Until recently, owners of Nikon Z mirrorless cameras had no choice if they wanted to shoot with long telephoto lenses: They had to use an FTZ adapter and an F-mount lens. But this is slowly starting to change. Two of the first native Nikon Z telephoto lenses are both 400mm lenses: an f/2.8 and and f/4.5. Both lenses are unicorns that everyone talks about but no one has ever seen, but we managed to get both of them on a recent expedition to Ecuador. In this article, I’ll compare the lenses based on my side-by-side experience.
Although both lenses are 400mm primes, they have just as many differences as similarities. Two factors in particular account for the almost $11,000 difference in price between the lenses. The first is the difference in maximum aperture, with the 400mm f/2.8 S allowing in about 1.3 stops more of light than the f/4.5. The second is the built-in 1.4x teleconverter on the 400mm f/2.8 S.
Throughout this comparison, I’ll cover these differences and more, and explain how they give each lens its unique personality.
Table of Contents
Weight and Size
If you’ve ever photographed with any of Nikon’s earlier 400mm f/2.8 lenses, you’ll probably appreciate the relatively light weight of the new Z-mount version. At about three kilograms / 6.5 pounds, it is still not particularly portable, but it’s 850g / 2 pounds less than the prior Nikon 400mm f/2.8 E AF-S FL ED VR. Against even older generations, the comparison gets even more stark.
Moreover, the overall weight is not the only thing that matters, but also the distribution of it. The Nikon AF-S 400mm f/2.8 G ED VR (two generations back) was notorious for having a large portion of its weight on the front of the lens. Shooting handheld required really strong muscles and nerves. This deficiency was to a great extent remedied by its successor, and has been pretty much solved by the current model. Although the Z 400mm f/2.8 lens requires a tripod for time-consuming work, shooting handheld is no longer such a pain. With the Z9 mounted, the center of gravity is at about the point of the tripod collar.
As for the 400mm f/4.5 lens, compactness really applies here. The weight of 1,245g is 195g less than the NIKKOR Z 70-200 f2.8 S VR. Even the renowned featherweight Nikon 500mm f/5.6E PF ED VR is 215g heavier! If we mount the TC-1.4x Z teleconverter on the 400mm f/4.5, the weight is identical to the 500mm f/5.6 PF (okay, 5 grams / 0.01 pound heaver), and the lens is now a 560mm f/6.3. So in terms of weight and its distribution, the 400mm f/4.5 can be rated very high.
Lens Build
Durability
Both lenses are part of the premium S-class lens series, and they both have good resistance against harsh handling and harsh weather. According to Nikon, the lenses are sealed against dust and water droplets.
With this in mind, I did not seek shelter any time that rain started in the tropics, but continued working. The sealing did a great job and water did not get into either lens. If I had to resist a real tropical monsoon, I’d still reach for a lens raincoat. The fluorine-coated front element is one of my favorite innovations in some modern lenses, since it makes it much easier to remove any stray droplets of water that land on the front of a lens.
The mechanical durability of both lenses filled me with confidence. Not that I subjected the lenses to any deliberate torture, but there is no shortage of occasional knocks against a tree or the ground when moving in the field.
I do have one minor complaint about durability, though. Nikon has changed the tripod collar locking mechanism, which has resulted in two things. First, tightening with a small amount of force fixes the lens reliably in the collar. But second, if you regularly use more force (AKA as much as it used to take on previous Nikon telephotos), the relatively delicate mechanism can be damaged. This happened to the 400mm f/2.8 during my tests. It was not expensive to replace, but even so, I made sure to tighten the lens more gently in the future.
Tripod Collar
Let me talk about the tripod collar a bit more. On the bright side, the tripod foot of both lenses now has two threads at the bottom for a tripod plate, which allows for a more secure attachment of plates. That’s it for the pros.
As for the cons, why can’t Nikon equip their lenses with an Arca-Swiss compatible tripod collar? If it would increase the price of the lens, I am willing to accept that price, and I think most wildlife photographers are in agreement.
Another ergonomic oddity is that the cover for the Kensington lock constantly kept falling off on my copy of the 400mm f/2.8, where it would dangle by the plastic safety strap. Maybe there are sports photographers who attach their $14,000 lens to a desk leg? But in the field for wildlife photography, I would have taken a knife to the cover on day one, if I hadn’t been borrowing the lens.
