> So if you had an exposure time of 1/500 at f/2.8, your f/22 exposure could be 1/250 or so, depending on how quickly the blades open/close.
The other way. Times with f/22 are faster. The shutter opens a bit, which is sufficient for f/22 and then opens to cover the f/2.8 which takes time.
Actually, the previous poster was correct, if you reason it out. His username, Mamiya_Repair, gives a hint why he would be. I don't have time to write out the full explanation, as I believe it to be (I hope someone will correct me if I'm wrong), but to boil it down, in a Hasselblad lens, the shutter and the aperture are
two separate mechanisms. The shutter has
nothing to do with the size of the aperture.
And no matter
what aperture you shoot at, the shutter blades open
all the way. The aperture mechanism, which is separate from the shutter, determines the size of the opening the light passes through as the shutter blades are open.
When you fire a leaf shutter, the center bit is the first part that opens, and it's also the very last part that closes down--it is open during
the entire shutter cycle. So if you're shooting at a small aperture, because of shutter inefficiency, the center part has to "wait" for the shutter blades to open completely (even though, as you pointed out, they wouldn't
need to for, say, F22, but the design of the shutter
requires them to open all the way) and then close back down again. So after the shutter blades have passed the diameter of the F22 aperture when opening, and before they come back to the point they are closing
it back down, "extra" light is being let in--the exposure time is lengthened.
If you're shooting at F2.8, because it does take time for the shutter blades to open to the full width of the aperture, but then immediately they start closing down again from the edge,
effectively the exposure of the entire wide-open aperture
as a whole is approximately 1/500 second. The entire shutter cycle lasts a fair bit longer than 1/500 second (which is why the center portion, corresponding to the F22 aperture and open nearly throughout the shutter cycle, is open
longer than 1/500 of a second), but because the periphery when shooting at 2.8 is "deprived" of light because it's the last to be uncovered and the first to be recovered, the
effective exposure is less than the time of the entire cycle, and should hopefully correspond to the amount of exposure you'd get from a perfectly efficient shutter that uncovered the entire F2.8 aperture diameter instantaneously, and just as instantaneously closed it completely 1/500 of a second later.
I know it's counterintuitive on the face of it that a larger aperture should have a shorter exposure time in this scenario. But because they are separate mechanisms, because of how leaf shutters work, and because the shutter opens all the way on every exposure (not just the minimum distance required), no matter what you've set the aperture to, it actually works out that way.
That's my explanation, anyway!