Tannin
08-06-2017, 1:04pm
Having retired, I am doing a full review of my gear, with a view to getting lots of photography in now that I'm no longer tied to the office. (Not that work responsibilities ever stopped me in the past, alas!) Today's topic is the birding lenses.
I've given a lot of thought to this over the past few months, and every big lens on the market has good reasons in its favour, as well as good reasons against. Canon alone make no less than 8 different lenses 400mm or above (Nikon make 9) and every single one is unquestionably "the best lens" for some particular purpose. That's why they make so many different ones. Plus there are the third-party lenses, not to mention the two recently discontinued Canon models I already own.
For weeks - well, years really - I've been finding reasons to buy a 600/4, or a 400/2.8, or upgrade my 500/4 "1" to a "2", and so on. And because there are so many different situations you use a birding lens in, it's very difficult to decide if one needs the reach of a 600/4 more than the low-light capacity of a 400/2.8, or the portability of a 400/4 DO. And I certainly can't afford to buy one of everything! I get very confused.
So today I made a list of the things I actually do with a birding lens, and then for each of those things, rated the candidates on a scale out of 10, with "10" being "the best possible lens for this job in 2017", and "1" being "the candidate lens least suited to this task". For example, an 800/5.6 might score a 10 for working waterbirds from a hide, but only 1 for rainforest work.
Working from a car. I do this a lot.
Short walks where you handhold and don't wander too far from the car or campsite.
Short walks using a tripod.
Long walks, handheld. By "long" I mean anything that takes more than an hour or so.
Long walks with tripod. As above.
Rainforest, or any other dark environment.
Close-up. For small birds where minimum focus distance becomes an issue.
Landscape. Some long lenses are also good for landscapes.
THE CANDIDATES.
These are all the lenses I am seriously considering, plus the two I already own. Not considered are the 800/5.6 (heavy, expensive, and too slow), the third-party lenses (no current model seems to present itself as a candidate), and anything shorter than 400mm other than a 300/2.8 (which becomes a 420/4 or a 600/5.6 with converters) and the 70-300 I rather fancy for my landscapes. Prices are educated guesswork. My current camera bodies are a 1D IV and a 7D II. There is probably also a 5D IV in my future somewhere.
600/4L IS II: 3.9kg, $14,000
500/4L IS II: 3.2kg, $11,500
500/4L IS: 3.9kg, $5000 (What I could sell it for.) (Guess!)
400/2.8L IS II: 3.8kg, $12,500
400/4L IS DO II: 2.1kg, $9300
200-400/4L IS: 3.6kg, $13,000
300/2.8L IS II: 2.3kg, $8000
100-400/4.5-5.6L IS II: 1.6kg, $2700
100-400/4.5-5.6L IS: 1.4kg, $900 (Same as 500/4.)
70-300/4-5.6L IS: 1kg, $1400
Apart from the unique 400/4 DO, all of the lenses listed have direct Nikkor equivalents, which is why this is in general gear talk instead of the canon-specific forum. (Nikon shooters face the same issues.) There are also two or three third-party models in this class. Most of the long third-party lenses are smallish f/6.3 zooms which I haven't considered here.
IN-CAR USE
I work from inside a car a lot. It's by far the best way to do open country birds like bushlarks and songlarks, and also good for raptors, robins, all sorts of creatures. In the car, it's all about reach. And then more reach.
10: - (no lens seems perfect for this)
9: 600/4 II
8: 500/4 II
7: 500/4
6: 400/2.8 II; 400 DO II; 200-400
4: 300/2.8 II
2: both 100-400s
1: 70-300
In any normal-sized car, length is the key issue; weight not so much. At a physical length of around 550mm (or 575mm with a 1.4 converter), both 500/4s are awkward but manageable; the 630mm 600/4 would be a real handful (which is why it gets only 9 out of a possible 10); the 400/2.8 and the 200-400 at around 500mm with hood would be fine but a little lacking in reach; all the others are much smaller and very easy to manage.
For this use case, one cannot justify spending $9000 to changeover to a new 600, or $6500 for a 500/4 II. The extra reach of the 600 would be more than handy, but the extra length would be a right PITA. The only other lens of real interest here is the 400/2.8, and its potential value all depends on how well it performs with a 2.0x converter. The fairly small image quality loss can be accepted: they key issue would be auto-focus speed with the 2x. (Ditto the 300/2.8.)
Conclusion: keeping the 500/4 is a no-brainer for me. (Those without an existing big lens should look at a 500/4 II or 600/4 II for this use case.)
TRIPOD (semi-static)
By "semi-static" I mean anything where you don't have to carry the gear more than a few hundred metres at a time. I often work just a short distance from the car or camp site. This use depends a bit on your vehicle and how willing you are to use rough tracks. If you stay close to bitumen and organised campsites, you usually need to walk further. I prefer to find a really nice spot in secluded bush and let the birds come to me. Wetland hides are another example of semi-static use - but depending on the length of the access track: some are more like route marches! Weight doesn't matter for semi-static use, only reach.
