lens - How difficult is it to correct mustache-style distortion?

I am considering the Samyang 14mm Ultra Wide-Angle f/2.8 IF ED UMC but I am somewhat concerned about the 5.3% of mustache-style distortion this lens produces.

I like most of what I read about this lens and the primary purpose would be landscape nature/night photography but I also do some architectural photography.

"The biggest weakness of the Samyang is the rather extreme amount of complex barrel distortion (mustache style) which is difficult to correct during post-processing. If you're into architecture photography this will produce headaches." Source: Photozone

I am familiar with correcting barrel and pincushion distortion in post processing but how difficult is it to correct this type of distortion? I would also like to see an example of a mustache-style distortion in an architectural photo. I would appreciate is someone could post one or provide a link.

SOURCE: PHOTOZONE

Answer

It's very difficult to correct by hand, but very very easy for a computer to correct, given a formula for how the distortion behaves.

The reason the Photozone review states that this distortion is difficult to detect, is that most software only offers very simple correction based on radially symmetric distortions based on simple formulas. You can usually only tune one parameter of the correction so you'll never eliminate the moustache.

Therefore you need a piece of software/plugin that can do different types of distortion, along with the parameters of the distortion. If your lens is fixed focal length and the distortion is independent of focus distance (which I think it largely is with the Samyang 14mm f/2.8) then one set of parameters can easily be applied to all images generated by all copies of the lens (that aren't decentered in some way). In this case you can rely on someone somewhere figuring out the set of parameters (usually called a profile) and posting them online.

One such piece of software is PTLens, which includes the Samyang 14mm f/2.8 as one of it's profiled lenses. I believe Lightroom will do such corrections also, with an appropriate profile (here's one, website is in German!)