6D autofocus capabilites: let's bust some myths about it

[3kramd5]

Its not really comparing apples with oranges because the Eg-S allows you to see in the viewfinder more accurate DOF - even when autofocusing - than the 5D3's stock screen which is not user replaceable. 5D3's fixed focus screen only shows about f/2.8 DOF while the Eg-S on the 6D will come close to the DOF of f/1.2.

So, the fact that the 6D allows the user to swap to Eg-S means that what you see in the viewfinder when both AF *and* MF will more accurately represent the end product. If you do choose to MF to that end product, it is worlds easier on the 6D using Eg-S vs the 5D3's fixed screen.

Yes, the 5D3 will likely allow to set up your shots faster, but that does not make the 6D AF useless.

Indeed. The lack of replaceable focus screens is one of the annoyances of the 5D3 (cost being the primary annoyance). I can live with it, however. When I have the luxury of setting up my shot, I generally manually focus with live view.

I don't think anyone has said the 6D AF is useless. Thousands of photographers have used it for years with the 5D2 (no, they aren't identical, but for all intents and purposes one uses them the same way).

No, it's not useless. But it isn't even remotely like the 1Dx unit, or the almost 1Dx unit in the 5D3. Even in one-shot (which I use exclusively with my 5D2 and much of the time with my 5D3), having reasonably accurate points covering about 2/3 of the width of the frame allows for thin DOF AF with a much higher hit rate. And when you consider tracking, it's apples and paperclips.

I feel like the back button focusing isn't as reliable -or maybe I'm doing it wrong. Are you supposed to be holding the backbutton(what I've been doing) or just press it once? I'm shooting in AI Servo.

It's exactly as reliable. Whether you engage AF with the shutter release or the AF-ON button, what follows is identical.

If you're in Servo, you're doing it right: hold it down, including when you release the shutter.

 

[TeT]

my 6D focuses closer to my T4i than to the 5DIII I briefly used.

John

 

[Loswr]

Full size uncropped image. Autofocused with the 6D center point on the yellow bubble level, then recomposed. Apparently nobody else can do this, but my camera can while I'm bending over, and handholding it in a very dark room, at 1/13 second, f/1.8, 24mm, about 4 inches from the lens front element, with no image stabilization. It looked darker than this to my naked eye, and I don't think I used exposure compensation (the metadata doesn't show it if I did). Shot only as a jpeg, with some NR applied in LR. ISO 25,600.

What's all the fuss about focusing and recomposing? If little old me can do this, hand-held with no image stabilization, why can't others do it at 1/200 second in good light, or especially with strobes or flashguns? Not saying all lenses and focal lengths are the same...but gee whiz. It's not unheard of, because I did it.

The 'fuss' is that focus/recompose causes backfocus. It's simple geometry– the focal plane is flat (field curvature notwithstanding), and you're rotating the camera after locking focus, which moves the focal plane to a position behind the subject after recomposition. With a narrower aperture, the deeper DoF is often sufficient to mask the effect of the backfocus, but with a wide aperture, you'll see the backfocusing.

Frankly, your image of the ballhead is so dark and noisy that it's difficult to say anything is in sharp focus. But one thing that seems at least close to in-focus is the index mark on the left side of the clamp, and that's well behind the bubble level. That index mark is certainly more in focus than the lettering on the front of the clamp, despite that lettering being much closer to the bubble level. So if you did indeed successfully focus on the bubble level, then you've demonstrated (albeit poorly) the problem with focus/recompose.

It's not that 'nobody else can do this', but can ≠ should, and many of us know that focus/recompose causes problems with fast lenses shot wide open. If you're using a slower lens, stopping down your fast lens, or aren't a stickler for critical focus on your intended subject, focus/recompose can work.

 

[Loswr]

6D's AF capabilities and focus points are just plain sad for today's standards for a camera worth that much money and a FF label. Some people defend it by saying "it can take sports photos too!". Sure it can, I did it with my 550D also.

Agreed. I took sports photos with no AF at all, and I had to advance the film by hand between each frame. But the fact is the Rebel T4i/650D has an overall better AF system than the 6D - which, as you say, is just plain sad.