10: 600/4 II
8: 500/4 II; 500/4
7: 400/2.8 II
6: 200-400;
5: 400 DO II; 300/2.8 II
2: both 100-400s (too short)
1: 70-300 (way too short)
Again, the 600 is king, followed by the two 500s, and again the proper place for the 400/2.8 depends on AF with teleconverters. (Published stats don't tell you this!) The other f/4 400s are a bit short, the 300/2.8 would need a 2x converter, and the smaller zooms are uncompetitive.
Conclusion: for me, keep the 500/4. (For those without an existing big lens, the 600/4 is clearly the best again.)
HANDHELD (semi-static)
Now we are looking at shooting hand-held, still carrying the gear only short to moderate distances. The key here is your ability to hand-hold the lens, and that varies greatly between individuals. If in your day job you play front row for Manly, you can hand-hold even a 5.4kg 600/4 Mark 1 all day long. If you are built more like a jockey, anything bigger than a 2.1kg 400 DO or a 2.4kg 300/2.8 will stretch you. I've always found hand-holding the 3.9kg 500/4 difficult but doable. It's a pain, yes, but the pain is worth it. Alas, I'm not getting any younger and I'm not too keen on too much more of it!
10: 500/4 II (3.2kg)
9: 400 DO II (2.1kg)
8: 200-400 (3.6kg); 600/4 II (3.9kg)
7: 500/4 (3.9kg);
6: 400/2.8 II (3.9kg); 300/2.8 II (2.4kg)
5: 100-400 II (1.6kg)
4: 100-400 (1.4kg)
2: 70-300 (1kg)
This is a really difficult use case to assess. The eternal conflict between weight, reach and speed leads to even more contradictions here than usual. Think it through: you are standing in a patch of bush and the birds are active all around. What lens would you most like to be holding? Despite its still significant weight, the reach and speed of the new 500/4 II makes it the most attractive compromise of all - but only if you are built like me: medium size, medium fit; big front rowers might go for a 600/4 II (which weighs no more than the old 500/4 after all) and jockey types for a 400/4 DO. The DO, despite being a bit light-on for reach, is fast and almost as easy to hand-hold as the little zooms. And although it's rather heavy for a 400 f/4, the 200-400's ability to zoom and more-convenient-than-any-other built-in 1.4 converter makes it another serious candidate.
The 300/2.8 is small and reasonably light. The reality is that you'd always have at least a 1.4 converter on it (420mm f/4) and probably a 2x converter (600mm f/5.6) most of the time. The loss of image quality isn't too much of a worry, but for hand-held birding, focus speed is critical and I've downgraded it accordingly. The very heavy 400/2.8 strikes me as inferior to the equally heavy 500/4 (mark 1) and 600/4: it is always going to be one step further up the teleconverter ladder for similar reach (a 1.4 where they are bare lens; a 2x where they have a 1.4) and even the very best of lenses always lose responsiveness with converters mounted.
There is also something to be said for the three small zooms: they lack reach and light-collecting ability but are so light that hand-holding is effortless. With a small, light lens you move much more quietly, and your body language is different: smoother, more relaxed. Birds are very keyed in to body language and you can get comfortably closer to them with a 100-400 than you can with a 500/4. In camp I often pick up the 100-400 instead of the 500/4 for that reason, and also because you can move through and shoot through obstacles you wouldn't tackle with a big lens. And you can stand holding it to your eye for ages, which you can't with something weighing more than twice as much. But I usually put it down again and go back for the big iron as soon as I get frustrated by the narrower aperture, or the lack of reach, or the slower focus speed. That usually takes about five minutes.
(Outside the Canon universe, there is the 2.3kg Nikkor 200-500/5.6 which sounds interesting, a near-twin of the 100-400, and a host of small third-party 500 and 600mm zooms - all f/6.3 at the long end which rather spoils them, I always think.
Conclusion: 500/4 II followed by 400 DO for me. Your choice will depend on your build. This is probably the use case where our individual answers will differ the most.
HANDHELD (long walk)
Now let's suppose we are going to walk a good distance, keeping an eye out for birds along the way. Weight becomes critical, but we still want reach.
