Flat-Field and/or Falloff Correction

Hi Nate, is this possible at all? Lightroom’s implementation is so hard to use and seems too smart for it’s own good. Flat-field curvature is likely a very complex algorithm but a simple light calibration like what Filmlab (see here) does would be a very useful feature. A correction that isolates the relationship between the light source and the capture device would be extremely useful to ensure evenness pre-conversion.

I don’t know if I’m alone with all the strange color shifts on some edges with certain films, regardless of what I do. It’s probably my camera sensor and lens at this point and they’re not exactly very easy to replace or low-end for that matter.

Hi @eslc,

Are you saying you have tried Lightroom’s built-in Flat Field correction, and did not get good results? I’m not sure why that would be, as I’ve had good results with it. The nice thing about Lightroom’s built-in Flat Field correction is that the resulting corrected files are still RAW, which would quite tricky to implement outside of Lightroom. It may be possible to use the layers masks to make a corrective layer on the RAW, or I could possible have an option during export to use a separate photo as as a mask.

If you share more about your setup, it’s possible that we can fix this at the root cause. Somewhere along the way, you are not getting even light on the negative… either due to too small a mask on the light source (causing a shadow before it hits negative), too much direct light hitting your camera lens (caused by not masking out sprocket holes or direct light), or smudges on your light-table/diffusion-layer/etc.

-Nate

Hi @nate,

Yeah, LR’s built-in Flat Field Correction is wonky for me. I can’t seem to get it to work reliably. Some images catch a ghost of one image in between the selection and it seems random. Sometimes, the batch process would only turn out a fraction of the whole selection. Putting the calibration image in front or at the very end doesn’t change the result. During my last try, I made sure not to move the scanning rig at all and all the issues I mentioned popped up. Am I possibly doing something wrong?

It’s possibly the sprocket holes but it’s also strange if they are the cause because the color shift comes from only one side of the frame and not from the top or bottom where the holes are. I’ve tried overexposing film and that has mitigated the issues.

I can adjust the WB to make the shift disappear in the posted image as you suggest but this tactic gets a bit disruptive for certain images because it’s isolated to one side. This image had the sprocket holes exposed.

The trend I notice is that it happens more often with both extremes in terms of density. It happens a lot with blue skies and or images with darker edges.

I’m using an A7RIV with an unfiltered FE 90mm Macro as the capture device. The light source is a Negative Supply 99 CRI 4x5 Light with a Basic 35mm holder. The mask is a dense anti-ESD foam. Captures are done in complete darkness at f/8 and the shutter speed is usually slow, 1/6 to 1 second maximum. I have also leveled the setup as much as I can. By the way, the issues pop up with the Essential Film Holder with the Viltrox L116T as well.

I read somewhere that there could be an issue with the camera and lens combo but can’t remember where exactly.

The thing is I don’t seem to get visible issues with positives, even with sprocket holes exposed. I’ve also had clean negative conversions with sprocket holes exposed. For B&W, nothing seems too distracting.

There is definitely some sort of unevenness in play but it is mindboggling. It’s why I thought a falloff correction feature would be useful but it’s a backup in case all else fails.

Any help would be appreciated.

Please post an original RAW file or two. Use a sharing service for ease of use.

We can then try to see what we can do…

Flatness of field refers to the lens’s ability to focus on a flat plane, and there is nothing you can do about it in a software adjustment; you would have to focus in multiple points in multiple shots and combine them. Light fall-off is totally different and there are adjustments in LR (I’m told) and Capture One (my software) that compensate for uneven lighting to a reasonable degree.

Just a thought,

Have you tried different f stops like f4, f5.6, just to rule it out? Does it have any effect ?

Also is film flatness an issue?

FW