My last complaint about the tripod collar concerns the 90-degree indication. Both lenses have a small dot to align the tripod collar for horizontal or vertical shooting – but neither lens has a little click to ensure that you’ve aligned it optimally. I can understand that the cheaper of the two lenses doesn’t have it, but why is it absent on a $14,000 lens?
Lens Hood
The Nikon Z 400mm f/2.8 TC VR S lens is equipped with a one-piece lens hood, just like its last F-mount predecessor. It may lack the handsome carbon pattern of some other exotic Nikon telephotos, but I have no reason to doubt its durability. Its replacement price of $1,071 suggests that sufficiently durable materials have been used, at least (or that lens hood economics have some major flaws). It locks on with a traditional screw-lock mechanism.
Meanwhile, the replacement cost for the 400mm f/4.5’s lens hood is $98, which is great considering that I almost lost mine at one point while machete-ing my way through an unmaintained trail. (Thankfully, I didn’t have to backtrack far to find it after realizing that the lens was shorter than usual.) It’s not that the lens hood is badly designed, but turning it sufficiently hard will release it, despite the locking mechanism. So, this is one area where I’d give the 400mm f/2.8 a small advantage.
Controls
Both telephoto lenses are quite complex devices in terms of controls, allowing a wide range of fine-tuning possibilities. On the 400mm f/2.8 alone, we find a total of three rings – which is more than is found on most zoom lenses. Add to that a number of buttons and a couple of switches. The 400mm f/4.5 is a bit less complex, but still full of controls. What purpose do they serve?
1. Rings
The Nikon Z 400mm f/2.8 TC VR S has three control rings, and the Nikon Z 400mm f/4.5 S has two.
With the 400mm f/2.8, I set the control ring to quickly change ISO when shooting in full manual mode. Then there’s the focus ring, which can be programmed for non-linear or linear response on the Nikon Z9. As for the new function ring (which is missing on the 400mm f/4.5 S), it’s an interesting bit of ergonomics. When you twist it to one side, you can set or recall a focus distance. When you release it, the ring snaps back to the middle and returns your focus distance to where it was before.
On both lenses, the individual rings are easily distinguishable from each other by touch. That’s important for controlling them with your eye at the viewfinder.
2. Buttons
Each lens has a whopping six buttons on it. First, there is a programmable L-Fn button on the left rear of each lens. Then, a button on the opposite side can store focus distances in the camera’s memory. To recall this preset distance, both lenses have four memory recall buttons spaced at 90-degree intervals on the front of the lens barrel.
Personally, I see the combination of the Memory set and Memory recall buttons as a big advantage of professional lenses. I use these buttons most often when photographing birds in controlled conditions, i.e. hummingbirds in flowers for example. I save the position of the flower in the camera, and if the autofocus misses the hummingbird and focuses far beyond the flower, one press of the memory recall button puts me right back in the game. When shooting from a tripod, I keep one finger on one of the front buttons at all times.
Another situation where this feature can come in handy is when photographing birds in flight. You pre-focus on the distance where you expect the bird to fly and store it in memory. When the bird starts to fly, you press the button and have a fighting chance at capturing the bird in flight in the spot you want.
There are other ways to set the Fn2 button(s) on the front of the lens, which I don’t recommend on the 400mm f/4.5, but could be worthwhile on the 400mm f/2.8 S. That’s because on the f/2.8 lens, you can use the new function ring to recall focus distance instead. One option is to set these buttons to enable Dynamic-area Small or Single Point AF mode, for cases when the subject-detect autofocus fails to detect the subject’s eye.
3. Switches
Compared to the five switches on the previous generation 400mm f/2.8, there are only two on both of these newer lenses. What are we missing? There’s the vibration reduction switch (with off/normal/sport options), the front button mode setting, and the switching of silent autofocus versus the beep.
To change the vibration reduction/IBIS mode, you now have to go into the camera menu. Personally, I have this item under the i button. However, I use sport mode almost 100% of the time. What makes me do this? Although normal mode should provide greater stabilization performance, the image twitching in the viewfinder when using long telephoto lenses disturbs me.
I don’t miss the other two switches either. The front button functions can be assigned in the camera menu and aren’t something you’ll change very often anyway. As for the autofocus confirmation beep, that’s not even possible in AF-C mode, which I use almost all the time. And even in AF-S, it’s annoying anyway.
What is left on both lenses are dials for switching between auto and manual focus – also not something I change very often – and the focus distance limiter. This one, I actually use! On both lenses, this offers FULL and “∞ to 6m” ranges. If you know that you are not going to get closer than 6 meters / 20 feet to the animal you are photographing, it is useful to communicate this fact to the camera to speed up the autofocus function. It really works.