10: 400 DO II (2.1kg)
8: 300/2.8 II (2.4kg)
5: 100-400 II (1.6kg); 100-400 (1.4kg)
4: 70-300 (1kg)
2: 500/4 II (3.2kg);
1: 600/4 II(3.9kg); 500/4 (3.9kg); 400/2.8 II (3.9kg); 200-400 (3.6kg)
The 400 DO stands alone for this task. Only the shorter and slightly heavier 300/2.8 challenges it, and once again we are in the murky waters of 2x converters if we want some decent reach. Next best choices, and even lighter, are the two little 100-400 zooms, followed by the 70-300. Last, all the big iron. I've walked 5 and 10 kilometres carrying the 500/4, but it isn't fun, and all of the big iron is in much the same broad weight class. I should also mention the various third-party zooms in the 150-600 class. I'm not considering them for myself (though I'll certainly read testimonials from owners with interest) but I imagine that they would slot in between the 300/2.8 and the shorter but lighter and faster Canon zooms - in other words, they would be pretty good choices for this use case.
Conclusion: 400 DO II.
TRIPOD (long walk)
Let's try the walk again, but carrying a tripod this time. It's not quite the same question. If we are going to carry a proper tripod and head, there is around 2kg already. The camera body adds between 0.9kg (semi-pro models) and 1.4kg (pro models) so even with the little 70-300 we've already got more than 4kg on the shoulder. No matter what we do there is going to be some pain before the day is out. It seems to me that we need to see something valuable in return for that effort, and this rules out the small zooms. Equally, I've walked 10k in a day a few times with a 1D III and the 500/4 Mark 1 over my shoulder, and never been more pleased to put the damn thing down at the end of it. Don't want to do that again.
10: 400 DO II (5.1kg total)
8: 300/2.8 II (5.4kg total)
6: 500/4 II (6.2kg total);
3: 600/4 II (6.9kg total)
2: 500/4; 400/2.8 II; 200-400 (6.9, 6.9, and 6.6kg total respectively)
1: 100-400 II; 100-400l 70-300 (4.6, 4.4, and 5kg total respectively)
I've scored the 400 DO and the 300/2.8 high because they provide the most reach for the least weight (unless we want to consider the third-party f/6.3 zooms, which mightn't be a bad idea for this job), and the 500/4 II next as it's the only one to provide 500/4 and 700/5.6 reach short of grossly unreasonable weights. I've discounted the small zooms - I'm not going to carry 3kg of tripod and body all that way for a camera anyone under 90 years old can hand-hold without much trouble.
(Consideration of tripod, head and camera body weight might be fruitful here - a mirrorless EOS M is around 300g, and there must be decent heads that weigh less than a full Wimberley - but that's probably best left to another thread.)
Conclusion: 400 DO II again.
RAINFOREST (and similarly dark habitats)
Reach is much less important. Light is critical: it's pretty much f/2.8 or bust. (Curiously, I can't remember exactly why f/2.8 is so important in rainforest. It's been a few years since I last spent any time in one and the main thing I remember - not just once but many times - is a constant yearning for something - anything! - faster than f/4. In desperation, I once even tried using a 100mm f/2.8 macro for Bassian Thrushes because it was the longest fast lens I had.)
10: 400/2.8 II
8: 300/2.8 II
5: 600/4 II; 500/4 II; 500/4; 400 DO II; 200-400
1: all three small zooms
In rainforest, 300mm would do at a pinch. You can't really hand-hold if you are using more than a tiny bit of fill-flash (because getting the flash far enough off-camera is impractical) so size and weight mostly only matter from the point of view of making your way down narrow, obstructed paths. Given the necessity of a tripod and flash bracket, light weight is only of minor benefit.
On the other hand, if you are at 300mm f/2.8 with (say) a 7D II, for the same framing you can go to 400/2.8 on an FX or APS-H body and effectively gain another stop. Let's put that another way in case it isn't clear. In half-decent light, you can get away with a not-quite-long-enough lens by using a pixel-dense camera body on it. If you have (say) a 5D II and a 60D, the smaller-format camera will put more pixels on the bird and effectively give you more focal length. But the price you pay for those free "extra millimetres" is sensor noise. At ISO 400 you can afford it. If you are already at 1600 ISO, you can't.
This makes the 400/2.8 a clear best choice for rainforest, followed by the 300/2.8, leaving all the f/4 lenses well behind, and the f/5.6 zooms nowhere. (I've used a 100-400 in rainforest and even got a few good shots with it. But it's really not a suitable tool for the task.)
Conclusion: Clearly the 400/2.8 II, or at least the 300/2.8 II. Nothing else comes close.
SMALL BIRDS
The Achilles heel of big telephoto lenses is minimum focus distance. One of the very best things about the old 100-400 is that it focuses down to 1.8 metres. At 1m MFD, the new 100-400 is even better, as is the 70-300 at 1.2m. Of the bigger lenses, both the 200-400 and the 300/2.8 II focus to 2m, which is excellent.
