Canon 400mm f/5.6 for Birding???

I'm thinking of getting this lens for my Canon 5D (full frame) to use for birding and wildlife. Currently my longest lens is the 300 f/4.0 IS which was nice when I had a crop camera, but just isn't long enough with a full frame camera. This lens has no IS and isn't a fast lens, but I can't afford any of the other 400mm lenses. I'm wondering if any of you use this lens for birding and would either recommend it or not. Thanks in advance.

I would likely switch or add a new camera to my collection rather than buy a 400 5.6 for your purpose. If you get a crop body like a 7d, 50d, or 40d, you will increase the effective focal length of your lens (1.6 x 300= 480mm). You will save money if you buy a 50d or 40d, and you could break even if you buy a 7d used. If you switch to a 400 5.6, you lose a stop of light and image stabilization, both of which are extremely significant in getting the shot you want. I do not believe there are any advantages in terms of image quality between the 400 5.6 and the 300 f4. I've only used the 300 though.

I would just buy myself a Canon 1.4x extender, about the same difference..
Know a few people who use that combo with excellent results.
A whole lot cheaper too

Thanks for your responses so far. I already own a 1.4TC which I use on the 300mm and would also use on the 400mm (without autofocus). I had seriously given thought to buying a 7D instead of a new lens, but since I work too much and don't get out to shoot nearly enough I doubt my ability to master two very different camera bodies. I'm going to have to give that some more thought though.

I had a 100-400mm and sold it to buy the 400mm F5.6 for bird photography. I've never regretted the decision! The 400mm f5.6 seems to let in a bit more light, and is quick and accurate with it's focusing. Great for birds in flight.

I have some friends who use the 400 F5.6 and they love it. It's excellent for flight photography, lightweight and the af is pretty fast. It doesn't have the IS but for flight photography you are usually using pretty fast shutter speeds so you don't need it anyway. If you are using it in lower light a tripod should give you the stability you need. I think it would be a fine choice to use with that camera body.

You can simulate the effect of a crop camera, simply by cropping the images your camera produces. My money would go for the lens.

I can't speak from personal experience, but Canon's 400mm f5.6 lens has a good reputation as a flight lens. I used one once, briefly, and was impressed by it's small size and light weight. (Considerably smaller than 70-200 f2.8, for example) Wouldn't it be great if they made an IS version?

I would definitely get the 400/5.6. It is a really, really sharp lens, and for birds in flight and most wildlife, you need a fast shutter speed so IS isn't important. It is relatively lightweight, and focuses fast. I replaced my 100-400 with the 400 and have never regretted it. If I'm going to be sitting somewhere for a long time, I put it on my tripod, attached to the Wimberley sidekick.

Rather than put it on a full frame body, you could trade your 300 lens for a used 40D. I don't recommend the 50D; mine had a lot of noise. The 5D frame rate is too slow for wildlife shots, especially BIF, in my opinion.

I currently have the 7D and the 5D mkII. It is no big deal to use two different bodies, and I love having the flexibility of having a setup for wildlife and one for landscapes, etc. I carry both rigs, fully assembled without backpack, when I do half-day hikes and I'm a small person. The menus are similar enough that I have no trouble switching back and forth.

I use the 400 mm f/5.6 attached to my 7D regularly in hikes, sometimes with a monopod, but most often just handheld. I tried the 100-400 mm f/5.6 and the 1.4 EX on the 400 mm f/5.6. However, although the former system gave plenty of flexibility I found it often did not seem as sharp as the 400 mm. The 400 mm has a nicer looking MTF curve that provides support for that result. The loss of autofocus when using the 1.4 EX on the 400 mm was something I struggled with for some time. I loved the extra reach but missed so many shots either because the bird got tired of waiting for me to manually focus or because my focus just was not good enough. For manual focus I eventually used live view and affixed a hoodman to the rear of the camera with elastic bands. That helped my focusing ability but still took too much time. Currently I’m experimenting with cropping my images more than most photographers do. Often the details hold up quite well, especially with good light, mainly because of the sharpness of the 400 mm lens I think.

That 400/5.6 is the unknown gem of the Canon lens lineup. I had a 400mm/5.6 for a while, and now wish I didn't sell it. I uisede it on my 5D MKII (I used to have a 5D) and to me that razor of a lens works superbly on the full frame body for two reasons: 1, the full frame viewfinder is bigger making the darker 5.6 lens easier to see through and 2., you can crank up the ISO on our FF sensors beyond crop cameras, gaining back some shutter speed, AND/OR crop in on the shot without losing all detail. Add a monopod and your set if you want to remain mobile, the 400/5.6 is light enough for that. On a tripod, sharpness will be adundant! Our 5Ds have one drawback for birding though, the FPS. 4 frames a second max is so-so for birding or sports, but it is what it is. Get yourself the 400, you won't regret it, and if you do, the resale value is huge!

I have the 300/4L IS as well and love it to bits. But I do more than just birds. I did use the 400/5.6L extensively earlier this year and I can say that in GOOD light it is an AWESOME and VERY FAST lens. Much faster at acquiring AF (I think) than the 300/1.4x combo. I used the 400 and a 1.4x with taped pins with some success and in good light I could get slow AF. Here is a picture with that combo. It's about 80% of FF. I was relatively happy.

http://amatteroflight.com/gallery2/d/1419-1/Grey-Fantail_6003.jpg

But without converters the 400 is a killer lens in good light. One that I will DEFINITELY add to my arsenal someday.