Canon 6D Dominates Low Light Focusing Test vs 5Dii, 5Diii & Nikon D600

[zim]

I think the thing that may have caused the confusion is that EV is often used interchangeably with "stops". There are countless cameras out there that adjust exposure compensation in EV values relative to the current setting, not the absolute standard EV value. I should have described it as relative stops instead, but though the results were still meaningful. I approached it from the perspective of an experienced wedding photographer who has been frustrated with the single point in low light.

As to your quandary about the 5Diii vs 6D, let me ask you this. What kind of shooting are you primarily going to do?

MM

Good question, a big old mixture is the answer I guess! over the years in no particular order architecture/family/aircraft/motor racing.
Next year unusually I have several events weddings/anniversaries/big holidays which are important to me and are without doubt a major driver to new kit. So stuff like the 5D3 flash AF assist issues and low light single point AF are important. That and I’m fed up camera sharing with my daughter. I have SD cards but the 5D3 doesn’t have fast SD, why Canon why!! I do like the faster fps but I want to be confident of focus in low light so lean towards 6D and the IQ looks a little better from what I’ve seen so far, but would the difference be seen on 20x16s I doubt it. I love prints, 20x16 max, If I get a few a year I consider worthy of my wall (yes wife has given me a wall in the house) I’m a happy bunny.
Overall I totally get what a well rounded camera the 5D3 is but boy are there things that just niggle. I love the thought of a camera that I really have to work at learning how to use I think the 5D3 AF system is a challenge, I want to have fun growing into it. I’m thinking of renting over Christmas but I really would prefer putting that money toward glass.

mmmm, you know I think this all boils down to for the most part that I’d be fine with either camera but which camera works best for those special events and that’s where I’m finding AF differences frustrating. The 5d3 should be a no brainer but it just isn’t…… aaarrrgggg

[jrista]

I don't have access to the standard...

In any case, it has no bearing on this discussion.

I do, but you're right.  However, we're talking about small (one stop or in most cases, much less) differences.  My point is that even though it's a relative measurement, labeling the test results as "-7 EV" is pretty darn misleading in light of the specified performance of the cameras being tested.  The difference between -2 EV and -7 EV is a 32-fold difference in light intensity.

It might be interesting to point out that as far as the AF sensor is concerned, the ISO setting does not matter a wit. For that matter, neither does the shutter speed. The only thing the AF sensor cares about is the actual amount of light allowed through the aperture. Shutter speed and ISO only factor in when the image is actually exposed on the image sensor...which is an entirely different aspect of the camera.

The term EV, or exposure value, is just a way to denote a quantity of light by describing it in terms of a given "exposure setting". You effectively have the same "EV" at 1s f/1 as you do at 2s f/1.4 or 16s f/4 or even 1/8s f/0.35! Those are all the same EV. It is usually initially derived at a standards-based ISO setting of 100...but the specific camera settings at which it is generally derived shouldn't change the actual meaning of EV 0, -2, or -3, nor mandate that the only valid way to achieve EV -3 is to use a 1s exposure at f/1 at an ISO of 100. It's just a scalar number that represents a known quantity, nothing else.

That said, I totally agree, indicating that the 6D can AF down to EV -7 is a rogue misrepresentation of both the 6D's capabilities, and a radical misunderstanding or misapplication of what an Exposure Value is. The 6D is clearly rated to AF down to EV -3...that would mean it could AF in as little light as that provided by a full moon (bit less than -2 EV from an illumination standpoint) with an f/1.2-1.4 aperture lens (knock off another 1 EV to reach -3, since we are letting in 1 stop less light than an f/1 lens).

[MichaelTheMaven]

Plenty of criticisms on semantics but why no alternative suggestions on methodology?

Lesson learned.

M

Ps- Jrista- I look forward to seeing your tests.

[neuroanatomist]

Plenty of criticisms on semantics but why no alternative suggestions on methodology?

Touched on that, as well...and you've got the perfect set of cameras for it!  Got any ND filters?  Set up a target lit at about 2 EV (lighting like you used for Target 2), then start knocking the light down with ND filters.  Alternatively, light a target with a dim desk lamp, then keep moving the lamp further away from the target.  The idea is to keep the same target, but decrease the light levels.  If possible, get them a stop or two lower than your Target 3, so you're below the rated spec of the 6D (and see how far you can push it...the 5DII seemed to go 1.5 stops lower than it's rated spec, and manage to AF, sort of).

[jrista]

Plenty of criticisms on semantics but why no alternative suggestions on methodology?

Lesson learned.

M

Ps- Jrista- I look forward to seeing your tests.

