I'm a little embarrassed to say that until today, I've never tried shooting using the "Sunny 16" rule, and I figured it was high time to try it out; especially since, in the coming weeks, I'll be doing some film photography using a camera with no light meter.
For my first attempt, I used my old Pentax *ist DL and Pentax-F35-70f/3.5-4.5, since that was the camera immediately to hand.
It's a very bright, sunny day here, with cloudless skies... perhaps just the tiniest hint of haze, but really nothing to speak of. In terms of UK weather, I'd say it's about as good as we ever get. The time of my test was 1pm in the afternoon, with the sun not far past its peak. On that basis, I understand that at ISO 200 (the *ist DL's base ISO) and the lens set to f/16, a shutter speed of 1/200s should give more-or-less accurate exposure...
But it isn't. I'm seeing about one stop under-exposure. Indeed, if I shoot at f/11, exposure is pretty much spot-on.
What gives? Is this an inaccuracy in the camera's supposed ISO 200 sensitivity? Or perhaps f/16 on my F35-70 isn't actually f/16?
I vaguely recall a post some time ago - I think, perhaps, by @stevebrot - that mentioned how the "Sunny 16" rule doesn't quite work the same as you move further away from the equator. That might be a false memory, but if not, I'm wondering if the one stop difference I'm seeing could be due to that?
I intend to repeat the tests with other lenses and bodies, but won't have a chance to do so today, as we've family guests arriving later this afternoon and I have too many non-photography chores to address
UPDATE: I have an incident light meter app on my smartphone that works very well and is pretty accurate. It's giving almost identical exposure results to the *ist DL and F35-70. For ISO 200 and f/16, it's reporting a shutter speed of 1/80s, and changing aperture to f/11 gives shutter speed as 1/160s (close enough to 1/200s). So maybe the very, very slight haze is having more of an effect than I give it credit for? Questions, questions...
Any insight and/or advice would be much appreciated. Thanks
Last edited by BigMackCam; 09-07-2021 at 06:37 AM.