belt, sandy soil environment. Roll your mouse rapidly over the edge
of one of these images and you will get quite a clear picture of the
pattern of linear distortion.
http://www.moosemystic.net/Gallery/MPhotos/Calif/Morro%20Bay/OakCan01.htm
http://www.moosemystic.net/Gallery/MPhotos/Calif/Morro%20Bay/OakCan02.htm
http://www.moosemystic.net/Gallery/MPhotos/Calif/Morro%20Bay/OakCan03.htm
------------------------------
Second, lenses this wide really give wild perspective distortion if not
held quite level. Again, the digital darkroom comes to the rescue. I
knew this show was very distorted and, unlike a tall building, where it
doesn't necessarily look bad, it would look like crap. :-P In the old
film days, pre-scanner, I wouldn't have taken it at all unless I could
find something to stand on. In this case, I would have had no time even
if I had something, I had to keep moving. So I took it anyway, framing
in anticipation of correction in post and the loss of some of the width
at the bottom.
Worked as well as a ladder, I think.
http://www.moosemystic.net/Gallery/MPhotos/Calif/HearstCastle/GStair.htm
Moose
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