 

[Loswr]

To further add, my 1Ds3 and 1Dx never miss at f/1.4 on the outter points. Never. Always exact. No variability. Nails it everytime and that's even without AFMA.

it is physical impossibility because the AF measurement angle accuracy in Canons AF is F-2,8 ( eg.3,4)

That's not correct.

The specified precision is within the depth of focus at the max aperture of the lens for a standard precision AF point, and within 0.33 depth of focus (0.5 for some models) at the max aperture of the lens for a high precision AF point.

I discussed this issue with Chuck Westfall (Canon USA's technical mouthpiece), and this is part of his response:

"The fact that the AF points are functional with apertures as small as f/5.6, f/4 or f/2.8 respectively depending on the camera model and AF point under discussion does not imply that their measuring precision is limited to the depth of focus at those apertures. The AF detection system has the capability of calculating depth of focus based on the maximum aperture of the lens, whatever it happens to be."

 

[mackguyver]

This is what I'd love to see in a Canon body, especially with the 6D center point:
Hasselblad True Focus

 

[Loswr]

This is what I'd love to see in a Canon body, especially with the 6D center point:
Hasselblad True Focus

+1

The angular motion sensors are already there as part of the electronic level system, so automatic compensation for recomposition after locking focus is something that could be implemented should Canon choose to do so.

 

[Stig]

This is what I'd love to see in a Canon body, especially with the 6D center point:
Hasselblad True Focus

+1

that would be great

 

[Sporgon]

This is what I'd love to see in a Canon body, especially with the 6D center point:
Hasselblad True Focus

+1

that would be great

Another nail in the coffin of manual focus.

Seriously though, reference the 6D points being inferior to a much cheaper 650D, it's just inevitable if the concept of the 6D was to exist. Canon had to protect the 5D III. Remember that 5D II was 'crippled' with the 5D/20D focus system to protect the 1Ds. However it didn't work; 5D II's really ate into 1Ds sales, so Canon effectively said 'if you can't beat them, join them' and introduced the 5D III with full 'pro' AF and effectively dropped the 1Ds line. The 5D III is still much cheaper than a 1Ds !

Canon wouldn't want the 6D to do the same thing to the 5D line so they added plenty more 'crippling' features to be sure.

I'm not a Nikon expert but I'm guessing that Nikon wanted to sell as many D600's as they could given the cool response to 36mp, so they don't have the same vested interest in protecting the D800 line.

I still find the 6D a fantastic camera but when the time comes to change the 5D II I'm currently not sure if we'll get another 6D or a 5D III.

 

[ashmadux]

I dont understand when those that do not own the camera in question consider actual users/owners tp be 'whiners'.

Anyways...If you come form any body with reasonably good focus, then it will become pretty clear soon on that the 6d AF is its absolute weakest point. It is far outclassed by rebels from yester year- in both speed and accuracy.

Unfortunately for me, Ive has the 6d since late last year, and only recently have been able to get one lens focusing accurately. I invested in focal a ways back and its not helping my 24-1o5 + 6d combo at all. My 50 1.4 responded very well to focal adjustments. 70-200 II is good (not great) on the far end, still bad on the wide. With all of the af 'issues, i eventually plan on getting rid of it for a more reliable 5d3.

PS- 6d+50mm 1.4 combo (and a grip) is damn near a perfect camera setup, when it works well. even weight, light enough, etc...i love it.

 

[CarlTN]

CarlTN: I focus and recompose too. It's never been a problem, even with a 50L on a 6D. If I am getting paid for the shot then sure, I bag a few extra shots before I move on. The same goes if the subject is a person and he or she is not perfectly still, if its windy, or if I've had a couple of glasses of wine. As long as I am not careless I am fine. I always pixel peep, so as to learn from my mistakes. Focusing and recomposing is not the end of the world as some would have you believe. That being said, I do look forward to the day there is a camera that lets me place the focus point fast and effortlessly and that provides the same hit-ratio as focusing and recomposing + practice does. If you feel the need to use anything but the centre point, I do agree that the 6D AF is inadequate.

