100-400mm Or 400mm Prime?

I borrowed both 100-400 and 400/5.6L at the same time. I found the 400/5.6L to be a little sharper and well balanced and light enough that I could hand hold it on my 5D3 for awhile. Also worked great on a monopod. It's minimum focus distance is a pain and it is a bit longer. In short I honestly don't miss the IS with the 400/5.6L.

Never was that happy hand holding the 100-400's.

If you plan on shooting mostly on the 400mm end --- or longer with 1.4x tele-converter, I'd go 400/5.6L.

The 100-400L covers an awesome focal range. Great when shooting kids and insects that move close and far. The primes and shorter zooms may require attaching / detaching teleconverts to keep up.

If I had to chose one without any further information, I'd go 100-400.

I have yet to own/try the 100-400, but have used and own the 400 f/5.6.

Due to the weight, its not bad at all to carry around. Perfect zoo lens IMO, except for things up close but that is quite rare anyway. If they are, I generally swap lenses out anyway for something faster such as the 135L or 24-70 II. I went with just my 400 one day though and nothing else and had a blast with it. It is a very fun lens. It is sharp and AF is very snappy.

I am still waiting for an updated 100-400 though... I think I would sell the 400 prime and switch once they do. Newer 4-stop IS, hopefully extreme sharpness on both ends like all the newer zooms they release, etc... But until then, I dig the 400. Takes an extender quite well too on the 5D3! Wide open it still looks good, but stopping down to f/9 makes for an excellent image.

The minimum focus distance hasn't been mentioned yet. It's quite a difference between the two, and may be the difference between getting a superb close up or sitting there watching something unfold as a spectator.
I have the 100-400, I bought a 300 prime to use with TC's. I was shocked how hard it is to keep a 400mm lens steady without IS. Only you know how steady your hand is, or as I do use a monopod which make certain shots tricky to react quickly to..........

The 300 f/4 IS is another very good option. I really like that lens and was debating between that and the 400 when I bought it... With an extender, you have a 420mm f/5.6 with IS and IQ is still very good. But I decided on the 400 because I would prob have the extender on 75% of the time anyway. But the MFD on the 300 is SO nice as stated above.

Thankfully, I don't run into MFD issues too much with the 400... Generally I am shooting things at distances and it is not as bad as I remember it being when I had it before.

Invertalon wrote in post #16048481
I have yet to own/try the 100-400, but have used and own the 400 f/5.6.

Due to the weight, its not bad at all to carry around. Perfect zoo lens IMO, except for things up close but that is quite rare anyway. If they are, I generally swap lenses out anyway for something faster such as the 135L or 24-70 II. I went with just my 400 one day though and nothing else and had a blast with it. It is a very fun lens. It is sharp and AF is very snappy.

I am still waiting for an updated 100-400 though... I think I would sell the 400 prime and switch once they do. Newer 4-stop IS, hopefully extreme sharpness on both ends like all the newer zooms they release, etc... But until then, I dig the 400. Takes an extender quite well too on the 5D3! Wide open it still looks good, but stopping down to f/9 makes for an excellent image.

In my case, the 400mm prime would be way too restrictive at our zoo. We have a membership, so zoo visits are frequent for us. I use my 100-400L throughout its focal range on each visit. Quite often this will be the only lens I bring when I do not want to carry a camera bag, and the only thing it doesn't do well are a few of the indoor exhibits (specifically the reptile and penguin exhibits), but using the 5D3's high ISO capabilities I can even work around that in some cases. Since getting a cheap deal on a refurbished 40mm pancake, I will also stick that in my pocket just in case I need something wider, but that is rare.

Yeah it really depends on the zoo for sure... Ours is quite spread out and wide open, exhibit wise. But some zoos I have been are more "intimate" and would require much less focal length as you said.

Invertalon wrote in post #16048531
Yeah it really depends on the zoo for sure... Ours is quite spread out and wide open, exhibit wise. But some zoos I have been are more "intimate" and would require much less focal length as you said.

Yes, it definitely depends on the zoo. Some of the exhibits at ours are spread out like you described, while others allow you to get quite close to the animals.

Here is a grizzly bear from our last visit, at 180mm, as an example: