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Thread: Setting the right lens distortion correction

  1. #1
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    Setting the right lens distortion correction

    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 ?
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  2. #2
    Senior Member thrice's Avatar
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    Re: Setting the right lens distortion correction

    Quote Originally Posted by anGy View Post
    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 ?
    With lenses that have fixed cells the distortion profile doesn't change but the magnification does. I think the Alpa tool can analyse and take this into account where relevant. As is clear in the Leica MTF, the floating element introduces a dramatic change in the distortion profile - does the Lightroom correction profile not adjust for this? The S lenses report focus distance to the body.

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    Re: Setting the right lens distortion correction

    Quote Originally Posted by thrice View Post
    As is clear in the Leica MTF, the floating element introduces a dramatic change in the distortion profile - does the Lightroom correction profile not adjust for this? The S lenses report focus distance to the body.
    This is what I'd like to know. From experience I would say no as reducing/increasing the distortion amount in Lightroom sometimes give best results than the default '100' setting.
    But as the S lenses distortion is rather low, it's not that easy to check.
    Should make a brick wall pic some day...
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    Re: Setting the right lens distortion correction

    Distortion indeed varies with distance and Lightroom does not take this into effect. I think that the only tool which corrects for that effect is Phocus (for Hasselblad H), but maybe dxo does the same.

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    Re: Setting the right lens distortion correction

    Hi guys. I'm an architecture and interior photographer and currently shoot with a Hasselblad. The Hasselblad/Phocus produce the best results of any camera/software combination I'm aware of. I am however wanting something a little more flexible especially for travel and thought the Leica S looked would provide a good solution but after testing the camera and lenses I haven't found any way to correct the complex distortion produced by its lenses. Capture One and DXO don't support the Leica S while Capture One and Adobe Camera Raw don't take distance information into account. DXO looks like it would be the only software that could properly correct the distortion IF it had profiles. So for the time being it looks like I'm stuck with the Hasselblad. Hoping someone comes up with a solution because the new 007 looks like a promising platform...

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    Re: Setting the right lens distortion correction

    I currently shoot with a H3D and have never noticed any distortion in a single shot taken in the last 10 years. Hasselblad have over 200,000 profiles/corrections for their range of lenses which take into account focal length, focus distance and aperture.

    The H3D needs a service costing $5000 so I've been shooting with a Canon 5DIII and Sony A7RII. I find distortion in most shots where the focus distance isn't infinity (almost all interior shoots) which is a problem given I shoot interiors for a living.

    I borrowed an SE with 24mm lens to test. Even with lens corrections applied, notice the bottom edge of the bench... moustache distortion consistent with the distortion charts for the lens. Not a great look for a $30,000 camera/lens combination!!!
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