Autofocus Speed
Considering the mass of glass inside both lenses, especially the 400mm f/2.8 S, Nikon faced a difficult task designing a motor that would focus as quickly as possible. The resulting Silky Swift VCM (that’s the official name) uses magnets instead of gears to focus. Its power literally radiates from the 400mm f/2.8; Nikon has issued a warning for users with pacemakers, where the strong magnetic field emitted by the motor can cause problems.
How did the 400mm f/2.8 focusing work in the field? In a word, flawlessly. When using adapted F-mout telephoto lenses (especially the 200-400mm f/4.0 zoom), I struggled with the lens oscillating between two “close” to accurate focus positions, like it couldn’t choose between them. This behavior isn’t present on native Z-mount lenses, including the 400mm f/2.8 S.
When the camera recognized the subject, the lens immediately and unerringly pointed straight to the correct plane of focus. There was no “a little forward, a little back, then take the shot.” (If you have experience with older cameras, you probably know what I’m talking about.) When the camera didn’t recognize the subject, that’s when the memory recall button/function ring came into play.
Unlike the 400mm f/2.8, the 400mm f/4.5 works with a pair of stepping motors. When you attach both lenses to a tripod in the silence of the forest and activate the focusing, the f/4.5 lens makes a bit of noise. You have to put your ear very close, though, because both lenses are very quiet indeed. Sometimes, I had to make sure with my hand placed in front of the lens that they were actually focusing.
But this slight difference in volume was about the only difference I observed between them in the field. I tried focusing manually at the minimum focusing distance and then automatically on the trees in the background. The difference in speed, if any, was beyond my eyes’ resolving power. Both lenses simply focus very quickly. So, good news to photographers on a budget: You aren’t losing focusing speed with the f/4.5 lens, at least assuming that there’s enough light to focus with both lenses in the first place.
Pleasingly, even the built-in teleconverter on the 400mm f/2.8 did not cause a noticeable drop in focusing speed. In fact, quite the opposite. As the subject in the viewfinder became 1.4x larger, it became clearer to the camera’s intelligence, and with it, the confidence of the autofocus increased.
Usability with Teleconverters
This is where the 400mm f/2.8’s greatest strength lies. Its wide maximum aperture provides enough light to use up to a 2x teleconverter very comfortably. But the real game-changer is the integration of a 1.4x teleconverter directly into the lens body. If you pay the hefty $14,000 for this lens, you can retroactively rationalize your purchase by saying that you actually bought two lenses – a 400mm and a 560mm.
I really enjoyed the built-in teleconverter. If there was anything my Sony or Canon colleagues envied in the field, it was the lever that I used to add the teleconverter to the lens’s optical system in a split second when needed. The speed at which the teleconverter can be enabled is evidenced by the fact that I was able to photograph a hummingbird feeding on nectar at both 400 and 560mm focal lengths in a single sequence.
But sometimes the built-in 1.4x teleconverter is not enough, and then the option to extend the focal length by 2x comes in handy. After previous unsatisfactory experiences with the 2x teleconverter on the old 400mm f/2.8G, I was a bit skeptical at first. But after my first attempts with the Z teleconverter TC-2.0x, my skepticism was gone. The photos were sharp and with good contrast. Even the autofocus did not suffer noticeably from the converter. At the maximum aperture of f/5.6, it is still very usable.
The last possible way to ensure maximum range in situations where the subject cannot be approached in the field is a combination of two teleconverters. I realize that this sounds almost heretical, but I’ve tried it and will be happy to share the results with you. If you put a 2.0x teleconverter between the body and the lens, while activating the built-in 1.4x teleconverter, the resulting focal length of the setup is 1120mm with a maximum aperture of f/8.
I would really only use this setup in exceptional situations, but it’s good to know that it can be counted on. It even lets in more light than the 400mm f/4.5 with just the 2.0x teleconverter (which becomes an 800mm f/9)! The autofocus still works on the double-teleconverter combo, although it loses some speed on moving subjects. Also, the sharpness of the lens is starting to suffer a bit, even though it’s still within acceptable limits.
At 1120mm, a more fundamental problem is the mass of air between the lens and the subject, with a major loss of sharpness from atmospheric distortion. This can be an unsolvable problem.