10: 200-400 (2m)
8: 400/2.8 II (2.8m); 300/2.8 II (2m); 100-400 II (1m);
7: 100-400 (1.8m)
5: 70-300 (1.2m)
4: 500/4 II (3.2m); 400 DO (3.3m)
2: 600/4 II (4.5m);
1: 500/4 (4.5m);
In practice, the great divide for this task is whether you need a close-up ring or not. If you are settling down for a good session at a watering hole on a hot day, fitting a close-up ring is no hardship. On the other hand, there are few things more frustrating than spending hours trying to get within 10 metres of a special bird only to have it flip up onto a branch 3 metres away to have a good look at you out of each eye in turn while you stand there holding a lens that won't focus closer than 4.5 metres knowing perfectly well you haven't got a snowball's hope of changing lenses or putting a ring on before it flips off into the shrubbery again.
Conclusion: the 200-400 wins by a mile. This is probably the perfect small bird lens. Also noteworthy are the two f/2.8 lenses, both of which go quite close and focus very fast indeed; and the three small zooms (which score lower in my book despite their excellent MFDs because they are slower, and small birds move fast).
LANDSCAPES
Medium-long lenses are fantastic for landscapes. Every proper lens manufacturer of the planet makes at least one 70-200. Canon make four different ones and Nikon three. Curiously enough, I have never owned one. Instead, I use the long end of my 24-105 and the short end of the old 100-400. In this role, I'd prefer a 70-300, but the old faithful 100-400 does the job.
10: 70-300
9: 100-400 II
8: 100-400
4: 200-400
2: 300/2.8 II
1: 400 DO; 400/2.8 II; 500/4 II; 500/4; 600/4 II
Captain obvious can see the answer to this one.
Conclusion: any of the small zooms, or a 70-200 if you have one.
TOTALS
Having looked at these various use cases, which lenses do the best overall? (Bearing in mind these tasks are the ones I use long lenses for (your use may be completely different); that the rankings reflect my likes and dislikes (yours may well be different); and that I have used only a few examples - while I can confidently guess what a 600/4 or even a 200-400 is like, I'm on much shakier ground with exotica like the 400 DO and also the 2.8s with big converters.)
Let's just add up the scores and see if that tells us anything. No - on second thoughts, while each of these use cases is important to me, they are not all equally important. Let's cross out the landscape category. Realistically, I'm always going to have a lens that does this: if not the 100-400, then a 70-200 or 70-300.
Also, there are four different categories for walking around and only one each for rainforest and in-car. That's going to bias results, so let's weight them.
What do I do most of? Least of? Off the top of my head, working from a car: 25%. Long walks, handheld: 5%. Long walks with tripod: 10%. Short walks, hand-held: 20%. Short walks with tripod: 20%. Rainforest: less than 10%, but it's something I particularly want to master, so call it 20%. Close-up: I do this quite a lot, but I can always just use rings. Let's ignore it.
By a miracle, these rough-guess proportions total led to exactly 100% first go! Let's use them.
We simply multiply the scores by the weighting percentage. (Expressing it as a whole number to save having decimals.) This produces scores for each lens out of a possible maximum of 1000. (Note that a 1000-lens wouldn't be the perfect birding lens, it would be my perfect birding lens - which is precisely the point, of course. If you want your perfect lens, do your own numbers. Only takes a few hours if you know how to use a spreadsheet. You've stood under a tree waiting for a bird to turn up for longer at a time than that.)
730: 500/4 II
720: 600/4 II
680: 400/4 DO II.
615: 400/2.8 II
600: 500/4
620: 300/2.8 II
555: 200-400/4
245: 100-400 II
225: 100-400
130: 70-300
Clearly, I should race out and order a 500/4 II. Yes?
Well, no. I already have an older 500/4 which is very nearly as good as a 500/4 II in all respects bar weight. A 500/4 II would be a major convenience, not really a game changer. Then there is the 600/4: it would certainly be a handy upgrade - but not a revolution. It too is best at the things the old 500 already does very well indeed. Who wants to spend $14,000 for a mere "handy upgrade"? Well, maybe $9000 if we consider the changeover cost. Just the same, I still dream about the weight of a 500/4 II.
Now we get to the interesting one: the 400/4 DO II. Set rainforest aside and it's the best or close to the best at everything the 500/4 is not so good at; and the things it is weakest at, the already-paid-for 500/4 does well. They're a matching pair. (It would match even better with a 600/4. If you wanted two lenses with cost no object, those two would be very hard to beat.)
But why not buy a 300/2.8? In many ways it's a sort of a poor man's 400/4 DO after all: a bit short, reasonably small and light, something you could carry all day. And it's the second-best rainforest lens. This looks very much like the most sensible thing I can do: keep the 500/4 and the 100-400, simply add a 300/2.8.
But then i think about lyrebirds and Logrunners and pittas and Bassian Thrushes and Pale Yellow Robins and I'd really like a 400/2.8 .....
Hours of work and 3000 words on, I'm still uncertain. Nevertheless, the exercise has been worth it: setting out the strengths and weaknesses of the candidates like this has given me a much clearer grasp of the key issues to be decided. I hope that some of what I've written will be of some use to you too, if you are thinking about big lenses, and I'd be delighted to read of your experiences and thoughts.
