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Hi group, Well I was always wondering: Why don't lenses provide the F stop which exactly corresponds to the light actually hitting the film emulsion or sensor (not accounting for lens flare and other random factors, just the glass inside the lens)? So in reality: if I get an F stop value from, say, a light meter, I most likely will get it in T stop. Otherwise the "exposure triangle" would make no sense (to me that is). Looks like some lenses are reducing as much as one stop while others perhaps a third of a stop. There is some information for some lenses regarding the actual T-stop, but many don't come with that information - and even with that information: what to do? Now add certain filters and you're into some serious math.... The only thing that remains the same (F stop/T stop) is of course the depth-of-field/focus. Fully automatic digital cameras with 100% matching lenses (or built-in ones) most likely take all that into account (to varying degrees of success IMHO). But what about using different lenses with no electronics and a 100% manual exposure? With film, once it's in the camera (and you don't have a variable shutter angle) your only way(s) to control exposure is/are lighting, filters and F stop. Please let me know how you go about the F stop vs. T stop issue and avoid under exposure. As always: any reply highly appreciated. Christian