Yeah I thought it was all a bunch of huey, until I got an 8x10 print back from the lab that clearly showed the negative had "popped: warped in the enlarger from heat and gone out of focus. He reprinted it with a glass neg holder and the image didn't change.

That's when I knew there was some truth to film flatness. It was shot with an XLSW (47mm SA) at f8

hey bigglassman

will the film flatness its just what you get some good & some not so good

But you can look & see by putting in a roll of junk film get it ready to shot
take out the drakslide & look ! NOW if it looks like that the film touckes
tight all the way around the film gate you should be OK! if it don't then a
know that you mite have some problems!! But that can some times it can
be fixed. Some have added a felted backing on the presser plate to take
care of it . ?? I have never tryed this but have been told that it works but
it makes your film a bit roll harder !!

Banjo