Canon 400mm f/2.8 III vs 600mm f/4 III

robamy wrote in post #18852887
Sorry I should have mentioned that. I use the 1Dx Mark II. I am talking about AF. You can set the focus limiter, or manual focus to get the best results but out of the lenses I have used in the 800mm range, the 400mm DO II struggled a bit. Do not get me wrong, it is an awesome lens and is great for stationary at 800mm and with the 1.4x it is outstanding. It is my wife's most use lens and it performed well in Costa Rica for me last year but vs the 400mm f2.8 Mk III at 800mm the speed of AF is not in the same league.

Well, I would expect it to be not quite as good as the 400/2.8 III, because that's f/8 as opposed to f/5.6, and the 400/4DO II seems to be sharpest wide open, which is good, but the 2.8 III is probably also sharpest wide open, so even sharper by a small amount. There's a big difference between OVF PDAF at f/8 and f/5.6, even if some cameras are better at f/8 than others (my 7D2 requires pretty ideal conditions to do its f/8 centerpoint AF with any kind of speed or without hunting). There seems to be an unwritten rule that OVF PDAF ability falls off of a cliff, rather than gradually degenerates, at some point, depending on the body. The 7D2 will not do OVF AF at f/11 no matter how much time you have; it will hunt endlessly, and/or park at some offset that can not be addressed by MFA. I have no combo that is f/10; f/9 works in good light and contrast, but can't make big changes in focus distance quickly. The 1DxII is a bit better at f/8, but it falls off of a cliff, too, because I have heard no reports of it working at f/11, even slowly. I've queried if anyone ever got f/11 OVF AF with the 1DxII, and no one ever comments. The various cameras seem to vary greatly in how good they are at f/8, but all seem to be useless at f/11, maybe f/10 even, but there aren't a lot of combos that give f/10 to tell.

OVF AF ability is the Achilles heel of high-magnification DSLR photography, IMO. It can work very well in good light and with optimal open f-numbers, still unmatched by mirror-less for AIServo with auto point selection in good light with erratic subjects, but it is really crippled with high f-numbers, where it is not just slower, but impossible.

I'd be using a 1DxII instead of the 7D2, but the fact that the needed f-ratio to accommodate tele-conversion suitable for my pixels-on-subject taste knock the 1DxII down in AF ability. My subjects are small and distant, mostly, and I would not take advantage of the larger sensor very often. I think "lens first", and I chose the 400/4DO II because it is about as heavy as I wish to carry all day and on public transit, and is very sharp (but renders out-of-focus tiny points of light very poorly), and a 20MP FF is not going to get me maximal pixels-on-subject with usable AF, and each TC does add at least a very small degradation of its own, and two stacked may be worse yet.

Where is my 450MP FF camera with advanced AF? That's the solution to all these compromises, if the bandwidth and data load could be handled or tolerated. No TC is likely needed because of pixel density, and less unintended crops from subjects that jump out of the frame, with the larger sensor. I once thought that the future was coming soon, but the future is starting to look very far off. What really sucks about owning a Pentax Q and adapter is that I can see what the 12MP center crop of a 450MP FF camera would look like with my 400/4DO II, and it is amazing the detail that can be captured, at least in a narrow plane of focus, with adequate stability. I'm sure that the 400/2.8 III would make even better use of such pixel density.

Canon's Big white lenses are way, way ahead of their sensors.

John Sheehy wrote in post #18853186
, and I chose the 400/4DO II because it is about as heavy as I wish to carry all day and on public transit, and is very sharp.

These and the cost are the biggest pluses of the 400mm DO II...

Tempting deal on 600mm on watchdog site.

rndman wrote in post #18853417
Tempting deal on 600mm on watchdog site.

They've gotten rid of the early adopter fee

Firstly a little background. Up until summer last year I owned 500 f4 mk1 (used an abused for 4 or 5 years), 600 f4 mk1 (bought used) and 200-400 (bought new and used for 4 years). The 600 was a beast but as sharp as any lens I have ever owned, but often too long, and too heavy to use for travel. The 500 f4 was my go to travel lens but shooting locally in the winter I often found myself with no light, and wishing for f2.8 (seriously the difference between ISO12k and 6400 and ISO3200 is pretty big). The 200-400, although a great lens never quite lived up to the hype. For my shooting the focus breathing at under 10-15M was a huge disappointment (but it is a great travel lens). As I was using it mostly at 400mm+ anyway I tended to use the 500 more often.

In the end, knowing what I shoot most often and what I am likely to shoot I decided to sell all three (the 500 and 600 were bought at a great price and were sold at a profit, which obviously made the decision easier) and buy the 400 2.8 mkII. Weight wise it sits around the 500 f4 and is barely heavier. Takes both 1.4 and 2x TCs perfectly, seriously good wide open. Takes up a little more space in my bag.

So I have 400, 560 and 800mm covered. My 100-400 mkII covers the rest.