Well said, and I'm glad to see you weighing in on the focus recompose technique, especially considering you're using the 50L. But as I've said before, it's not so much that the outer points are useless in good light. It's that the processing that runs the autofocus system, will tend to deliberately not lock on anything if you leave all points active. It will bounce around all the points, and then arrive at a compromise of them all, which too often compromises the focus plane, and avoids the area with the strongest contrast (the area that a 5D3 or 1DX would have locked onto). Also, it gives too much weight to those outer points (again with all points active), and denies the better center point the precedence it should have. So, frankly I've had better success when relying on the outer points, if I just select one, rather than leaving all points active, especially in servo mode. That is just asking for trouble big time. I suppose it's easier for those with prejudice against the camera and its users, to just bash the camera and ignore people like me who point this out, though. To them, what is easiest and simplest, is best. But it's not accurate.

 

[CarlTN]

While it is true you are more limited with your AF points on the 6D, keep in mind you can focus and crop instead of recompose.

Certainly, but I'd consider it a a workaround in the extreme.

Well, considering that the 5D3 AF points definitely are far from filling the entire frame, it is a workaround you will have to employ on the 5D3 as well - perhaps just less frequently. At f/1.2, one should never focus and recompose even a smidgen as you well know due to the thin DOF.

More importantly, the 6D allows for easy switch to Eg-S focus screen unlike the 5D3 - so IMO 6D actually has a significant advantage for manually focusing the f/1.2 lenses and seeing their true DOF in the viewfinder.

Yes, the focusing screen can be installed (I have the Eg-S screen) but I'm specifically commenting on the AF which doesn't work too well with very large aperture lenses. Comparing the 5D3 AF with the 6D MF with Eg-S screen is like comparing apples to oranges. The 5D3 outer AF points will lock on with superb precision and you would have already taken the shot and moved on to another in the same time you would be focusing manually with the 6D.

Its not really comparing apples with oranges because the Eg-S allows you to see in the viewfinder more accurate DOF - even when autofocusing - than the 5D3's stock screen which is not user replaceable. 5D3's fixed focus screen only shows about f/2.8 DOF while the Eg-S on the 6D will come close to the DOF of f/1.2.

So, the fact that the 6D allows the user to swap to Eg-S means that what you see in the viewfinder when both AF *and* MF will more accurately represent the end product. If you do choose to MF to that end product, it is worlds easier on the 6D using Eg-S vs the 5D3's fixed screen.

Yes, the 5D3 will likely allow to set up your shots faster, but that does not make the 6D AF useless.

One could argue you are looking for trouble in general if you try to autofocus at f/1.2 all the time no matter what camera you use.

All EOS cameras AF with the lenses wide open, so a f/1.2 lens will AF wide open at f/1.2 no matter what settings you use to shoot.

Correct, when aperture is set to f/1.2 DOF is so thin that the very slightest difference between where you thought you were focusing and where the actual camera focused will cause loss of detail. MF with Eg-S/matte screen allows you to easily see if you got the shot or not before you take it - and you don't even have to go into Live View.

The cross type outer AF points work extremely well on the 5D3. See below photo taken with a 5D3 with 85L II - 100% crop of the AF area also provided - I have been using this combo for quite a while now and am happy with the results.

Not saying that 6D is a bad camera, but the whinging that takes place over the AF happens deservedly so.

Edit: I'm not sure how to post the 100% crop. The 100% crop image that I can view here on CR is larger than what I see in LR with a 1:1 view - any tips on how to post the exact image?

I think the whining about the 6D AF depends of what you take shots of. Birds, sure, the 6D AF probably not good for that. But for shooting people, the 6D AF is superb. Finally when one wants to MF (or see DOF when AF in viewfinder below f/2. 8), as one often may want to with an f/1.2 DOF, the 6D actually is better than the 5D3 IMO.

If the 5D3 had a user replaceable focus screen like the 6D (or a stock screen similar to the Eg-s) I'd be quicker to throw the 6D under the bus, but the 5D3 does not, which is certainly a large demerit against the 5D3 when AF or MF in the viewfinder with fast lenses at apertures wider than f/2. 8.

Very interesting and thoughtful observations, thanks very much. I am learning from you!

