Ste_S
Member
I have a light meter app in my smartphone too Thomas, but I don't use it because it underexposes by about two stops as well, so it's about as much use as a one-legged man in an ass-kicking contest. I suggest you buy yourself a modern digital light meter made by Sekonic or Gossen.
I shoot with an iPhone app (myLightMeter or ASLightMeter) to meter for my meter-less medium format cameras and have had zero issues with exposure.
They're normally pretty good as long as you 'spot' meter for the shadows for C41/B&W