I shoot with a 500mm and 300mm lens. The 500mm lens is what I use when shooting shore birds, open land birds, or any birds flying. So about 85-90% of all my shots are with the 500 mm lens. But, when it comes to low light close quarter shooting I ditch the 500mm without a thought.
Shooting in the jungle under the canopy in Thailand is a challenge. After lugging in a tripod, a blind, a stool to sit on, and my big glass. I was getting fed up. Backpacking in the jungle with all that gear is a night mare. About half way threw the day I would be tripping over vines, my tripod and bags were constantly getting caught in the brush and shrubs. Just a frigging nightmare.
The 300 F/2.8 changed all of that. First AF with a 2.8 lens in very low light is a god send. Much more accurate and faster than F/4.0. You would not think there would be that much difference but believe me there is.
No more tripod. The IS on the 300 II rocks. Mono-pod only no matter what shutter speed. No more stool to sit on. I sit on the ground or just squat down if need be. It is so small and light! No more back pack to carry the lens. It sits on my side ready. I usually carry the mono-pod strapped to my left wrist.
As far as a blind? Usually I carry a camouflaged piece of material to throw over me and the lens if need be.
Is the 300 II sharp enough and fast enought to keep up with the 500mm lens? YES it earns it's keep and then some. You need AF to be fast and accurate The 300 is faster and more accurate in low light than my 500mm lens. You need to be able to move and shoot in a hurry. The 500mm lens is way to big and bulky.
This first shot is with the 500mm lens. I set up my hide in the middle of a stream to be able to get the shot. Shooting at F/4.0 is a handicap. I had to find a place with some light!. Still verrry dark. Next I had to lug in all the gear to the location.. I was cussing and sweating by the time I got there... And I am not kidding.
Then had to unpack the lens, hide, tripod and set up.
I did not have to find a location to set up. Actually I climbed a small hill and found the Pitta, dropped down with the 300 on a mono-pod, Threw a cloth blind over me, and the lens. With in 30 minutes I had 3 different species.
And was on my way to the next adventure! And in good spirits, No cursing, no swearing, no sweating profusely. No tripping over myself and everything else.
Just a joy to use! And it out performs the 500mm lens hands down. No contest IMO.
Comming in from this Pittia shot with the 300mm lens I was crossing a stream and an Asian Black bear decided he wanted to cross also. About 10 meters away. Only there for a few seconds. The 300 got three shots before he was gone. If I would of had the 500mm I would still be swearing and kicking myself for bringing it into the jungle with me... :)