I have a Leica Mini Zoom and Nikon One Touch and have a Portra Seller Lab at Street.
All other 100 ASA Films Fuji or Kodak comes normal but Portras comes 4 stop darker.
Is there a problem at high heat Lab or my cameras ?
How do you know that the films are 4 stops under? You do that by looking at or measure the negatives with a densitometer or do you judge that by looking at the prints? Looking at the prints can be very misleading.
Also excess heat tend to get the film denser (like overexposure) not thinner but for the most part it won't except change color balance.
How did you determine that there was a 4 f/stop difference?
What ISO setting did you use for the Portra film?
If you shoot the same subject on a bright sunny day and manually set all your cameras to the same exposure of f/16 at 1/125th second, will all the negatives look the same?
There is a lot of room for operator interpretation during the scanning or back in the days printing process. So the scan or print not to your liking is very much because of how the lab does it. But the 4 stops? 4 stops underexposure on color negative film you end up with almost nothing on the film.
All black , only sunlighted scans means something. I gave 7 different rolls at different times and this roll ended black.
I will walk there under July heat again.