In article EThMi.274464$fJ5.109835@pd7urf1no,
"jim wilson" wrote:

True, of course. I spoke only of the amount of light passed by the lens
aperature without reference to how long that light is allowed to hit the
film or sensor. Both settings, as you say, make up "exposure". If the
correct exposure for a photo is 1/125 at F16, it doesn't matter whether the
lens is 50 mm or 1000 mm, set both to F16 and the exposure is correct-but
don't hand hold the 1000 mm lens at that slow a speed. 8)
jim

That's right, Jim. My foggy brain is clearing up now - the 1/focal
length rule refers to the longest exposure you can use without a camera
support.

Dave