To sum up, I can transform the 400mm f/2.8 lens to 560mm f/4.0, 784mm f/5.6, 800mm f/5.6, and finally 1120mm f/11.0 with the use of currently available teleconverters. At that point, even a prime lens appears to be a versatile tool on par with zooms.
With the 400mm f/4.5, the situation is somewhat different. Only the 1.4x teleconverter is easily usable with this lens (making it a 560mm f/6.3). However, I took the images for the Spectacled Bear article using this lens in combination with a 2.0x teleconverter. I have no major reservations about the image quality of the photos taken this way, but the maximum aperture of f/9.0 is too slow for many subjects. Even during the daytime, my ISO was around 10,000 with this combo much of the time.
Optical Characteristics
Sharpness and Contrast Transmission
Without the hard data obtained from lab tests – which my colleagues Nasim and Spencer are eagerly planning to do once they get copies of these lenses – take my words below as my feelings based on sample photos and experience in the field. Still, that feeling is excellent in the case of both lenses being compared. I dare say that in terms of sharpness and contrast transmission, the real-life performance of both lenses is identical, or close enough to make no practical difference even with a 45-megapixel camera.
So why pay $10,750 more for the 400mm f/2.8? At that point, every third of an f-stop costs us $2687.50! That seems a big price to pay for four clicks of the aperture control dial. However, those who spend money on such lenses know that those four clicks will allow them to shoot in conditions that might already be over the edge for slower lenses. (The convenience of the built-in 1.4x teleconverter cannot be denied either.)
If that still sounds crazy to you, you may want to read my article on the value of fast telephoto lenses.
Chromatic Aberration
It wasn’t easy to make an image where the chromatic aberration was visible on either lens. Still, I think I managed to do it in some photos of Long-Wattled Umbrellabirds. Here’s the worst-case scenario with the 400mm f/2.8:
For the photo above, I had to use the built-in teleconverter and strong exposure compensation of +2 EV. Then I had to shoot it against a gray sky in bad lighting conditions. Only then did I get some thin purple lines along the edges of the bird and some of the leaves. Out of approximately 15,000 photos taken with this lens, this is one of only two instances of visible chromatic aberration that I have registered with the 400mm f/2.8.
With the 400mm f/4.5 lens, I only encountered chromatic aberration in the photograph below of a Collared Arassari flying against a cloud-covered sky. And you probably won’t be able to notice it at web resolution anyway:
I searched the edges of the wings at 200% magnification and there it was! There is a faint purple line running along the front edge of the wings. In all the other photographs I searched for signs of chromatic aberration in vain.
By this, it may seem that the 400mm f/4.5 actually performs better in chromatic aberration, but keep in mind that there’s no 1.4x teleconverter here. The two lenses are probably about the same, and only when introducing a teleconverter to the equation (even the built-in one on the f/2.8 lens) is there even the slightest chance of noticeable CA. It’s not a concern for either lens.
Flare Resistance
For the 400mm f/4.5 lens, Nikon has used the proven Nano Crystal Coat, while its flagship telephoto lens features the brand new Meso Amorphous Coat. For the latter, Nikon promises that it “provides the highest anti-reflection performance in NIKKOR history.” Unfortunately, I was unable to test the lens in severely backlit situations, as I encountered much more rain than sun on my trip to the tropics.
When the sun did briefly show up while photographing hummingbirds, I had the 400mm f/4.5 lens mounted. The remnants of sunlight were no challenge for this lens; I couldn’t create any loss of contrast or flare even when backlit. Since the 400mm f/2.8 S supposedly has even better coatings than this, I fail to see how backlighting could be an issue with either lens.
Shortest Focusing Distance
It’s a clear tie here. Both lenses have the same close-focus distance of 2.5 meters, which is a very pleasant value (8.2 feet). This is a bit better than the 400mm f/2.8 DSLR lenses, which were 2.6 or 2.9 meters depending on their generation. With the older lenses, I sometimes needed to reach for extension tubes for small hummingbirds, which is no longer an issue.
Optical Stabilization
Both lenses play an even match here again. At least according to the manufacturer’s claims, both should be able to shoot shutter speeds up to 5.5 stops longer than similar lenses without stabilization. Synchro VR, which is only available with the Nikon Z9, can round that value up to 6 stops.
In practice, this means we should be able to hand-hold shutter speeds somewhere around 1/8 second. This is assuming, of course, that we use VR in Normal mode. While this is slightly more powerful than Sport mode, sometimes you press the shutter and see the viewfinder image twitch like someone kicked a tripod. I use Normal mode much more for shorter focal lengths where this effect is not so noticeable, not for telephoto lenses.