 

[CarlTN]

- The 6D's -3 EV lowlight sensitivity is currently unmatched by any DSLR on the market

If you shoot lowlight, sunsets, night photography or landscape photography the lowlight AF performance on the 6D wins.

As I pointed out a few pages ago in this thread:

How do you define 'low light'? For example, the difference between shooting at -2 EV and-3 EV could mean 1/15 s, f/2.8, ISO 51200 vs. 102400. Neither is very usable from an IQ standpoint. What most people call 'low light' is generally substantially brighter than either spec.

Long exposure night photograpy might benefit from that extra stop of AF capability (but in that situation, you are on a triod and probably using Live View to focus anyway). Sunsets, landscapes and general shooting have plenty of light relative to the AF sensitivity of even lower end dSLRs.

I think the -3 EV spec of the 6D is Canon saying 'we did it because we can, and to throw a bone after otherwise limiting AF functionality of this body' - it looks good on paper, but is of little practical benefit in the vast majority of shooting situations.

As I've said many times, due to the low noise of the 6D, the low light sensitivity of the center AF point, can be very useful in the majority of situations where you are shooting wildlife (or people) around, before, or after sunset. Or else if you are shooting landscape hand-held, with an IS lens, up to an hour after sunset...or during a full moon. Or if you are shooting inside a club, or outside on a dimly lit city street at night, that -3EV capability is very useful.

ISO 6400 is extremely usable for professional prints via the 6D (with a bit of post processing), and ISO's a bit above that are still useful.

As for bashing the other AF points on the 6D, you need to bash the 5D2's as well, because they were no better. It might not still be on sale, but plenty of forum readers still own and use the 5D2.

For anyone shooting with strobes, or shooting fast sports action in well lit areas, the 5D3 or 1DX is the camera you need (or perhaps a D800 at low ISO).

If you're shooting portraits with an f/1.4 lens, wide open at f/1.4, and require peripheral AF points to be used (for focusing on eyes, etc.), then yes the 6D will not give consistent results. But then the 1DX and 5D3 don't fare much better in that situation, which is why serious portrait photogs who shoot this way, either manually focus, or use live view. Of course most of them are closing that fast lens down quite a bit, in which case there is more wiggle room for AF inaccuracies.

And besides, in that peripheral area of these lenses (other than the Zeiss Otus)...those eyes that you claim are so razor sharp...actually are not, and are suffering from coma and astigmatism. It's unavoidable...especially with such lenses as the 50L and 85L.

This was fine until you mentioned the 5D3 not being much better than the 6D for f/1.4 portraits using the outer AF points. The 5D3 makes the 6D look broken doing this and it's a shame a 60D or a 7D would also make the 6D look broken.

+1 with RLPhoto, I have no problem with outer AF points on my 5D III. Doesn't matter 85L II or 50L

Photo below was taken with 5D III + 50L, outer AF point @ f1.2. Oops...sorry, that was f1.2 not f1.4 as he mentioned

That's a chair, not someone's eyes. Post one of those please.

A lot of thing to say...little to show :

1st photo SOOC, untouch: 5D III + 85L II, 1/160 @ f1.2, outer AF point, was focus on her left eye
2nd little edit in LR

BTW, I have no problem using AF in -3EV lighting condition, yes, with 5D III. Wanna see sample photos?

I thought you were discussing side AF points. Those eyes look pretty centered in the FOV to me, unless this is heavily cropped...which I doubt.

As I mentioned, 1st photo came straight out from camera, untouch, JPEG.

The only I did reduced photo size down to 3000x2000 for posting purpose(zero cropping). It was a 3rd outer AF point, from the center.

I'm not bashing 6D, but the #1 reason I went from 5D II to 5D III is 61 AF points. 5D II feel much better in hand...that just me of course.

That's fine for you, and that reasoning makes sense. If I needed 61 AF points, I would have bought something that had them. Again though, what I was referring to earlier, was the part of the image of an f/1.2 lens, that was outside the center 50% of the image. That is where the "sharpness" breaks down with such lenses, on a full frame camera, when set to full wide aperture...especially when you compare it to the center 50% of the image. Downsampling makes things look even sharper, but that is kind of the opposite of what I was speaking about. It's the conventional way of using such portrait lenses, because it works.