Heh, well, there are definitions and math, and there are ad-hoc tests. There is nothing wrong with an ad-hoc test, so long as it is represented accurately in the correct frame of reference. The definition of EV and the math adds up, and I believe your test is effectively falsified given the facts. We can derive the EV you were actually shooting at based on your exposure settings.

You stated that in your test "0" EV was 1/60s f/2.8 ISO 400. Well, first off, EV 0 cannot really be arbitrarily defined. Officially, EV 0 is "baselined" at 1s f/1. From an available-light standpoint, ISO does not actually matter. So, if EV 0 is officially 1s f/1, then a 1/60s f/2.8 exposure is actually EV 9 (6 stops difference in shutter speed, 3 stops difference in aperture). That is a difference of 12 stops total from an actual EF -3, and a total of 16 stops off from the EV -7 you claim in your test. This makes the assumption that at 1/60s f/2.8 ISO 400, your images were properly exposed (which, based on your blog, they were not...we'll get to that).

Since it is the AF sensor that really matters in the context of DSLR phase-detection AF, the shutter speed doesn't really actually matter either. In this context, the EV designation ultimately refers to a level of illumination on your AF target. If you really want to test AF at -3 EV, you should try it out under the light of a full moon on a clear night with an f/1.4 lens, such as the EF 50mm f/1.4. Assuming you were exposing correctly at 1/60s f/2.8, that would be like photographing a few minutes after sunset during "golden hour"...which is actually a LOT more light than photographing just by moonlight, even though it may appear to be rather dim to your eyes. According to your blog, you were testing indoors with standard house lighting. Indoor illumination is usually rated at around EV 7, however your target was directly in a spot of light illuminated by a very close light fixture that appeared to have multiple bulbs in it, so I'd say EV 9 sounds about right.

You were also underexposing by a significant degree. Again, it should be noted that as far as the AF sensor is concerned, the actual camera exposure settings do not matter, so trying to "simulate" EV -3 by underexposing a photo is not the same as autofucusing in EV -3 or even EV 0. You were actually autofocusing with quite a lot of light. The illumination from the area of your wall that you focused on was probably about EV 9, however you were using an f/2.8 lens rather than an f/1 lens (which, BTW, I am again assuming...Canon cameras always AF at maximum aperture...if your maximum aperture was wider than f/2.8, and you simply chose f/2.8 to force a certain underexposure, then my calculation here will be wrong.) At f/2.8, the AF sensor is effectively working at EV 6. That means that in your test case, instead running the 6D through it's paces at EV 0 (or for that matter EV -3 or -7), you were actually running it through its paces at EV 6.

I don't mean any offense, however your blog writeup about the 6D's AF performance will be eaten alive by anyone who understands how the AF system works, and understands the rough level of illumination of your AF target. The AF Unit, which resides underneath the mirror in the mirror box, contains a special light-splitting lens that directs light from both sides of the lens mounted to your camera onto various phase-detection strips in the AF sensor. The actual amount of light each strip has to work with is minuscule. If we were to describe it in terms of EV's, at EV -3 in your scene each strip is probably working at EV -5 or EV -6, it not less. The mirror will split the light from the camera lens in half, as 50% is reflected up through the viewfinder and the other 50% is redirected through the primary mirror to the secondary AF unit mirror underneath the primary. The AF Unit lens will further split that light for each AF strip. The central cross-type point in the 6D is composed of two diagonal strips, each of which would get around half of the 50% of light directed down to the AF Unit. That is at least two stops, assuming all of this mechanical redirection of light operates at 100% efficiency. Since nothing is perfectly efficient, the phase-detect strips on the AF sensor itself are really probably working at EV -6 to EV -7, when the illumination on your AF target is EV -3. None of this has anything to do with exposure settings...all that matters is the amount of light passing down the lens at maximum aperture. Since the EV scale is baselined at 1s f/1, if you use an f/1.4 lens, the AF sensor is working with even less light. If you use an f/2.8 lens (the minimum required for the central high-sensitivity AF point in the 6D to work), the AF sensor phase-detect strips are working at around EV -10, a vanishingly small volume of light!!! Hopefully this puts the incredible feat of phase-detection AF at EV -3 into, erm, proper light! (...yes, pun intended. ;P)

Now, I can't really say how much illumination the target on the floor under your desk may have had. It is quite possible you were getting closer to EV 0 at that point. However making a guess, even mildly educated as it may have been, is no substitute for using a proper light meter to actually measure the illumination under your desk in EV. It could very well have been that, as dark as it may have looked, the target under your desk was EV 2 or 3, if not higher. There is another caveat here as well. The kind of AF performance testing done by Canon is performed extremely carefully under very tightly controlled circumstances. The ambient temperature must be exact, the kind of lighting used to illuminate the test target must be full spectrum to introduce a proper and predictable amount of illumination, high frequency so as not to introduce a frequency oscillation that could interfere with the test (something that can occur with improperly designed ballasts for CFL bulbs that operate on a 60Hz power frequency), and test targets must be designed with the right level of contrast such that at the incredibly low levels of illumination below EV 0, the AF sensor can actually pick up differences in contrast at all.

