Hi there, I am pretty new to photography (or rather very new to raw-processing) though aware of the lensfun library for quiet some time now. Anyway, I recently bought a Sony Alpha 6300 (also named ILCE-6300) with a Kit-Lens which is found in lensfun as: Sony, E 16-50mm f/3.5-5.6 OSS PZ. Today when comparing the JPEG produced by my camera with the lensfun-corrected RAW result I noticed quite different results and I'm wondering if you're interested in my observations and if the lens-correction is doing something wrong.
Vignetting At 16mm and 17mm the Lens has pretty strong vignetting. You can see that here: https://jeanbruenn.info/lf_original.jpg and here: At 18mm the "strong" vignetting disappears. However, as soon as I do apply lens-correction (I do use darktable for that) I believe (it's difficult to spot/see on my screen and it's mostly noticable on thumbnails) that there is some sort of "light" vignetting as soon as I do apply the lens correction. Take the following downsized photo for example (https://jeanbruenn.info/thumb.jpg), all four corners show a white dust/mist just like in a vignette-effect. You'll get it more visible if you open that photo and play around with the contrast slider so that the white from the borders is increased: The same in the following two Pictures (uncorrected: https://jeanbruenn.info/lf_original2.jpg, corrected: https://jeanbruenn.info/light_vignette.jpg) Cropfactor This made me check the JPEG of the camera and compare it with the lens-corrected RAW one. At first I've been pretty much impressed: JPEG from my Camera: 6000x3376 RAW lensfun corrected: 6048x4024 Which means the camera (is probably aware of the issues with the lens and) crops a massive amount of 648px in width and 48px in height. However. This might as well be some sort of misconfiguration of me (since I told my camera to take photos in 16:9 when I took those photos - Going to check with the 3:2 setting later / tomorrow). Further correction Now it's getting interesting and difficult as well. With the above in mind, I did the following experiment: I opened the cameras JPEG in gimp, I applied lens-correction to the RAW variant of this Picture, exported it with darktable and opened it in GIMP as well - Now I took that, overlayed it as new layer on the cameras JPEG and I did set opacity to 50%. It seems the camera crops with different values from left and right - happily I used a picture which has a small duck in the middle. So I moved the layer until it exactly matched the duck. In theory everything else in the photo should match as well now. However, the more you slide to the right, left, bottom or top, the more you can see ghosting while it is fine in the middle. Which pretty much means (assuming that the camera is correct) that the lensfun corrected image is not correctly distorting/de-distorting (whats the term I search for?)/correcting the photo. You can see that, if you zoom in and move from the middle to the borders: https://jeanbruenn.info/overlayed.jpg https://jeanbruenn.info/camera.jpg https://jeanbruenn.info/lensfun-export.jpg This is even better to see with portrait-like photos of persons. So, are my findings correct, that the parameters for the lens in lensfun are incorrect? Or is it a combination of the Alpha 6300 with that specific Kit lens? I already tried another lens which does not have the strong vignetting (though it's 50mm-210mm) and is also not so much "corrected" by lensfun. So I assume it is not a problem with my cam. Not sure though. Assuming that my findings are correct, is there anything I can provide to get a more accurate correction for that specific lens (or camera/lens-combo)? I do not own any calibration equipment, though :( By the way, I believe the same lens is used for previous camera models like the Alpha 6000. Would be interesting to know if those show the same behavior (with the same lense) Jean
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