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[OM] More DxO, better news - update

Subject: [OM] More DxO, better news - update
From: Moose <olymoose@xxxxxxxxx>
Date: Mon, 14 Jul 2014 22:46:27 -0700
On 7/14/2014 5:00 PM, Mike Gordon via olympus wrote:
Linear Moose writes:
I happened to have some shots of engineering drawings taken at a meeting with 
GM1 and 12-32 @ 32 mm, close focus.
I've got a lot going on today and tomorrow before we head out, so I don't know 
if I'll be able to post examples.

Quick summary:

LOTs of barrel distortion without correction.
ACR correction using data from the lens itself is much better, but distortion 
is still evident.
Manual correction added in ACR gets quite close.
The DxO lens module correction is just about perfect.

Hmmm, very interesting. Thanks for the quick post before you leave.

I recall you wrote that turning off the whole distortion module in DOP led to a 
result similar
to metadata use in ACR---very odd as I don't recall that effect at all with Canyon lenses--but no metadata available either.

I said that? I guess it's what I thought at the time. Probably fooled working with a lens with very little pre-correction distortion. With 12-32 @ 12 mm, turning the DOP correction off gives a pure optical image, and quite a bit of barrel distortion.

The lens profiles in ACR with Canyon lenses seem to allow for 0-approx 80% correction and DOP from 0-100%--at the price of more pixel torture and change in FOV. An easy price to pay in many circumstances. DOP certainly quick and effective for this full correction and the converter itself is not bad. The degree of correction should be up to the photog and not determined by arbitrary metadata with the lens.

There is the argument that the correction is part of the lens design. Knowing that linear distortion would be corrected, the lens designers were free to let distortion take a back seat to other corrections and design criteria. Using the uncorrected image is like reversing an element in the lens itself.

I imagine that's part of what allowed such a tiny, but high IQ, 12-32 zoom. Sounds harsh to call the metadata distortion info arbitrary. The lens designers who worked so hard on the lens might feel dissed. :-)

OTOH, shooting Raw and using some converters other than ACR, as with DOP, gives 
you the choice.


The Marnie shot I had started working on pursuing a similar analysis had many straight lines but was taken at much longer distance with the 12-32.

Well, no intentionally shot test images for my just now. The truth is, I seldom need perfect correction for my sort of shooting. Then there's the elephant in the room - what effect does all this have on details? I recall a landscape where whatever correction I was using took a recognizable item in a far corner and distorted it beyond recognition. With a lot more pixels these days, I suspect it's not so big a problem as it was in 6 MP days.


PTLens has profiles for most of the 4/3 and µ4/3 lenses, which I haven't tried 
yet.

I believe it is optimized for focus distances over 10 ft--not sure how it would 
perform at near MFD.

That's true, according to the specs for taking test shots.

However, I just downloaded the latest profiles, including the 12-32. PTLens does a very good job on my test image. With them on layers, so I can switch rapidly back and forth, I'd say the DOP version is ever so slightly better, but I doubt anyone would ever notice in other contexts.

Oddly enough, the DOP seems somehow slightly less clear on text, esp. in the corner. Both have a little purple fringing, carried over from the uncorrected version, which seems slightly worse in the DOP one. Very subtle stuff, and I'm not investigating CA differences here.

Alternatives Moose

--
What if the Hokey Pokey *IS* what it's all about?
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