Originally posted by starbase218 My wants are different, but that wasn't really my point. My point is, once you put a lens on a smaller sensor camera than the one it was intended for, you ARE losing f-stops relative to that camera. It's math, and it's caused by all the light falling not on the sensor, but beside it. This has nothing to do with different needs, it has to do with the fact that if you say your 70-300 becomes equivalent to a 330-1400, you can't say it still behaves as if it were, what, an f/4-5.6? Why? Because at 1400mm, the lens would need to be at least 1400/5.6 = 250mm in diameter, or 25cm, if it were to behave like a 1400/5.6. But instead, it's still 300/5.6 = about 54mm. So, taking that aperture and the new equivalent focal length of 1400mm gives us an equivalent f-stop of 1400/54 = f/26, give or take.
You say it's different from using a teleconverter, while it's the exact same thing.
Check out this video if you want to know more about it:
http://www.youtube.com/watch?v=DtDotqLx6nA I'm a mathematician by education, and I have taught mathematics at the college level, but I'm not interested in some guy talking on youtube about theory. I have always been more interested in practice than in theory. I can read and comprehend the theory for myself, but my actual interest is in practical photography.
What I know from practical experience is the following: I can use a $200 70-300mm lens on a $400 Q-S1 and get good solid pictures of birds in my backyard; yes, maybe I use a setting of f/4 and the camera sees the light that would normally go with something like f/8 (*) like a 2X converter would; my experience is that I get plenty of light to take a reasonable picture; I'm not losing anything like the amount of light that your theory predicts, and it gives me much better pictures than the 2X converter would.
Another option would be to buy a $750 K-3 and a $1050 150-500mm lens (total cost $1800 compared to $600 for the Q package),then crop the resulting picture by a factor of 3 (4.7/1.5) in each dimension, turning my $1800 system into a 3MP system; perhaps the superior K-3 system would produce 3MP crops as good as the 12MP images produced by the Q, but I'm not sure I would want to bet my $1800 on it.
Then, once I'm not taking birding pictures, I can replace the adapted zoom lens on the Q with a 01 prime lens, put the whole thing in my pocket, and go on with my life.
(*) I actually did this experiment in my backyard a few minutes ago.
I aimed my Q7 with the adapted zoom at a spot in my garden with the lens set at f/4 and determined what shutter speed was needed;
then I mounted my 06 lens, set the camera to Tv mode, set the shutter speed to the speed recorded above, and then walked to the point where the same area filled the LCD.
The camera was setting the aperture to 7.1.