Scanning 4x5 on a Canon D2400F

[ADG]

Just to report my experiences with this scanner in the hope others may benefit and share their hints and tips.
1. As standard the film holder allows 4x5 to sag in it's natural curl and create netwons rings by touching the scanner glass, so I scan the film upside down and reverse in Photoshop.
2. As standard the scanner overexposes highlight detail, the histogram (in PS) shows a mountainside at the extreme right. I now lay a sheet of neutral density acetate (Lee filters ND 0.3 gel ref 209) on top of the transparency holder but not covering the 'do not cover' section that the scanner uses to calibrate itself, and the histogram tails off nicely into the bottom right corner and amazingly leaves the shadows intact. This is the biggest improvement by far and I am very pleased about it.
3. I have laid a sheet of black card over the glass that the film holder does not occupy as the internal finish of the scanner is white (why?) so this slightly reduces light bouncing around inside.
Hope this may help with other scanners too.

[Kirk Gittings]

Just curious. Why would a nuetral density filter alter the shape of a histogram since it adds density evenly to the whole negative?

By the way I have had some success with the sag problem by setting the sanner on its left side to take the weight off the center of the film. have had a noticeable bump in sharpness this way.

[Doug Dolde]

Also you might want to try a Gradient Fill Layer in Photoshop. This works quite well and you can adjust the blending percentage to control the effect.

[ADG]

Kirk, I really don't know why, but it does. I tested the theory with a small format transparency and the ND half of one of my camera ND grads to see what happened before ordering the sheet of gel.
I was fully expecting the histogram to shift left by the equivalent of one stop, but instead it compresses the range of tones into a smaller range. If I knew how to, I would post before & after screen grabs of the histograms.
If you have a ND filter and a suitable transparency could you try it ?
I think I may have got the scanning the film upside down idea from one of your posts.