I would not be surprised if the cameras failed or were slow to AF on the target under your desk due to a lack of contrast. Your carpet looks to be a dark gray or slightly off gray, with a black + as the target. In EV -3, I highly doubt anything would pick up enough contrast from that to really do anything. If you had stuck the target + on a piece of white paper, that would have created a slightly better test target for testing AF in low illumination, and even then, your at the boundary of the AF units rating, so AF will be spotty at best even in the most ideal of circumstances.

I hate to say it, but your test approach leaves a lot to be desired, and I believe many of the claims (such as EV -7) were fundamentally incorrect. It is highly ad-hoc, and makes use of a lot of guesswork. A lot of the critical factors, such as your definition of EV 0, or even the notion that camera settings have any impact on the AF system at all, are flat out incorrect. I think the only truly valid part of your test was the comparison of the central AF point with the outer AF points, and the conclusion that the central AF point being more sensitive was spot on, if already common knowledge.

As Neuro stated, you have the perfect set of cameras to perform such a test. Maybe, armed with more knowledge from my post here, and further armed with an actual incident light meter to get an accurate EV reading at your AF test targets, you can perform a more accurate and realistic test in a proper frame of reference.

[AudioGlenn]

man, u guys are too smart.  i just like to take pictures of things/people.  sometimes, when it's dark, I use a flash =)

[Ryan_W]

man, u guys are too smart.  i just like to take pictures of things/people.  sometimes, when it's dark, I use a flash =)

^ This.

Not that I don't appreciate the tests, because I do - and the responses too.  But this one is my favorite.  "things/people."

[skitron]

OK, got my 6D in and have done a bit of subjective testing. First off, IMO, the center point kicks butt and takes names in low light. With a 100L it locks focus in light low enough the IS doesn't seem to be able to work consistantly (if at all) and I can't see what it is I'm even focusing on (I'll let the peanut gallery determine what EV that is  ). The outer points need moderate light (as in a single lamp on in the room), but actually work pretty good on stuff that has some detail, but if it lacks detail, not so good (while the center would focus on the same thing).

Elsewhere I posted about how my 50D body had a substantial "bracket" in which it would confirm focus when manually focusing. It would confirm everything within the equivalent focus range of about 7 AFMA clicks. Meaning when focusing from infinity to closer in would back focus though confirming, while focusing from close to further out would front focus though confirming. And it would confirm anything in between. Meanwhile my 5D2 had a "bracket" of about 2-3 clicks. This 6D seems to be about like the 5D2, maybe a bit worse when manual focus, but autofocus from either direction seems pretty consistent so far with both a 100L and Sigma 50. Not perfect, but if AFMA is right it seems to be completely acceptable even at f1.4 and close up.

All in all, the experience is similar to the handling of a 60D body while getting 5D2 ISO and focus sytem on steroids. Meaning you get something way less than a 5D3 focus system (with the caveat the 6D center is somewhat better in low light), but IMO the 6D system is way better than the 5D2 because it works with so much less light (including the outer points compared to 5D2 outer points) plus seems substantially faster so far. And then there is the ISO, which is also pretty dang good. The video is pretty much the same as the 5D2, i.e. moire city, but certainly useable most of the time. So for me, a nice upgrade to 5D2 for stills, plus lighter and smaller to lug around. And a bit of an upgrade for video in that it will do all i-frame. Of course also not as durable, but seems beefy enough if you don't abuse it.

I did a cursory test of the center point in AI Servo by focusing on a business card about four feet away and then moving the camera towards the card at my best attempt at 1 ft per second and clicking while moving. It locked on with my 100L at 2.8, and that seems encouraging. That was with the default "AF ballistic" settings (which the 5D2 had none of).

Next I tried an outer point the same way. Epic fail. However, it did work when moving the camera about 1ft per second (maybe a bit less) at a distance of about 8 ft and f2.8. So somewhat encouraging that the outer points aren't basically useless like they were on 5D2. Subjectively, the outer points in this cursory test "feel" about like the center point on a 5D2 in AI Servo.