 

[CarlTN]

6D's AF capabilities and focus points are just plain sad for today's standards for a camera worth that much money and a FF label. Some people defend it by saying "it can take sports photos too!". Sure it can, I did it with my 550D also. I can make my eggs on a hot engine of my car, but I can do better.

Nobody denies 6D's low light focusing ability though.

6D low light focusing sensitivity -3Ev is not bad compared to -2Ev in 1DX and 5Dmk3 and I'm not happy with 5dmk3 ability to lock in low light.

Neither am I. That, and the lower cost, is what helped convince me I could use a 6D. I am happy with it. As I don't do wedding photography with flashguns or strobes, I don't need a 5D3. If I did professional sports, I would buy the 1DX without question. All of these cameras have their place in the line. Those that have not used a 6D for very long, who drone out their perpetual, boring, uninformative monotone about how it should not be produced or sold, are just plain wrong.

 

[mackguyver]

Neither am I. That, and the lower cost, is what helped convince me I could use a 6D. I am happy with it. As I don't do wedding photography with flashguns or strobes, I don't need a 5D3. If I did professional sports, I would buy the 1DX without question. All of these cameras have their place in the line. Those that have not used a 6D for very long, who drone out their perpetual, boring, uninformative monotone about how it should not be produced or sold, are just plain wrong.

The 5DIII is much better than the 5DII, but the 1D X seems much better than the 5DIII in low light. I don't know why anyone would say that about the 6D, it's an excellent camera and unless you shoot sports, wildlife, or other action, center point AF is really all you need, and by all accounts it's very good on the 6D. We got by for years with the 5DII's lousy AF, so anyone whining about the 6D needs to get a life.

 

[CarlTN]

Full size uncropped image. Autofocused with the 6D center point on the yellow bubble level, then recomposed. Apparently nobody else can do this, but my camera can while I'm bending over, and handholding it in a very dark room, at 1/13 second, f/1.8, 24mm, about 4 inches from the lens front element, with no image stabilization. It looked darker than this to my naked eye, and I don't think I used exposure compensation (the metadata doesn't show it if I did). Shot only as a jpeg, with some NR applied in LR. ISO 25,600.

What's all the fuss about focusing and recomposing? If little old me can do this, hand-held with no image stabilization, why can't others do it at 1/200 second in good light, or especially with strobes or flashguns? Not saying all lenses and focal lengths are the same...but gee whiz. It's not unheard of, because I did it.

The 'fuss' is that focus/recompose causes backfocus. It's simple geometry– the focal plane is flat (field curvature notwithstanding), and you're rotating the camera after locking focus, which moves the focal plane to a position behind the subject after recomposition. With a narrower aperture, the deeper DoF is often sufficient to mask the effect of the backfocus, but with a wide aperture, you'll see the backfocusing.

Frankly, your image of the ballhead is so dark and noisy that it's difficult to say anything is in sharp focus. But one thing that seems at least close to in-focus is the index mark on the left side of the clamp, and that's well behind the bubble level. That index mark is certainly more in focus than the lettering on the front of the clamp, despite that lettering being much closer to the bubble level. So if you did indeed successfully focus on the bubble level, then you've demonstrated (albeit poorly) the problem with focus/recompose.

It's not that 'nobody else can do this', but can ≠ should, and many of us know that focus/recompose causes problems with fast lenses shot wide open. If you're using a slower lens, stopping down your fast lens, or aren't a stickler for critical focus on your intended subject, focus/recompose can work.

You're conveniently ignoring the angle the shot was taken at. The plane of focus is on a double diagonal, relative to the plane the quick release plate exists in. Look at the area around the bubble level. What is immediately in front of it, is not in focus. What is immediately behind it, is not in focus. Sure there's noise, but I was making a point about the low light autofocus ability of the center point, to myself (I shot this in January). The 5D3 and 1DX, would not have autofocused at all in this light.

And of course the bubble level is not razor sharp. But consider the conditions. 1/13 of a second, at a distance of 4 inches, no image stabilization. The point is, the bubble level is in the plane of focus. You can try to deny it, but I'm sorry, it is.

