Quote Originally Posted by RalphLambrecht View Post
yes, but it's a promise no filter supplier has been able to keep yet,
The Ilford set I had was very close when I tested it. At least as close as I could test with a 21 step wedge.

which midtone gray is supposedly to staying constant?
The Ilford set I tested the gray stripe on the step wedge exposure was somewhere near the geometric center of the grays visible. I did not measure the exact reflection density.

and second, is that always the right tone the exposure is judged by?
Well that is the tone you need to use to use the filter set correctly. If you try to judge exposure based on black, white or some other gray, you are not using the filter set properly as designed. I'd ignore criticism of a product what was used incorrectly.