Tried the radial filter, which made a big difference, even with a closed aperture.
This is how I made the filter/mask
- Display a reduced view of a blank capture of the backlight (Kaiser Plano in my case)
- Draw a radial mask, circular in my case, that extends from corner to corner
- Reduce exposure until the center and corner brightnesses are about the same
and let the histogram guide you: the narrower, the better - Adjust mask feathering until brightness is about the same from center to corner
and let the histogram guide you: the narrower, the better - Adjust overall mask size if that further improves evenness
- Close the mask tool and adjust global exposure to compensate the darkening you got from the local adjustment (the gradient mask) you just made
- Save as a new preset (only check exposure and mask items)
Notes:
The Plano extended well over the field of view of the lens which was set to capture 1:1.
For perfect masking, you’d probably run through steps 3 to 6 more than once.
For perfect masking, you’d have to create a filter for each imaging ratio (1:1, 2:1,…) and f-stop.
For higher f-stop numbers, I had to adjust feathering mostly and correct exposures slightly.
Use Virtual copies for experiments.
Make the Lr background about the same tone as the image.
Before - After
Caveat: Lens falloff is usually not linear like a radial filter gradient. Nevertheless, this way to correct falloff suits many cases anyways.