Any regrets so far? Nope. Would I like the mkIII version. Yep

What do you plan to take photos of? The 400/2.8 is usually used for field sports, and the 600/4 is for wildlife and birding. If you want flexibility, then I suspect the 400 is a better choice.

frankchn wrote in post #18856796
What do you plan to take photos of? The 400/2.8 is usually used for field sports, and the 600/4 is for wildlife and birding. If you want flexibility, then I suspect the 400 is a better choice.

Wildlife (mainly birds) only. No Sports.

rndman wrote in post #18856843
Wildlife (mainly birds) only. No Sports.

I would take the 600/4 and maybe pair that up with a 100-400 for closer / larger wildlife?

For birds, 600 all the way.

Always with the caveat, that you buy the focal length for the subject + setting you are shooting. If you're shooting in a pre-staged setting with feeders and the birds come to you, you may not need 600, and the 400 will suffice. If you are in the field and realize you need all the reach you can get: 600 and TCs. I've debated this very same question myself over the past few years, and I'd rather not need to rely on a 2.0x TC to get to my preferred focal length.

Tell you what though, if Canon were to release a monster 7DIII (with improved noise control), I'd probably drop down to the 400 III.

We can all hope for this. I have the sinking feeling that Canon has caught a bad case of the mirror-less bug.

MatthewK wrote in post #18857035
For birds, 600 all the way.

I've debated this very same question myself over the past few years, and I'd rather not need to rely on a 2.0x TC to get to my preferred focal length.

I agreed with this for years, that is why I had the 800mm f5.6 for many years, until the new 400mm Mk III, it has been just stellar with the 2x. I have been shooting in low light lately due to the poor weather and the 2x is just not missing, locking on very nicely. I would suggest to anyone to try the 400mm Mk III before it is dismissed because of the TC use. Even my 600mm had the 1.4x glued to it for the most part. We have amazing glass to pick from today, not easy just picking one.

robamy wrote in post #18857668
I agreed with this for years, that is why I had the 800mm f5.6 for many years, until the new 400mm Mk III, it has been just stellar with the 2x. I have been shooting in low light lately due to the poor weather and the 2x is just not missing, locking on very nicely. I would suggest to anyone to try the 400mm Mk III before it is dismissed because of the TC use. Even my 600mm had the 1.4x glued to it for the most part. We have amazing glass to pick from today, not easy just picking one.

Yeah, 95% of the time I'm at 840mm using the 600 + 1.4. If I'm out with the 80D though, it's bare lens all day

MatthewK wrote in post #18857790
Yeah, 95% of the time I'm at 840mm using the 600 + 1.4. If I'm out with the 80D though, it's bare lens all day

Smaller pixels are optically superior to a TC, but a TC is usually still superior to cropping (especially with larger pixels), if AF performance is satisfactory.

Not doubting you at all, but do others find this to be true, too...that a crop body is better for additional reach than a FF with 1.4x TC? I know the crop body has the 1 stop of light advantage which can be huge. If true I might pick up a 7D2 for my 100-400.

birder_herper wrote in post #18858304
Not doubting you at all, but do others find this to be true, too...that a crop body is better for additional reach

Crop sensors in and of themselves do nothing of value; higher pixel density often exists with the smaller sensor, and that is its real value for focal-length-limited photography.

There is no light advantage. The entrance pupil of the lens determines the total subject light ("duck photons") per millisecond. The TC does not change the subject light; it just spreads it out over a greater area.

What does vary with a TC is the open f-ratio, and f-ratio is extremely significant for AF, especially phase-detect AF, and more especially, OVF/DSLR phase-detect AF. These problems have a lot more involved than the amount of light; it is the geometry of light which forms the hardest limits, and geometry is determined by f-ratio. You could switch from an f/5.6 optic to f/8, and even quadruple the amount of ambient light, and the AF may still deteriorate, because it is not just the amount of light.

So, it isn't good enough that a larger-sensor camera is better than a smaller-sensor one at a given open f-ratio, if you're not using the same f-ratio to get an equivalent number of pixels-on-subject ("duck pixels"). It must be better at a very similar pixels-on-subject to be practically better.

I remember when people were talking about the AF on the 5D3 being better than the 7D2 in their opinion.

What does that actually mean, though? If you are comparing at the same open f-ratio, then, yes, the 5D3 might AF better, but if you throw a 1.4x on with the 5D3, to approach (but not quite reach) the same pixels-on-subject, then the 5D3 is f/5.6 when the 7D2 is f/4, and the 5D3 f/8 when the 7D2 is still at f/5.6, which works with all AF points, and fairly well, and the 7D2 is operating at half the ISO with the same shutter speed, so the fact that the 5D3 has more noise than the 7D2 at a given high ISO is irrelevant. When the 7D2 is at f/8, where it still has less-than stellar center-point AF, the 5D3 has no OVF AF at all at f/11.

The 5D4 improves on the 5D3 withpixel density, and the 1Dx series with faster lens drive, of course, but we still need to consider the AF in terms of normalizing practical final-image results; not "at" a specific f-ratio.