This is just a short review giving my opinion on how well this lens performs in the real world. Having owned the EF 300mm f2.8L IS USM for 5 years and having been really pleased with its all round performance I decided to upgrade.
Similar in appearance to its predecessor the most noticeable change is the tripod mount which is now integrated and not removeable like the old version. This has resulted in much smoother and more positive rotation of the lens when mounted on a tripod. However most of the other major changes are internal and include completely redesigned optics with improved coatings, faster and more accurate AF system and improved image stabilization which is now 4 stops instead of 2. A third IS mode has also been added to assist when switching between subjects when the IS is only activated during exposure. The lens is also 200g lighter.
I will only comment on the three issues that are important to me as a wildlife photogrpher.
Perhaps the least important for me is the IS as it is rare for me to hand hold this lens and if I do it is for birds in flight when I always switch the IS off (improves speed and accuracy of the AF system). If you think about it when panning with a bird in flight, the panning action negates any up and down movement. So for me the only time IS for birds in flight when hand holding the lens might assist is when the bird is flying directly at you. I have however used the IS mode on a number of occasions when working in low light on soft ground with my tripod and have shot many super sharp images at 1/15 which would not have been possible without a 4 stop IS.
The improvement to the AF system is quite noticeable particulary when using extenders. I must say that I have not noticed much improvement in speed and accuracy when using just the prime lens but when using the new mkIII extenders on my EOS 1D Mk1V the improvement is quite marked especially with the mkIII x2 extender. When using the the latter combination I would say that my success rate of birds in flight has improved greatly.
Optically I have noticed very little improvement when using the prime lens or with the x1.4 extender attached. A good test however for any lens is when you attach a matched x2 extender. No lens is perfect and with a x2 extender you are doubling any slight imperfections and with this lens the results are excellent and althought the improvements over the old lens are not massive they are marked and easily visble.
The below image was taken using a Canon 1D Mk 1V plus EF 300mm f2.8L IS II USM lens with a x2 MkIII extender attached. It was taken in flat overcast lighting to give as true a representation of the lens sharpness as possible. Due to the low light I had to use iso 1000 (not the best for sharpness) but I feel that all these factors have helped to illustrate how good this lens is even when the conditions are less than ideal.
Canon 1D Mk1V – EF 300mm f2.8L IS II USM plus x2 MkIII ext.iso 1000 f8 1/250
Same image as above only a small section shown at actual pixels.
I cannot recommend this lens highly enough, I am really pleased with its all round performance. My only two negatives are what is for me a completely useless expensive hard carry case (please canon can we have a soft case similar to those Nikon owners have) and the price.
If you are considering purchasing this len may I suggest you visit my preferred Canon main dealer Park Cameras, I have been a customer of theirs for well over 25 years