Thinking About a 300mm Lens

I am thinking about possibly jumping back into the lens wars.

After using a Canon 400mm f/5.6L for birds and longing for a 500mm f/4L IS which I just couldn't seem to make happen, I made a move to macro, flowers and other wildlife and have been spending more time in the past six months or so photographing nature other than birds and enjoying it immensely.

This got me to thinking. I have the 70-200 f/2.8L IS and the 400 mentioned above. I started thinking about a 300mm for flowers, butterflies and other wildlife and nature photography. If it was just that, I think I would be happy with Canon 300mm f/4L IS. But I still like to do bird images. And I still feel I need to go longer than 400mm. (I should point out that I am using crop cameras - 30D and Rebel XT.) So I am thinking that the 300 f/2.8L IS might be the better choice - without TC for the stuff mentioned above and with a 2x TC for birds. That would give me 600mm at f/5.6 and I should be able to keep autofocus.

Does that make sense? Is the f/2.8 too bulky for flowers, butterflies and such? Any other advice?

Thanks.

I know a number of people who use the 300 2.8 IS for both birds and macro. You already get good close focus with the 300, but extension tubes will really help when shooting macro. The 300 2.8 is very sharp, but sharpness does suffer with the 2x. According to a recent NatureScapes article, the 400 5.6 is sharper than the 300 2.8 + 1.4x combo, but of course you've already got the 400 5.6. I think the 300 2.8 is a good hand held flight lens, and is good for 600mm when you really need the reach. My girlfriend just got the 300 2.8 for many of the same reasons that you mentioned, and she loves it.

Hi Ed For the price of the 300 2.8 you are getting close to a 500 f4.0? Would make more sense to save?

I use a 300 2.8 and is incredibly sharp. I'm not familiar with the article comparing the two lenses but I'm sure they are so close you cold not tell the difference in the real world (only my personal opinion) I think the big difference is in slowing down the AF. btw I have used the 400 5.6 with a 1.4X and it is very acceptable !!!! With the pro body cameras the AF works.

Thanks Doug. Thanks Al. Appreciate your thoughts here.

Al if I was looking for a lens just for birds, I would agree that the 500 would be the way to go. But because I am looking for a lens for multiple outdoor/nature subjects from wildflowers to butterflies to birds to wildlife, I keep thinking the 300 would be a better choice particularly if it can produce very good quality images with a 2x TC.