Yeah, some of those preset I previously created would sometimes make the corners too dark or would not cover the image correctly. With FFC it’s a one click solution to every roll you scan no matter the variation you get in the vignette of your scan from roll to roll.
My camera settings always stay the same, but I set up and take down my copy stand every time I scan. So I would always end up with varying results of how the vignette on the scan looks from one day to another.
NLP is built to analyse an image and every change, e.g. of a crop changes the source of the analysis. Sometimes, the difference between conversions with different crops look similar, other times, they don’t. This adaptive approach has its benefits and downsides. One benefit is, that you can e.g. crop off a negative’s larger areas that are either too thin or too dense.
I mostly don’t crop images before converting, but set border buffer to between 15% and 25% instead. This usually works, but some negatives require extra care.
Thank you for your exhaustive investigations into sharpness, FFC and exposure.
At the risk of sounding pedantic I fear you may be misunderstanding what I said about digital exposure.
First, digital exposure is radically different to exposure for film so I’m a little unsure as to what you meant when you described ‘correct’ exposure in your scans. It is not the adding or subtracting of a stop or two either way and judging the displayed appearance.
Second, it is no surprise at all that your Aperture priority exposure matched the Manual exposure for the same frames. The meter is programmed to read the same values for both. However, whether that exposure is ‘correct’ is altogether another matter. If the highlight values are hard up against the right hand side of the histogram then indeed that exposure could be deemed correct. Anything less than that however, amounts to under-exposure, no matter how it ‘looks’. EV compensation should be applied until the histogram (as opposed to the appearance) is where it should be. Correct digital exposure (gathering the maximum amount of data short of clipping the highest important highlights) frequently looks pretty bad in the back of the camera and when displayed in software…too bright by far. This nevertheless is the correct exposure. How it looks to the human observer is then a matter of taste and is achieved by adjusting the (misnamed) ‘exposure’ slider in Lightroom et al. This is in fact a brightness or gain slider and has absolutely nothing to do with exposure.
Nate’s idea of adjusting exposure, using the light source itself, to just short of clipping is a practical implementation of the above but only gives a baseline exposure which will prevent clipping universally but will only work well with reasonably well exposed negatives.
Adjusting exposure in the way described often need not be necessary on a frame by frame basis. If the whole roll is of the same subject and has been exposed fairly uniformly then the EV adjustment for one representative frame can safely be applied to the whole roll. If however, the roll has frames of different subjects, exposed differently in varying light conditions at different times then all bets are off and it’s back to a frame by frame assessment.
If I have misunderstood your process please ignore all of the above!
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Just a general remark on flat field correction.
Taking one reference at the beginning or end of a series of captures implies, that FFC must be applied as the very first step.
Everything else like flipping, orientation, cropping etc. can be done later. Flip and crop are two actions that Lightroom doesn’t track and if you e.g. flipped the image, but not the reference, FFC will probably do no good. 
I’ve taken a single frame meant for FFC that’s at the end of all of my scans, but every time without fail whether I select it and just one scanned negative, or the whole deal, LrC insists on telling me the first or last frame must be a flat-field calibration frame. I’ve tried some of the suggestions above with removing the scans and re-importing, backing up the catalog, etc.
Not sure why it’s fighting me like this, but this seems to be an issue that isn’t solely confined to my own experiences with this.
I had the same issue before. Then I took a series of shots with a trailing reference that was exposed to the right. From then on, FFC worked every time.
I’ll have to give that a shot. B&W is usually fine, but if I can rid myself of the vignette that causes bright edges then I’d be happy to remove that from my workflow. Being able to kill off the orange haze when doing color is where I’m really wanting to be! It’s one of the reasons I haven’t been scanning color negative.
Negative Lab Pro removes the mask, no need to handle it manually. I did that for a while, but it is tedious in comparison to using NLP.
Haven’t tried FFC to remove the mask. FF corrections were quite subtle in my tests and I’ be happy to see if it can do more substantial stuff like removing the orange mask.
Hmm, okay, might be a case of PEBKAC over here in terms of my settings as when I was doing conversions of my Fuji Color 400 scans, I couldn’t get rid of the haze.
I’ll try again this evening when I get home from work. As sharp as the Minolta MD 50/3.5 Macro and bellows combo I use is, there’s definitely still some aggressive vignetting. It’s also one of the reasons I’ve not attempted to scan any medium format frames as I’d want to stitch for maximum effect.