I've given a lot of thought to this over the past few months, and every big lens on the market has good reasons in its favour, as well as good reasons against. Canon alone make no less than 8 different lenses 400mm or above (Nikon make 9) and every single one is unquestionably "the best lens" for some particular purpose. That's why they make so many different ones. Plus there are the third-party lenses, not to mention the two recently discontinued Canon models I already own.
For weeks - well, years really - I've been finding reasons to buy a 600/4, or a 400/2.8, or upgrade my 500/4 "1" to a "2", and so on. And because there are so many different situations you use a birding lens in, it's very difficult to decide if one needs the reach of a 600/4 more than the low-light capacity of a 400/2.8, or the portability of a 400/4 DO. And I certainly can't afford to buy one of everything! I get very confused.
So today I made a list of the things I actually do with a birding lens, and then for each of those things, rated the candidates on a scale out of 10, with "10" being "the best possible lens for this job in 2017", and "1" being "the candidate lens least suited to this task". For example, an 800/5.6 might score a 10 for working waterbirds from a hide, but only 1 for rainforest work.
Working from a car. I do this a lot.
Short walks where you handhold and don't wander too far from the car or campsite.
Short walks using a tripod.
Long walks, handheld. By "long" I mean anything that takes more than an hour or so.
Long walks with tripod. As above.
Rainforest, or any other dark environment.
Close-up. For small birds where minimum focus distance becomes an issue.
Landscape. Some long lenses are also good for landscapes.
THE CANDIDATES.
These are all the lenses I am seriously considering, plus the two I already own. Not considered are the 800/5.6 (heavy, expensive, and too slow), the third-party lenses (no current model seems to present itself as a candidate), and anything shorter than 400mm other than a 300/2.8 (which becomes a 420/4 or a 600/5.6 with converters) and the 70-300 I rather fancy for my landscapes. Prices are educated guesswork. My current camera bodies are a 1D IV and a 7D II. There is probably also a 5D IV in my future somewhere.
600/4L IS II: 3.9kg, $14,000
500/4L IS II: 3.2kg, $11,500
500/4L IS: 3.9kg, $5000 (What I could sell it for.) (Guess!)
400/2.8L IS II: 3.8kg, $12,500
400/4L IS DO II: 2.1kg, $9300
200-400/4L IS: 3.6kg, $13,000
300/2.8L IS II: 2.3kg, $8000
100-400/4.5-5.6L IS II: 1.6kg, $2700
100-400/4.5-5.6L IS: 1.4kg, $900 (Same as 500/4.)
70-300/4-5.6L IS: 1kg, $1400
Apart from the unique 400/4 DO, all of the lenses listed have direct Nikkor equivalents, which is why this is in general gear talk instead of the canon-specific forum. (Nikon shooters face the same issues.) There are also two or three third-party models in this class. Most of the long third-party lenses are smallish f/6.3 zooms which I haven't considered here.
IN-CAR USE
I work from inside a car a lot. It's by far the best way to do open country birds like bushlarks and songlarks, and also good for raptors, robins, all sorts of creatures. In the car, it's all about reach. And then more reach.
10: - (no lens seems perfect for this)
9: 600/4 II
8: 500/4 II
7: 500/4
6: 400/2.8 II; 400 DO II; 200-400
4: 300/2.8 II
2: both 100-400s
1: 70-300
In any normal-sized car, length is the key issue; weight not so much. At a physical length of around 550mm (or 575mm with a 1.4 converter), both 500/4s are awkward but manageable; the 630mm 600/4 would be a real handful (which is why it gets only 9 out of a possible 10); the 400/2.8 and the 200-400 at around 500mm with hood would be fine but a little lacking in reach; all the others are much smaller and very easy to manage.
For this use case, one cannot justify spending $9000 to changeover to a new 600, or $6500 for a 500/4 II. The extra reach of the 600 would be more than handy, but the extra length would be a right PITA. The only other lens of real interest here is the 400/2.8, and its potential value all depends on how well it performs with a 2.0x converter. The fairly small image quality loss can be accepted: they key issue would be auto-focus speed with the 2x. (Ditto the 300/2.8.)
Conclusion: keeping the 500/4 is a no-brainer for me. (Those without an existing big lens should look at a 500/4 II or 600/4 II for this use case.)
TRIPOD (semi-static)
By "semi-static" I mean anything where you don't have to carry the gear more than a few hundred metres at a time. I often work just a short distance from the car or camp site. This use depends a bit on your vehicle and how willing you are to use rough tracks. If you stay close to bitumen and organised campsites, you usually need to walk further. I prefer to find a really nice spot in secluded bush and let the birds come to me. Wetland hides are another example of semi-static use - but depending on the length of the access track: some are more like route marches! Weight doesn't matter for semi-static use, only reach.
