On the same camera body (Canon 1Ds MkII) at the same ISO setting (400) and with no filters attached, two different lenses give the same exposure time (0.4s) at very different apertures. The lenses and the apertures are:
- Canon 17-40mm L @ F/4
- Canon 28mm @ F/2.8
Given the differences between the apertures I would expect the exposure times to be different but they are the same. No filters (ND, polarizing etc) were used. How is this possible?
More data as per your request:
- The focal length of the 17-40 was 17 mm, even if through the zoom range the exposure was (almost) the same, including (of course) the value at 28 mm.
- The scene was entirely the same (a rather dark one, no bright spots) - no light change, no settings change etc. In fact, I saw this sporadically and I tried to reproduce it. So, the camera was steady, shot a frame at 17 mm, change the lens, shot another one at 28 mm with the prime.
- The camera was set up in average metering.
- Both lenses were used full open - at F/4 and F/2.8 respectivelly.
TIA for your feedback so far.