As an architecture photography fan, I also like distortion free images.
I would like to share with you my lightroom correction process and some questions I have in that regard.
Please comment with your experience.
I know, we are cutting hairs here, but isn't the devil hidden in the details !
Correcting a lens in a Raw software like Lightroom is quite simple.
Setting the lens correction profile to 'default' just works.
Lightroom finds the right lens if listed in it's DB (as a Leica S user, I'm all set) and applies the distortion correction.
But it's possible to refine that setting via the 'distortion amount' setting:
If you look at the spec. sheet of your lenses you'll see that the relative distortion varies with the focus distance.
The Leica S 24mm lens has up to -5% of relative distortion at close focus distance. At infinity a relative distortion of -2% remains:
For the 100mm S we have -0,5% of rel. distortion at close focus distance and +0.5% at infinity setting:
Considering those figures, and the willingness to optimize its work, it looks necessary to change the amount of the default Lightroom distortion according to those specs.
It's more or less a guess work as there is no distance scale that comes with this Lightroom setting and precisely correcting the 24mm is not always that straightforward for architecture work.
Having the lens spec in mind however is a good guide to optimize the default '100%' lightroom setting.
Moreover if you look at the 24mm S graphs you'll also see that the relative distortion not only reduces with the distance but also changes from shape (increase more around 21mm, less in the far corners).
What isn't clear to me is on what base does Lightroom applies the distortion correction:
Is it based on the infinity distance distortion graph or close distance graph ?
Or on an averaged graph ?
Would be nice if increasing/decreasing the distortion amount let you travel between the extreme close/infinity focus points graphs !
But even the remarkable Alpa distortion correction tool (that takes sensor position in the image circle into account for T/S lenses) does not take distances into account.
So is the focus distance a negligible variable ?
What's your experience/process to deal with distortion correction ?