Want a 400mm & have 2 options....

they are both already really slow lenses... at 5.6 the 400 prime is sharp, with little improvement stopped down.

The 100-400 is not at the same weight, i travel a lot and shoot at 400mm and also travel with a 70-200 2.8 so a 100-400 is just useless for me.

If you want a light 400, the prime is a great choice, if you want a versatile 400 and dont mund extra weight the 100-400 is a better choice.

Think about if you need the range between 100 and 400. If not, then just get the 400mm. It's a no brainer for me since the 100-400 just isn't on the image quality level as the 400mm. Use a monopod and don't worry about IS too much.

The 100-400 at 400/5.6 is almost indistinguishable in the centre frame form the prime for sharpness.

I'd rather have a lens that was sharp all around than one that is sharp just in the center. For the OP, here's a reference:
http://www.the-digital-picture.com …omp=0&FLIComp=7​&APIComp=0

I have the prime 400mm and love it, particularly in good light condition for contrast. I use it just for birding. This lens on 7D lets me crop a lot. Unfortunately the min focusing distance is 3.5m

Here is an excellent comparison between the two lenses. Please read...

http://www.luminous-landscape.com …enses/forgotten​-400.shtml

I owned the 100-400L BEFORE I bought my Sigma 70-200 OS. The 100-400L gets used a lot less, now. And mainly at or near 400mm. I wish I had the prime instead. Oh, and the IS is almost insignificant (for me) at 400mm. At the 1/800 and faster shutter speed that 400mm requires on a 60D, the IS is just about pointless.

I found my 100-400 hit and miss, it was inconsistent. Sharpest for me at f7.1 and slightly soft wide open. Got rid of it after a month.

Snydremark wrote in post #15384261
The only way I feel this is even fully true, though, is if you are only shooting birds in flight; otherwise, stationary birds frequently hang out in shady/covered spots where having the IS on the 100-400 comes in pretty handy since you may not be able to keep your SS up, appropriately, for the prime.

Why particularly with higher ISO these days. If bird is perched you don't need say more than 1/500, 1/650 and that shouldn't be any problem at f5.6, ISO400. For perched birds, better to have smaller tripod. I knew someone who would use bogen monopod with three little legs for her rebel and 400mm f5.6 and her pictures were better than 99% of us folks.

nightcat wrote in post #15384651
Here is an excellent comparison between the two lenses. Please read...

http://www.luminous-landscape.com …enses/forgotten​-400.shtml

That is the worst lens comparison and needs to be done again. Honestly. 100-400L is much much better than LL sample suggest.

I do a lot of bird photography and the 100-400 is much better for me. Many times the subjects come in close, if I only had the 400mm lens I would miss the shots. I have found 7.1 is the sweet spot on my lens.

I have the 400 prime, but then again I pair it up with my 70-300L when I use it, primarily at racetracks. Sure, this is going to require me to change lenses, but since I use my 70-300L for other things as well (zoo, family stuff) it's a price I'm willing to pay. Not to mention the total weight of those two lenses in my lightweight hiking backpack feel like nothing to carry around.

Also- consider if you want to use a 1.4TC on your 400mm lens. I tried a non-reporting kenko 1.4TC on my old 100-400L, and it didn't work well at all, or give too good of results with my 7D. The 400 prime on the other hand takes the TC much better than it was designed to with my 7D, and the AF and IQ are both manageable as long as you're outdoors.

Just some things to consider beyond simply the IQ between the two, as both are very capable lenses.

I'm waiting on a new 400mm to release, the rumors keep saying 2013!! D:

But if I were to choose now I'd get the 400mm f/5.6L.

I just did a search for threads comparing these two lenses, and came across this one. Good timing.

Already having the 70-200 f/4L, and a 1.4XTC, it seems the 400 prime would make more sense for me (and I really like IS lenses for my unsteady hands). If I didn't have those two things (70-200 and TC), I'd probably opt for the 100-400.

Is this reasonable thinking?

Vixen89 wrote in post #15385327
I'm waiting on a new 400mm to release, the rumors keep saying 2013!! D:

But if I were to choose now I'd get the 400mm f/5.6L.

I am also curious about the new 400mm lenses. One is said to be a 400mm f4 with IS. Thankfully, this will NOT be another DO model, so the IQ should be top of the line. I wonder about pricing. I'm hoping $3000.00 or less. Maybe that's wishful thinking.