10: 600/4 II
8: 500/4 II; 500/4
7: 400/2.8 II
6: 200-400;
5: 400 DO II; 300/2.8 II
2: both 100-400s (too short)
1: 70-300 (way too short)
Again, the 600 is king, followed by the two 500s, and again the proper place for the 400/2.8 depends on AF with teleconverters. (Published stats don't tell you this!) The other f/4 400s are a bit short, the 300/2.8 would need a 2x converter, and the smaller zooms are uncompetitive.
Conclusion: for me, keep the 500/4. (For those without an existing big lens, the 600/4 is clearly the best again.)
HANDHELD (semi-static)
Now we are looking at shooting hand-held, still carrying the gear only short to moderate distances. The key here is your ability to hand-hold the lens, and that varies greatly between individuals. If in your day job you play front row for Manly, you can hand-hold even a 5.4kg 600/4 Mark 1 all day long. If you are built more like a jockey, anything bigger than a 2.1kg 400 DO or a 2.4kg 300/2.8 will stretch you. I've always found hand-holding the 3.9kg 500/4 difficult but doable. It's a pain, yes, but the pain is worth it. Alas, I'm not getting any younger and I'm not too keen on too much more of it!
10: 500/4 II (3.2kg)
9: 400 DO II (2.1kg)
8: 200-400 (3.6kg); 600/4 II (3.9kg)
7: 500/4 (3.9kg);
6: 400/2.8 II (3.9kg); 300/2.8 II (2.4kg)
5: 100-400 II (1.6kg)
4: 100-400 (1.4kg)
2: 70-300 (1kg)
This is a really difficult use case to assess. The eternal conflict between weight, reach and speed leads to even more contradictions here than usual. Think it through: you are standing in a patch of bush and the birds are active all around. What lens would you most like to be holding? Despite its still significant weight, the reach and speed of the new 500/4 II makes it the most attractive compromise of all - but only if you are built like me: medium size, medium fit; big front rowers might go for a 600/4 II (which weighs no more than the old 500/4 after all) and jockey types for a 400/4 DO. The DO, despite being a bit light-on for reach, is fast and almost as easy to hand-hold as the little zooms. And although it's rather heavy for a 400 f/4, the 200-400's ability to zoom and more-convenient-than-any-other built-in 1.4 converter makes it another serious candidate.
The 300/2.8 is small and reasonably light. The reality is that you'd always have at least a 1.4 converter on it (420mm f/4) and probably a 2x converter (600mm f/5.6) most of the time. The loss of image quality isn't too much of a worry, but for hand-held birding, focus speed is critical and I've downgraded it accordingly. The very heavy 400/2.8 strikes me as inferior to the equally heavy 500/4 (mark 1) and 600/4: it is always going to be one step further up the teleconverter ladder for similar reach (a 1.4 where they are bare lens; a 2x where they have a 1.4) and even the very best of lenses always lose responsiveness with converters mounted.
There is also something to be said for the three small zooms: they lack reach and light-collecting ability but are so light that hand-holding is effortless. With a small, light lens you move much more quietly, and your body language is different: smoother, more relaxed. Birds are very keyed in to body language and you can get comfortably closer to them with a 100-400 than you can with a 500/4. In camp I often pick up the 100-400 instead of the 500/4 for that reason, and also because you can move through and shoot through obstacles you wouldn't tackle with a big lens. And you can stand holding it to your eye for ages, which you can't with something weighing more than twice as much. But I usually put it down again and go back for the big iron as soon as I get frustrated by the narrower aperture, or the lack of reach, or the slower focus speed. That usually takes about five minutes.
(Outside the Canon universe, there is the 2.3kg Nikkor 200-500/5.6 which sounds interesting, a near-twin of the 100-400, and a host of small third-party 500 and 600mm zooms - all f/6.3 at the long end which rather spoils them, I always think.
Conclusion: 500/4 II followed by 400 DO for me. Your choice will depend on your build. This is probably the use case where our individual answers will differ the most.
HANDHELD (long walk)
Now let's suppose we are going to walk a good distance, keeping an eye out for birds along the way. Weight becomes critical, but we still want reach.
10: 400 DO II (2.1kg)
8: 300/2.8 II (2.4kg)
5: 100-400 II (1.6kg); 100-400 (1.4kg)
4: 70-300 (1kg)
2: 500/4 II (3.2kg);
1: 600/4 II(3.9kg); 500/4 (3.9kg); 400/2.8 II (3.9kg); 200-400 (3.6kg)
The 400 DO stands alone for this task. Only the shorter and slightly heavier 300/2.8 challenges it, and once again we are in the murky waters of 2x converters if we want some decent reach. Next best choices, and even lighter, are the two little 100-400 zooms, followed by the 70-300. Last, all the big iron. I've walked 5 and 10 kilometres carrying the 500/4, but it isn't fun, and all of the big iron is in much the same broad weight class. I should also mention the various third-party zooms in the 150-600 class. I'm not considering them for myself (though I'll certainly read testimonials from owners with interest) but I imagine that they would slot in between the 300/2.8 and the shorter but lighter and faster Canon zooms - in other words, they would be pretty good choices for this use case.
