Fri 08-Jun-12 02:16 AM | edited Fri 08-Jun-12 02:20 AM by nrothschild
>> You can get that effect by getting closer to the subject.
I already said that if you can control your working distance such that you can always fill the frame then f/2.8 is f/2.8 at any focal length. In that case you just don't need a lot of light gathering power because you don't need focal length.
And if you can shoot a warbler with a 70-200/2.8 by walking up to within 5 feet of it, you are good to go. If Perrone can just walk out on the playing field with an f/2.8 then he doesn't need to worry about LGP either.
>> You can get that effect by using a longer focal length...
If you increase focal length without increasing the front element, you reduce focal ratio. That's what TC's do.
If you pop a TC on a lens you will NOT reduce noise because you did not increase your light gathering power. If that is all you do, you will add obvious noise because you will have to boost ISO 1 stop to avoid reducing shutter speed and you just lost a stop of focal ratio. You pick up the stop on the back end with less magnification. A net push.
If you want to reduce noise while increasing focal length you must make the glass bigger. If you want to go from 200/2.8 to 300/2.8 the glass gets bigger. And etc.
I have said repeatedly that LGP only matters when you cannot close your distance and you have too much noise. You may have too much noise because you are using a TC and the resulting focal ratio is too small. Get bigger glass to get to that focal length without a TC.
If your focal length is too short and therefore your resulting image too small, then adding a TC is a push. Same noise, assuming the TC does not require you to stop down even more, and in that case you are a net loser.
If you want to make the focal length longer without making the focal ratio smaller, then you have make the front element bigger to maintain that fast speed.
Everything in the context of Perrone's thread here is predicated on him shooting a sport from a fixed distance he cannot control, and with low light considerations. In that case, bigger glass and bigger sensors always win. They reduce noise. Individually or together. But to make a bigger sensor reduce noise you need the focal length to go with it, and thus you need bigger glass
And so on. No matter how you look at it, if you have too much noise LGP rules.
>> 500mm or 600mm the total amount of light across the frame is the same as long as you are at f/4.
If LGP doesn't rule, then why do people spend extra for a 600/4 - and haul the extra 4-5 pounds around - if they can do the same with a 500/4 and just get closer? What makes a 600/4 better? It's the 6" of glass on the front, verse the 5" of the 500.
For that matter, if only focal ratio mattered, then a 300/2.8 would be even better. It's a stop faster, cheaper and lighter. You're a 3 time winner. Why are we not birding with 300/2.8's?
(I know the answer because I upgraded a 300/2.8 to a 500/4)
For that matter, why not use a 70-200? It's f/2.8 too, and if only focal ratio matters it is superior to a 600/4.
I'm trying to get you to think this through
>> What you seem to be saying is that more of the light that is gathered is on your subject rather than wasted on the background.
That is what LGP is all about. If warblers grew on trees we would shoot them with macro lenses just like pine cones