Surely you're not saying the plane of focus at f/1.8 and 24mm, at a distance of only 4 inches, is more deep than the plane of focus of a 50mm f/1.2 lens, at a distance of 6 feet or greater (or whatever the average portrait distance might be the choice for such work with that lens)?

I'm not saying what you say is not correct, regarding the problems inherent with focus recompose technique. Also not saying it would automatically work as well with the 50L or 85L, with the 6D, because I have no experience with those yet, on it. However, other people who have posted recently, have related their efforts with the 50L on a 6D, and at least one has said they use "focus-recompose". If you have a problem with the technique, take it up with them. In any case, you have almost no experience with the 6D, thus your contributions to this thread are less valid, than those with more experience with the camera.

 

[CarlTN]

Neither am I. That, and the lower cost, is what helped convince me I could use a 6D. I am happy with it. As I don't do wedding photography with flashguns or strobes, I don't need a 5D3. If I did professional sports, I would buy the 1DX without question. All of these cameras have their place in the line. Those that have not used a 6D for very long, who drone out their perpetual, boring, uninformative monotone about how it should not be produced or sold, are just plain wrong.

The 5DIII is much better than the 5DII, but the 1D X seems much better than the 5DIII in low light. I don't know why anyone would say that about the 6D, it's an excellent camera and unless you shoot sports, wildlife, or other action, center point AF is really all you need, and by all accounts it's very good on the 6D. We got by for years with the 5DII's lousy AF, so anyone whining about the 6D needs to get a life.

+1 million!!! I completely agree! They need to get a life, and stop posting so much!

 

[3kramd5]

show proof that I am wrong, the AF measurement angle accuracy in Canons AF is F-2,8
I know Im right
it will be interesting!!!!

So you're suggesting that the sensor pair is too narrow to see beams from lenses wider than f/2.8? If that's the case, how do you believe any number of images online shot using canon AF at apertures in the f/<2.8 range were focused? Does the camera actually stop down to focus (as opposed to the normal practice of focusing wide open)?

 

[Loswr]

The 5DIII is much better than the 5DII, but the 1D X seems much better than the 5DIII in low light. I don't know why anyone would say that about the 6D, it's an excellent camera and unless you shoot sports, wildlife, or other action, center point AF is really all you need, and by all accounts it's very good on the 6D. We got by for years with the 5DII's lousy AF, so anyone whining about the 6D needs to get a life.

Exactly. Four years, many people (myself included) were clamoring for a camera that unified the image quality of the 5DII with the autofocus of the 7D. Canon delivered, even better than expected, with the 5DIII – and charged a premium for it. But they also delivered the 6D, basically a very modest update to the 5DII (already an excellent camera, AF notwithstanding) with a functionally equivalent AF system, but at a lower price. That's a win-win.

 

[Loswr]

To further add, my 1Ds3 and 1Dx never miss at f/1.4 on the outter points. Never. Always exact. No variability. Nails it everytime and that's even without AFMA.

it is physical impossibility because the AF measurement angle accuracy in Canons AF is F-2,8 ( eg.3,4)

That's not correct.

The specified precision is within the depth of focus at the max aperture of the lens for a standard precision AF point, and within 0.33 depth of focus (0.5 for some models) at the max aperture of the lens for a high precision AF point.

I discussed this issue with Chuck Westfall (Canon USA's technical mouthpiece), and this is part of his response:

"The fact that the AF points are functional with apertures as small as f/5.6, f/4 or f/2.8 respectively depending on the camera model and AF point under discussion does not imply that their measuring precision is limited to the depth of focus at those apertures. The AF detection system has the capability of calculating depth of focus based on the maximum aperture of the lens, whatever it happens to be."

show proof that I am wrong, the AF measurement angle accuracy in Canons AF is F-2,8
I know Im right
it will be interesting!!!!

Let's see… My evidence includes a statement from a technical advisor at Canon, giving information on the performance specification of a product made by Canon.

Your evidence is, "I know Im right."

The burden of proof is squarely on you. Frankly, I doubt it will be interesting, and if you are who I think you are, your past behavior has clearly shown your 'evidence' to be completely unreliable.