Conclusion: 400 DO II.
TRIPOD (long walk)
Let's try the walk again, but carrying a tripod this time. It's not quite the same question. If we are going to carry a proper tripod and head, there is around 2kg already. The camera body adds between 0.9kg (semi-pro models) and 1.4kg (pro models) so even with the little 70-300 we've already got more than 4kg on the shoulder. No matter what we do there is going to be some pain before the day is out. It seems to me that we need to see something valuable in return for that effort, and this rules out the small zooms. Equally, I've walked 10k in a day a few times with a 1D III and the 500/4 Mark 1 over my shoulder, and never been more pleased to put the damn thing down at the end of it. Don't want to do that again.
10: 400 DO II (5.1kg total)
8: 300/2.8 II (5.4kg total)
6: 500/4 II (6.2kg total);
3: 600/4 II (6.9kg total)
2: 500/4; 400/2.8 II; 200-400 (6.9, 6.9, and 6.6kg total respectively)
1: 100-400 II; 100-400l 70-300 (4.6, 4.4, and 5kg total respectively)
I've scored the 400 DO and the 300/2.8 high because they provide the most reach for the least weight (unless we want to consider the third-party f/6.3 zooms, which mightn't be a bad idea for this job), and the 500/4 II next as it's the only one to provide 500/4 and 700/5.6 reach short of grossly unreasonable weights. I've discounted the small zooms - I'm not going to carry 3kg of tripod and body all that way for a camera anyone under 90 years old can hand-hold without much trouble.
(Consideration of tripod, head and camera body weight might be fruitful here - a mirrorless EOS M is around 300g, and there must be decent heads that weigh less than a full Wimberley - but that's probably best left to another thread.)
Conclusion: 400 DO II again.
RAINFOREST (and similarly dark habitats)
Reach is much less important. Light is critical: it's pretty much f/2.8 or bust. (Curiously, I can't remember exactly why f/2.8 is so important in rainforest. It's been a few years since I last spent any time in one and the main thing I remember - not just once but many times - is a constant yearning for something - anything! - faster than f/4. In desperation, I once even tried using a 100mm f/2.8 macro for Bassian Thrushes because it was the longest fast lens I had.)
10: 400/2.8 II
8: 300/2.8 II
5: 600/4 II; 500/4 II; 500/4; 400 DO II; 200-400
1: all three small zooms
In rainforest, 300mm would do at a pinch. You can't really hand-hold if you are using more than a tiny bit of fill-flash (because getting the flash far enough off-camera is impractical) so size and weight mostly only matter from the point of view of making your way down narrow, obstructed paths. Given the necessity of a tripod and flash bracket, light weight is only of minor benefit.
On the other hand, if you are at 300mm f/2.8 with (say) a 7D II, for the same framing you can go to 400/2.8 on an FX or APS-H body and effectively gain another stop. Let's put that another way in case it isn't clear. In half-decent light, you can get away with a not-quite-long-enough lens by using a pixel-dense camera body on it. If you have (say) a 5D II and a 60D, the smaller-format camera will put more pixels on the bird and effectively give you more focal length. But the price you pay for those free "extra millimetres" is sensor noise. At ISO 400 you can afford it. If you are already at 1600 ISO, you can't.
This makes the 400/2.8 a clear best choice for rainforest, followed by the 300/2.8, leaving all the f/4 lenses well behind, and the f/5.6 zooms nowhere. (I've used a 100-400 in rainforest and even got a few good shots with it. But it's really not a suitable tool for the task.)
Conclusion: Clearly the 400/2.8 II, or at least the 300/2.8 II. Nothing else comes close.
SMALL BIRDS
The Achilles heel of big telephoto lenses is minimum focus distance. One of the very best things about the old 100-400 is that it focuses down to 1.8 metres. At 1m MFD, the new 100-400 is even better, as is the 70-300 at 1.2m. Of the bigger lenses, both the 200-400 and the 300/2.8 II focus to 2m, which is excellent.
10: 200-400 (2m)
8: 400/2.8 II (2.8m); 300/2.8 II (2m); 100-400 II (1m);
7: 100-400 (1.8m)
5: 70-300 (1.2m)
4: 500/4 II (3.2m); 400 DO (3.3m)
2: 600/4 II (4.5m);
1: 500/4 (4.5m);
In practice, the great divide for this task is whether you need a close-up ring or not. If you are settling down for a good session at a watering hole on a hot day, fitting a close-up ring is no hardship. On the other hand, there are few things more frustrating than spending hours trying to get within 10 metres of a special bird only to have it flip up onto a branch 3 metres away to have a good look at you out of each eye in turn while you stand there holding a lens that won't focus closer than 4.5 metres knowing perfectly well you haven't got a snowball's hope of changing lenses or putting a ring on before it flips off into the shrubbery again.
