Originally posted by stevebrot Perhaps not completely meaningless, but close to it. I won't go into the technical details, but quite a bit of the equivalence stuff is dependent upon a series of sketchy assumptions*. The fact that you are not sure about determining FF-MF equivalence is a good indication. Another good indication would be the lack of historic obsession about such. I have been doing film photography for a number of decades and nobody (I do believe that means zero) is particularly concerned with calculating the equivalence (in stops or any other units <rolls eyes>) between 645 system lenses coupled with available cameras and films and 6x7, 35mm, 4x5, or 8x10 with same. Why? Because it is not very meaningful.
What is meaningful is whether available optics are fast enough for adequate DOF/focus control while addressing practical considerations such as appropriate shutter speed, focus system, available lighting options, available capture media, size, and weight. Thankfully, these details have been worked out through many years of field experience. What is on the shelf to buy generally represents what works.
Steve
* Occam's Razor: "That proposition requiring the least number of assumptions has the highest probability of being correct."
"I'm not sure" only because I don't have time nor will to do the math... but it's only a matter of area vs area. I.e. I'm not sure of the exact number, not of the fact that there's a difference - assuming same underliying tech of course, CCD vs CCD, CMOS vs CMOS etc.
And no I still don't believe it's irrelevant; and while being a fan of Occam's Razor myself, I don't think it applies here.
However the OP point still stands, maybe you don't lose a stop and a half because you make up part of it with the larger sensor, but at least half a stop, yes.
Bottom line for me and my shooting: MF is too expensive for generalistic use, for that we have FF, APS-C, mu43 etc. it's only a matter of price, portability, "quality" etc.
I couldn't stand not being able to choose from so many different lenses, each with its own characteristics, even in the same focal length range. With MF it's those few lenses and they are way too expensive to afford duplicates...