>>3903010In any case, practically speaking, with 250D I'd set the ISO at 100 on your camera, with 500T at 200, and shoot without worrying about anything.
Don't tell anything to the lab, you let them develop normally.
Do that and see how you like the results. I think you'll be happy with them.
>As I understand film, over time, loses it's sensitivity so it gets "lower ISO" so if they are optimistic about the films ISO and this to me sounds like you're saying that they believe that their rating is correct and not lower. So, let's say I bought the film 2 years ago and haven't sent it back yet for development (I have some health issues that has made covid very dangerous for me so basically 0 photography) is it GOOD or BAD that I've OVERexposed their film by the 1 stop the recommend It's good.
About loss of sensitivity, this is not what I was referring to. Now that you mentioned it though, the general rule of thumb for *negative* film, is overexpose by a stop for every 10 years out of date. If you wanna play safe, a bit more.
This is *on top* of any other adjustment you'd do normally, like for instance overexposing half a stop (even with fresh film) because you like the look you get. In this case, after 10 years, you'd start with 1 stop overexposure to compensate for loss of sensitivity, and then on top of that you'd add another half stop (or whatever you usually do) to get the look you want.
What I was referring to with "optimistic manufacturers" is about B&W film.
Some manufacturers can give a higher speed as box speed (because for marketing it looks better to have 400 on the box than 200), than most people can practically get when using the usual developers.
So if you follow a box speed that is optimistic, and develop according to the instructions, you'll get loss of detail in the shadows and some graininess (those are the visible effects of slight underexposure).
Off the top of my head, Fomapan 400 is like that, for instance. Some others too.