Conclusion: the 200-400 wins by a mile. This is probably the perfect small bird lens. Also noteworthy are the two f/2.8 lenses, both of which go quite close and focus very fast indeed; and the three small zooms (which score lower in my book despite their excellent MFDs because they are slower, and small birds move fast).
LANDSCAPES
Medium-long lenses are fantastic for landscapes. Every proper lens manufacturer of the planet makes at least one 70-200. Canon make four different ones and Nikon three. Curiously enough, I have never owned one. Instead, I use the long end of my 24-105 and the short end of the old 100-400. In this role, I'd prefer a 70-300, but the old faithful 100-400 does the job.
10: 70-300
9: 100-400 II
8: 100-400
4: 200-400
2: 300/2.8 II
1: 400 DO; 400/2.8 II; 500/4 II; 500/4; 600/4 II
Captain obvious can see the answer to this one.
Conclusion: any of the small zooms, or a 70-200 if you have one.
TOTALS
Having looked at these various use cases, which lenses do the best overall? (Bearing in mind these tasks are the ones I use long lenses for (your use may be completely different); that the rankings reflect my likes and dislikes (yours may well be different); and that I have used only a few examples - while I can confidently guess what a 600/4 or even a 200-400 is like, I'm on much shakier ground with exotica like the 400 DO and also the 2.8s with big converters.)
Let's just add up the scores and see if that tells us anything. No - on second thoughts, while each of these use cases is important to me, they are not all equally important. Let's cross out the landscape category. Realistically, I'm always going to have a lens that does this: if not the 100-400, then a 70-200 or 70-300.
Also, there are four different categories for walking around and only one each for rainforest and in-car. That's going to bias results, so let's weight them.
What do I do most of? Least of? Off the top of my head, working from a car: 25%. Long walks, handheld: 5%. Long walks with tripod: 10%. Short walks, hand-held: 20%. Short walks with tripod: 20%. Rainforest: less than 10%, but it's something I particularly want to master, so call it 20%. Close-up: I do this quite a lot, but I can always just use rings. Let's ignore it.
By a miracle, these rough-guess proportions total led to exactly 100% first go! Let's use them.
We simply multiply the scores by the weighting percentage. (Expressing it as a whole number to save having decimals.) This produces scores for each lens out of a possible maximum of 1000. (Note that a 1000-lens wouldn't be the perfect birding lens, it would be my perfect birding lens - which is precisely the point, of course. If you want your perfect lens, do your own numbers. Only takes a few hours if you know how to use a spreadsheet. You've stood under a tree waiting for a bird to turn up for longer at a time than that.)
730: 500/4 II
720: 600/4 II
680: 400/4 DO II.
615: 400/2.8 II
600: 500/4
620: 300/2.8 II
555: 200-400/4
245: 100-400 II
225: 100-400
130: 70-300
Clearly, I should race out and order a 500/4 II. Yes?
Well, no. I already have an older 500/4 which is very nearly as good as a 500/4 II in all respects bar weight. A 500/4 II would be a major convenience, not really a game changer. Then there is the 600/4: it would certainly be a handy upgrade - but not a revolution. It too is best at the things the old 500 already does very well indeed. Who wants to spend $14,000 for a mere "handy upgrade"? Well, maybe $9000 if we consider the changeover cost. Just the same, I still dream about the weight of a 500/4 II.
Now we get to the interesting one: the 400/4 DO II. Set rainforest aside and it's the best or close to the best at everything the 500/4 is not so good at; and the things it is weakest at, the already-paid-for 500/4 does well. They're a matching pair. (It would match even better with a 600/4. If you wanted two lenses with cost no object, those two would be very hard to beat.)
But why not buy a 300/2.8? In many ways it's a sort of a poor man's 400/4 DO after all: a bit short, reasonably small and light, something you could carry all day. And it's the second-best rainforest lens. This looks very much like the most sensible thing I can do: keep the 500/4 and the 100-400, simply add a 300/2.8.
But then i think about lyrebirds and Logrunners and pittas and Bassian Thrushes and Pale Yellow Robins and I'd really like a 400/2.8 .....
Hours of work and 3000 words on, I'm still uncertain. Nevertheless, the exercise has been worth it: setting out the strengths and weaknesses of the candidates like this has given me a much clearer grasp of the key issues to be decided. I hope that some of what I've written will be of some use to you too, if you are thinking about big lenses, and I'd be delighted to read of your experiences and thoughts.