Wow! Thanks! That was a lot of work to illustrate the point. I'd love
to have a Zuiko 18 and 21 but I don't think I can justify the expense at
the moment. My Zuikos stop at 24/2.8. I used to have the 24 shift but
sold it to John King thinking I was going to buy a 20D with small
sensor. Then I dallied and dallied waiting for Oly to do something and
finally turned to the 5D instead. By that time one of my reasons was to
have enough pixels to stand up to the losses for software geometry
corrections given that the 24 shift was gone.
I do own PTLens but need to do some test photos and have a couple custom
profiles created. I was going to do that last year but it got lost in
the moving shuffle. But I think I found the perfect building for test
images the other day so have to get back on it.
I was quite surprised at the amount of barrel distortion and also the
effect on non-architectural images. After reviewing lots of lens tests
over the past several days I'm thinking more and more of using a 17/18mm
prime and restricting the zoom to 20-35 or 20-40.
Anyhow, I was very glad to see that the 17mm distortions on the Tamron
were straight forward barrel distortion and easily corrected in software
vs. the more troublesome sinusoidal oddities exhibited by some lenses.
Chuck Norcutt
Moose wrote:
> 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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