If FF works, it works well. But Lightroom seems to have a mind of its own when it comes to whether or not it will ‘find’ the calibration image, and then sometimes it processes it, but with no actual corrections made
Yes, flat field correction is extremely unreliable, sometimes it works, sometimes it doesn’t in my experience. It will not work on scenes that are relatively flat, like an open field landscape, for instance, it doesn’t know which image is the calibration file. Also, the fact that a duplicate file needs to be created every time means large amounts of storage space.
I am beginning to think the falloff pattern is highly dependent on the lens being used. As an experiment, I wanted to try a different macro lens with my Fuji XT-5 to see if I got better, or at least different, results.
What I found is the falloff pattern is completely different with the other lens. This is going from the Laowa 65mm to the Fuji XF 80mm. Different focal length of course, but if the falloff was dependent on the light source specifically, I would have expected to see a similar elliptical pattern to the one in my video above.
Instead it looks like this.
So it doesn’t see to be as straightforward as light bending around the edges of the film mask on the carrier, or the falloff pattern being dependent on the light source itself, the lens is making a significant contribution. Using Lightroom’s built-in vignetting correction profile for the Fuji XF 80mm has little to no effect.
The lens vignette and the panel falloff may work together to form that image, but they are separate variables and should be remedied independently.
I recently was lobbying for Adobe to improve flat field correction on the Lightroom forum, provided examples of the issues I was experiencing with FFC was not working on low contrast images. Happy to report they patched it in the most recent Lightroom Classic update 14.1.1.
I was able to do a batch of corrections, but only if the calibration frame was first in the series (using it as the last caused issues as it tried to use the first frame for calibration). It also corrected applied FFC to low contrast images, which it used to skip entirely.
So it seems like FFC has become a viable option again, if you don’t mind the extra storage space using it requires.
I just had a thought, are you using flat field correction along with the built in lens corrections in Lightroom? Using it with FF calibration will cause issues.
Its also my understanding that FF correction is for correcting the lens by removing unevenness in the imaging path by giving the software a reference image and won’t work well if the source isn’t even. Commonly done in astro photography to even out light fall off in telescopes.
Personally, I set the light source as close to the lens as possible to put any source unevenness out of the equation as much as possible. Take the reference image and then run the correction.
*edited the first sentence for clarity.
I always disable the lens corrections. Yes, the calibration image needs to be a blank frame to work. The issue is Lightroom is supposed to detect which frame is the calibration frame, and it often gets it wrong and uses a different frame. It also used to skip corrections on low contrast frames. This was fixed to some extent with the recent patch, but it seems the position of the calibration frame is important if you are doing a group of images as a batch. As I said, placing the frame at the end resulted in errors (when correcting a batch of 37 images from a 35mm roll), but placing it at the front worked just fine. If you do the FFC for each frame one by one, it doesn’t seem to cause a problem either, but the calibration frame needs to be moved before the image to be corrected for each FFC and it’s pretty time consuming.
Gotcha.
I usually only do a small amount of 120 (1 roll or so) or some 4x5 negatives at any one time so the issue may have been masked by my use case.
I have seen some weird things though so I’ve deleted images and re-imported things from the card.