"Moustache" distortion

in the

Olympus 12~40 f2.8  PRO
Zoom lens...

(and it's cure!)








Images & text Copyright by David Young
www.FURnFEATHER.ca

"Moustache" distortion in the 12~40/2.8 PRO Zoom: (Tested on the E-M1 with firmware v 1.1.)


Don't misunderstand me.  I own and love the 12~40/2.8 PRO Zoom.  But there are problems with it and it seems that
most reviewers are not willing to mention them; for fear that they will be cut off future test units.  This is an unfortunate reality for most reviewers.. Fortuantely, for me, I have no connection to Olympus, other than as a satisfied user of many years standing. Thus, I have no such worries! They don't send me loaners for review, anyway!

There has been a trend, in recent years, particularly with micro-FourThirds lenses, to build the lenses leaving a lot of the distortions uncorrected.  Panasonic started this and Olympus has picked it up.  Personally, I think  it's a bad habit.  It does, however, allow their designers to build smaller, lighter lenses with otherwise excellent performance, at a more reasonable cost.

The argument goes that if you're shooting jpegs, the camera will correct the distortion during conversion, and you'll never
see it.  And if the picture is perfect when it comes out of the camera, what more can you want?

Correspondingly, if you shoot raw and develop your images using Olympus Viewer 3, or one of the commercial packages
which have the distortion profiles built-in (and which will automatically correct it during developement) then you'll still
never see it.  So far,so good.

But, what if - like me - you are addicted to one of the more obscure, but very effective, commercial raw developers - such
as Silkypix - or one of the open-source ones - like RawTherapee? Neither of which offer automatic distortion correction.  Now, you have a problem!

For the Olymlpus 12~40/2.8 PRO Zoom suffers from some rather serious, "moustache" distortion!

Now, I've been shooting since the mid-1960's, and I'd never heard of this form of distortion, until recently! So, if you
haven't either, don't feel bad. But it is real and it does exist in the 12~40/2.8 PRO Zoom.

Zoom lenses, by their very nature, nearly all suffer from some Barrel distortion at the widen end, and a bit of pincushion distortion at the long end. How well it is controlled, is really determined by how much you pay!

Look at the image to the right ... at the wide end, the 12~40mm 2.8/PRO has noticeable barrel distortion in the center of the image, but at the edges, the distortion reverses, and becomes pincushion distortion!  Rather a bit like a handlebar moustache!  Hence the term, moustache distortion - though I gather the "correct" term is "complex distortion".

All of this can be mathmatically corrected, if you know how ... which I don't.
 
So I contacted Tom Niemann, of PTLens fame.
But, before I tell you the rest of the story, I'd like to point out that I have no connection with Mr. Niemann, nor PTLens, other than a satisfied customer.

Over the years, PTLens has developed into an excellent, low cost, very fast and easy-to-use program to correct
distortion in all manner of lenses. The lens database includes some 2400 separate calibrations — far more than any
other application of it's type. (BTW: the $25 license fee is good for as many computers as you own and is a one time fee, covering ALL future updates & versions.  Very fair!)


On the PTLens website is an excellent explanation of Pincushion, Barrel and Complex (or Moustache) distortion - with comparisons (Click here) to other, similar, software.  He also has a 10 image free trial, so you can see if you like it, before you buy it.

As suggested by the PTLens website, I took a series of photographs at 1mm intervals, sent them to Tom and he created the correction table for the lens.  (Note that you need not do this ... it needs only to be done once for each lens, and the correction table for the 12~40./2.8 PRO has now been created and is now included with PTLens.)

As you can easily see, from the corrected version of the above image (at right), his program works very well.

Better yet, PTLens is a simple batch processor.  It reads the exif data of each image, disovers the lens & focal length, and then does the correction in fractions of a second.  So, you can go through 40 or more images, in mere seconds.

So, now my workflow is as follows:

1) develop with RawTherapee or Silkypix.

2) Run developed jpegs through PTLens, correcting distortion. (Very Fast!)


3) Resize & use.

In this way, I can process 500 to 600 images, for a client, as fast as I can crop & develop them!

UPDATE!

My preferred RAW developer is RawTherapee, as it is very good, fast, has a comprehensive array of features and it's FREE!  
RawTherapee supports most raw formats, including some unusual ones like those from cameras using Foveon and X-Trans sensors. The latest version (5) has a host of new features, but the important one to this discussion is found in the "Transform" menu.  There you will find a "Distortion Correction" slider.  Just above that is a box labeled "Automatic".  If you click on it, the software will examine the embedded Jpeg (there is one in virtually every RAW file) and make your image match it.  This is possible, because the embedded Jpeg, in virtually every case, has already had it's distortion corrected by the camera.  If, after that, it's still not quite perfect, you can tweak things with the slider, but in my experience, that is rarely necessary.  

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Thanks for reading.

Last updated: 12 November, 2017