With both lenses set to Sport VR, I achieved sharp results with speeds around 1/30 second. The thing to keep in mind here is that the camera and lens can largely eliminate your vibrations, but not the vibrations of the creature you are photographing. So, fast shutter speeds are still highly recommended for almost any type of sport or wildlife photography.
Bokeh
If I had to name one lens that can whip up a disturbing thicket into a fine cream, it is the 400mm f/2.8. Maybe it’s a bit of a crutch to shoot like this, but so what? The 400mm f/2.8 can clean up (almost) anything distracting in the background with the f/2.8 aperture.
With the cheaper 400mm f/4.5, you have to take into account that the f/4.5 aperture reveals a bit more about the character of the background. On the other hand, you get a bit more depth of field. And because you’ll be shooting wide open at f/4.5, the light spots will be beautifully circular at that aperture, just like in a Hollywood romance movie.
Between the two, the 400mm f/2.8 wins, but more by virtue of the aperture itself than anything different about the character of the bokeh. But I leave you to look at the images throughout this comparison and make your own judgement.
Summary
If I were to summarize the differences between the two lenses in one sentence, it would look something like this: The two lenses are surprisingly close in optical quality. If you lose anything with the 400mm f/4.5, it’s so small that it doesn’t matter to photos in the field. Instead, the biggest differences are in the fundamental specifications: 1.3 stops of light between them, 1705 grams more with the f/2.8 lens, and of course $3250 versus $14,000.
Then there’s the built-in teleconverter. To me, this is almost as big of a selling point as the f/2.8 aperture. The possibility to insert a teleconverter in a split second is really very addictive; it makes the 400mm f/2.8 as convenient as a zoom. Attaching a teleconverter in the traditional way takes many times longer, which often means you’re not using it when you should be – or using it when you shouldn’t.
But the light weight, compactness, and price of the 400mm f/4.5 by comparison are hard to ignore. Considering that it has no real optical compromises compared to the f/2.8 lens, this is definitely the one I’d get if I were on a budget. The lens is so good that I have to look at the EXIF to recognize which lens was used to take which photo.
Any negatives of the two lenses? None to speak of. Nikon has refined the design of telephoto lenses to an art form. By far the biggest risk of both lenses is that if you try one, you won’t want to return it.
Price and Availability
The Nikon NIKKOR Z 400mm f/2.8 TC VR S lens can be purchased for $14,000 – or rather, it can if it’s in stock. At the time I’m publishing this article, it’s unavailable, and you’ll need to put your name on a waitlist.
Meanwhile, the Nikon NIKKOR Z 400mm f/4.5 VR S lens is $3500 and suffers the same problem of unavailability. It’s time to make like the Count of Monte Cristo – wait and hope!
I love your many articles AND the hummingbird photography in particular!
For the latter, I’ve used both a D850 and now a Z8 (with the Eye-detect software), using a really sharp AF-S NIKKOR 300mm f/2.8G ED VR II with a TC-14E III and the FTZ-II.
Since the camera focuses with the lens wide open, I get great fast-focus & -tracking and have captured hummers close-enough without having to post-process too much (closest focusing distance is 7.2 – 7.5 feet (call it 2.3 meters)…And of course the built-in DX mode gives me another bump-up when necessary.
For me, it’s portable (or I put it on a monopod, at times with a small ballhead on it), and I personally like the weight of the combination as I handhold it.
‘Saved me a lot of $$ too !!!
how are you editing these pictures in the review
Great Article….
Just FYI, two 1.4 TCs stacked would give you 800mm, not 784mm. A 1.4 TC is actually 1.4114 (square root of 2). So 2 of them stacked end up being 2X. 1.4 is just the rounded figure.
“As for the cons, why can’t Nikon equip their lenses with an Arca-Swiss compatible tripod collar?”
Not everyone has or uses Arca Swiss compatible mounts. Many use other manufacurers such as Manfrotto (in two different sizes I believe) and no doubt other manufacturers out there have their own proprietary system. I have found Manfrotto’s beefier mounts/plates stronger than Arca Swiss and more capable of taking heavier lenses, etc., as good as Arca Swiss are. I use both mount systems for different jobs.
Nikon and others have the sense to take the universal path.
