As part of testing a new developer I've created (in "Progress on XTOL-concentrate" thread), I've been testing and plotting all films made by the big three makers. T-Max 400 has this interesting curve:
It's shaped like a boomerang, and that will cause highlights to block up sooner. If you're spending much time burning-in your highlights with T-Max 400, this might be why. For comparison, here are curves for HP5+:
Once past the toe, HP5+ marches in a straight line like a soldier. This also shows that my own test equipment and methods aren't producing that boomerang curve. I saw this issue with T-Max 400 a few months ago, but I blamed my own testing. But results with other films show that my tests are okay. Interestingly, Tri-X also makes a boomerang:
But the boomerang for Tri-X is facing up instead of down, and the change in angle is small. It'll give you a bit of compression (compensation) in the highlights.
T-Max 400 worries me. In a prior posting, PE said this means that Kodak is having trouble blending emulsions correctly. I think T-Max 400 has two emulsions. Hold a piece of paper against the monitor to use as a straightedge, and you'll see that the curve consists of two straight lines. I suspect their slopes are supposed to be the same.