Since I just got spanked* on another forum, I thought I would post the question here.
In a discussion on F/1.4 lenses, the brightness "limit" at f 2.8 came up. I quoted Ken Rockwell from here:http://www.kenrockwell.com/nikon/d70perf.htm#finder
And was told this was hogwash:
"Stuff and nonsense! How would the viewfinders do that, by magic?
The only way would be if open-aperture metering was "limited" to the f/2.8 stop, like a rev-limiter on an engine. And for all I know, maybe some cameras do this.
But in the spirit of empiricism, I actually DID perform my own experiments...I happen to have two identical camera bodies here, and two lenses of very close to the same focal length but of more than a stop difference in maximum aperture (31mm f/1.8 and 35mm f/2.
And, of course, the faster lens shows a brighter viewfinder image and less d.o.f. in a careful comparison. (Although I felt a little sheepish actually running the experiment, like when your friend is looking up and says, "how about that, someone wrote 'gullible' on the ceiling," and you look up at the ceiling.)
I do NOT want to pick a fight with your expert, which is why I elided his name, but that's just another eye-rolling internet myth as far as I'm concerned. Of course, maybe he's using a Whapoflex and his camera works differently than mine--I can't speak to that."
Any thoughts, Bob?
*Here is where I was spanked:http://theonlinephotographer.typepad.com/the_online_photographer/2011/04/internet-canard.html#comments