I’ve used a 300mm f2.8 GII for a number of years and have always been impressed with it’s quality and smooth backgrounds. I’m now using the Nikon Z8 and Z100-400 4.5 – 5.6. Results are also excellent but the backgrounds are not as smooth and creamy as the 300mm with FTZ and with or without a teleconverter. Even if I could afford the 400 2.8 I couldn’t get it because I have a pacemaker. I’m wondering if I should sell/trade my 300 2.8 and get a 400 f4.5. Looks to me from the images in your article that the backgrounds are pretty good.
The 300mm f/2.8 is a lens that is hard to compete with. Like the 400 f/2.8 lens. Other lenses may be similarly sharp, but the bokeh that these lenses are capable of is exceptional. However, under the right conditions you can get a similar look from less premium glass. the 400mm f/4.5 is one of them. If you have the opportunity, I recommend giving this lens a try. Especially with smaller birds that need to be photographed at shorter distances, you can get a nice creamy bokeh similar to that of the 400mm f/2.8.
The 400mm f/2.8 lens at 7.1 lbs weighs 4.4 lbs more than the 400mm f/4.5. The 4.5 can be hand held but the f/2.8 lens needs a tripod to both support its weight and to be able to reach the control buttons on the lens which cannot be done while supporting the lens with one hand.
Of course, the 400/4.5 is a hand held king. But even the f/2.8 version is not unusable in this respect. On the contrary. But I am influenced by my experience with the f/2.8 G, which was more than 1.5kg heavier. After this monster almost every lens is light.
Lovely review and truly excellent photos Libor, thank you.
It occurred to me whilst reading about all the teleconvertor options, that in addition to those, you can also utilise Nikon’s DX mode to gain even more focal length options with a few presses and clicks of the i and OK buttons.
Thank you Charles, I’m glad you enjoyed the review.
You are absolutely right about the DX mode. However, since I always edit photos on my computer, I don’t use DX mode. When I can, I shoot so that I don’t have to cut in post-production. But DX mode doesn’t give me more pixels per bird, instead it increases the risk that the subject won’t fit in my viewfinder. It spreads its wings and it’s out. That’s why I generally shoot in FX and eventually cut later.
If your camera is just off by 0,1°, then that can be tricky to correct if you have a click that fixes the lens at 0,0° and makes it difficult to set the angle at anything smaller than 0,5°.
Good point, Chris.
Hi Libor, Thanks for this review.
I’d really like to know how the 400/4.5 compares to the 70-200/2.8 w 2x @5.6. I’m not often at 400mm, but having recently returned from Okavango Delta where I used the 100-400, was less than impressed with that lens. It is very very good, but short of the excellence of the 70-200. Wondering how much excellence survives with the 2xTC compared to the 400/4.5? No doubt the dedicated prime is superior, but for someone who is not usually shooting at such lengths but is looking for “excellence” how big is the gap?
Thank you for asking, Matthew. I don’t have the hard data to back it up (Spencer will be working on that soon, I’m sure), but my impression of the lens is great. If you found the 400mm soft, I’d say it’s not the lens that’s at fault, but Africa itself. After all, taking a sharp photo in full sun on an African safari is a challenge even for a lens like the 400mm f/2.8. The mass of warm air between the elephant and the camera kills the sharpness of any telephoto lens not long after sunrise.
I dare say the 70-200 with a 2x teleconverter would be no better.
Very good comparisons, Libor! Good work :). The 400 f/4.5 is a very enticing options for lightweight bird photography and the 1.4X TC looks good on it. I think a lot of people who were previously afraid to use TC’s on DSLRs will be very happy with them now, at least the 1.4X — the 2X still leaves me doubtful.
I think it will be a very in the upcoming years when Nikon releases their 200-600 and 600 f/4 — then the question will be which one of these is best for the bird photographer! Previously the 400 f/2.8 was not the best option but with the built in TC it’s in the game now.
Just like you wrote, Jason. I used to find 400mm on full-frame a bit short for bird photography. The current model has changed my view of that focal length.
As for teleconverters, 1.4x on the 400mm f/4.5 model is the obvious choice. The 2.0x teleconverter I would only seriously use on lenses with a maximum aperture of f/2.8, where it works great.
I’m waiting with great anticipation for a pair of 200-600 and 600/4 lenses. If the former were at the long end of f/5.6, it would be great. Personally, I think it’s more likely to be f/6.3 (and we’ll be glad for that). If the 600/4 has a built-in teleconverter, it will be an incredible lens for birds.