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[OM] Super wide zooms [was Re: E-410 Kit]

Subject: [OM] Super wide zooms [was Re: E-410 Kit]
From: Moose <olymoose@xxxxxxxxx>
Date: Thu, 07 Jun 2007 20:45:35 -0700
Chuck Norcutt wrote:
> You're making it harder for me to resist buying this lens.
>   
Maybe I can help  ;-) 
------------------------------

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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