LOL, the real AI Servo test is the dreaded "kids on the swing set" tomorrow... I'll work both center and outers and post the results.

[edit] Just shot some 12800 night video...definite upgrade from 5D2...

[another edit] Another thing I noticed about this body is (1) I don't care for the button layout, and still won't even when I get used to it and (2) for me anyway, there is something about how it is balanced and holds in my hand and the way the shutter button feels that is resulting in way, way less camera shake. Again, that is just me and YMMV, but it is a very welcome thing. It holds true with all three of my lenses, which granted aren't all that different in terms of handling...

To sum it up, for me it was about $400 to do the upgrade from my 5D2 I bought a year ago, given what I sold it for, and so far feels like money very well spent.

[MichaelTheMaven]

Plenty of criticisms on semantics but why no alternative suggestions on methodology?

Touched on that, as well...and you've got the perfect set of cameras for it!  Got any ND filters?  Set up a target lit at about 2 EV (lighting like you used for Target 2), then start knocking the light down with ND filters.  Alternatively, light a target with a dim desk lamp, then keep moving the lamp further away from the target.  The idea is to keep the same target, but decrease the light levels.  If possible, get them a stop or two lower than your Target 3, so you're below the rated spec of the 6D (and see how far you can push it...the 5DII seemed to go 1.5 stops lower than it's rated spec, and manage to AF, sort of).

This is actually a pretty good suggestion. I have a couple sets of ND filters and light meter. Doable.

Having all 4 of these cameras is the hard part, putting together and redoing a new test would be simple. Please give me some more ideas and I can put them to another test.

Thanks

[neuroanatomist]

I don't mean any offense, however your blog writeup about the 6D's AF performance will be eaten alive by anyone who understands how the AF system works, and understands the rough level of illumination of your AF target.

^^ this

But, as stated, you've got the tools, and perhaps a better-designed test will provide more accurate answers.

I have a couple sets of ND filters and light meter. Doable.

"Where we did we put that light meter the albino had?"
"Over the albino, I think."
"Well, why didn't you list that among our assets in the first place?"

 

Keep jrista's points in mind, too - lens wide open, high contrast target (I mentioned that, before, as well).  You should have been using spot metering before (not sure if you were), but the light meter is definitely the best way to go.

[jrista]

"Where we did we put that light meter the albino had?"
"Over the albino, I think."
"Well, why didn't you list that among our assets in the first place?"

 

LOL!  Where in the world did THAT come from?!?

[DanielW]

I understand we're talking about focus speed and sensitivity of the central point, but has anyone tested the outer points with fast glass in terms of focus accuracy? Most of the tests I've found on the web, like Roger's, concern the central point exclusively.
I'm asking this because 11 AF points should be enough for me, if they're all really usable. Maybe the only situation for which I actually need the outer points is when shooting with a very shallow DoF and placing the focus zone very off-center, when composition would change too much and the focus-and-recompose technique would sure fail. (If the subject is not so close to the camera, then the angle changes little when recomposing and I can usually take a sharp pic, even with a shallow DoF.)
I sure appreciate -3 EV sensitivity, but in very low-light situations I won't be playing around with composition anyway, and having one reliable, sensitive central point sounds good enough, IMO. The precision of the outer points concerns me the most, for I can't rely very much on them when shooting with my 60D, even in reasonably well-lit situations.
(Sorry if it's been discussed before; I searched, but found nothing.)
Thanks!
Daniel

[RDPOE]

"Where we did we put that light meter the albino had?"
"Over the albino, I think."
"Well, why didn't you list that among our assets in the first place?"

 

LOL!  Where in the world did THAT come from?!?

A quote from "The Princess Bride" (altered to fit the situation, and much appreciated!!)

[pj1974]

"Where we did we put that light meter the albino had?"
"Over the albino, I think."
"Well, why didn't you list that among our assets in the first place?"

 

LOL!  Where in the world did THAT come from?!?

A quote from "The Princess Bride" (altered to fit the situation, and much appreciated!!)

Aha!! No wonder I love this forum... it was the Princess Bride connection all along!!   Love it.   

[jrista]

"Where we did we put that light meter the albino had?"
"Over the albino, I think."
"Well, why didn't you list that among our assets in the first place?"

 

LOL!  Where in the world did THAT come from?!?

A quote from "The Princess Bride" (altered to fit the situation, and much appreciated!!)

Aha!! No wonder I love this forum... it was the Princess Bride connection all along!!   Love it.   

Wow, that brings back memories. I haven't seen Princess Bride in such a long time, but oh, such fond, fond memories!