Birders: anyone use BOTH the 400L and 100-400L?

I've been toying with the idea of getting a new (better) lens in addition to my 100-400L. I really want a 500 f4 but even a used MK1 is out of my price range. I then thought about the various 300 f2.8 options (including the new Sigma zoom) but I have my doubts about these, obviously for birding I'd be using teleconverters and I'm wondering if they'd be worth it what with the extra weight and cost.

So I've been thinking about the 400 f5.6 prime. It's not expensive and seems to get universally good write ups. Do any of you own and use both these lenses regularly? Do they complement each other? I was kind of thinking the 400 would be my BIF/sunny weather lens and the zoom my poor light/walkabout lens. Is it worth having both? Any experiences would be gratefully received.

If you have the 100-400, I would just stick with that and use it. But to have both may be a bit redundant.

From what I've read, the 100-400 keeps most of its sharpness right out to 400. This is not true of many zooms, of course. So to me there doesn't seem much advantage to getting the 400. I have a 400 and bought it instead of the 100-400, but if I already had a 100-400, I wouldn't get a 400, since they do seem pretty redundant to me.

If you are hankering for a new lens, maybe something different like a macro lens? I don't know what you have, but I certainly understand wanting to get a new lens!

Invertalon wrote in post #13497339
If you have the 100-400, I would just stick with that and use it. But to have both may be a bit redundant.

I hear you and yes I'm worried about that, just interested to hear about those who own and use both.

RAH1861 wrote in post #13497384
If you are hankering for a new lens, maybe something different like a macro lens?

My wife already has the 100 f2.8L (and there's a a Tamron 90mm macro in a drawer somewhere too)...........

I had both for more than 1 yr. Started with 100-400L and then picked the prime based on user reviews. In the end, my copy of 100-400L was real good and very minor differences in final image quality. But with 100-400L I had to shoot at f7.1 while prime was super sharp at f5.6.

For BIFs, prime all the way. Even for other situations I found you can easily shoot prime at lower ss as long as you use some support like tripod or even monopod.

bobbyz wrote in post #13497454
I had both for more than 1 yr. Started with 100-400L and then picked the prime based on user reviews. In the end, my copy of 100-400L was real good and very minor differences in final image quality. But with 100-400L I had to shoot at f7.1 while prime was super sharp at f5.6.

For BIFs, prime all the way. Even for other situations I found you can easily shoot prime at lower ss as long as you use some support like tripod or even monopod.

Thanks for the reply Bobby. So you kept the prime?

Sold both and moved to 500mm f4 IS. Much much better.

I had both at the same time and kept the 100-400. Unlike Bobbyz's copy, mine is sharp at f/5.6.

To be fair, sharpness is subjective... One man's sharp is another man's soft copy

I did not actually own both but I tested 4 copies (2 of each) when I was in the market.

We tend to use 'sharp' as the goto differentiator but in this case I noticed zero difference at 5.6
...so other factors need to be considered (IS - size - weight - weatherproofing - versatility - filter 'situation')

Ultimately I went with the 100-400 but I admit it's not a designated birding lens for me.

Unless you are mad about BIF, I'm not sure of the merits of owning both of those lenses.

I've got the 100-400L and it's a beauty. I often shoot at f7.1, but it's sharp at f5.6 (subjective as stated above - but I'm a stickler for sharp photos!)

I'm currently looking at the Sigma 120-300 f2.8 OS & 2x TC combo as my next lens, from some of the examples I've seen with this combo, especially at 600mm, I think I'd be satisfied with the IQ. Seems like a pretty good way to get that extra reach without the costs associated with the Canon big primes.

Thanks for the comments, you're confirming what I expected: I think in my situation maybe it's overkill to have both lenses.............

I'll think about the 300 f2.8 options maybe (a secondhand Canon 300L IS MK1 or the new Sigma 120-300 OS are in my price range, just).

I owned both for over a year as well. The 400/5.6 had a very slight edge but not enough for me to want to hang on to both and since the 100-400 was quite a bit more versatile I sold the 400/5.6.