# 5D mark II versus 7D spot focus



## PeterJ (Sep 27, 2011)

I bought a 7D a while back over a 5D II and my main reasons at the time were the more advanced autofocus system plus higher fps. I'm an amateur but now I'm finding myself more confident I rarely take the camera out of manual, tend to meter based on a point of interest and for focus just about always use spot towards the center of the frame and recompose.

I've seen some complaints about the 5D autofocus but I'm guessing they are mainly about the lower number of focus points and less cross-type. Anyway I guess my question in general is from anyone that's used both would spot AF be noticeably different on either body? All my lenses are f/2.8 or faster, but sometimes I do take some photos in low-light conditions without AF assist where the 7D does hunt a while.


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## awinphoto (Sep 27, 2011)

In low light, the 5d Mark II will allow in more light to the focus sensor and will get quicker focus in those situations, however there are 5d Mark II owners that complain it STILL isn't fast enough, especially compared to some competition. The 7d will shine in better lit condition over the 5d mark II but it really is designed and geared for different audiences than the 5d mark II so take that for what it is. If you cannot use an AF lamp, could you use perhaps an external flash to get some help from the flash infrared lamp? Also if you couldn't use the larger spot focus or the spot plus 4 surrounding sensors? Relying on 1 focus mode in extreme situations can be tough but using larger or surrounding sensors (not to be confused with full zone focus or the 9 point focus modes). Lastly try using live mode with exposure compensation... assuming your exposure is set correctly, you should see the image decently on screen, set your focus point, you can either manual focus or use the live view focus, and shoot away...


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## [email protected] (Sep 27, 2011)

I too have used both most recently for video work and the rate of focus in good light between the 5DM2 and the 7D is VERY noticeable. I often use the Quick Focus setting to setup my video shot with live view on. Quick Focus is where it flips the mirror down, focuses and flips it back up to give you back live view. In Good light with the 7D this is a very quick process - It grabs the focus almost instantly and you are back to live view. On the 5DM2 it hunts, I found that I need to be more careful and give it a bit more of a contrasty spot to let it get focus. On both cameras I was using the same copy of the 24-70. In lower light it is a bit less noticeable but I VERY rarely feel like the 5DM2 grabs focus as quickly as the 7D.


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## Meh (Sep 27, 2011)

awinphoto said:


> In low light, the 5d Mark II will allow in more light to the focus sensor



What do you mean by this and why do you think that?


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## awinphoto (Sep 27, 2011)

Meh said:


> awinphoto said:
> 
> 
> > In low light, the 5d Mark II will allow in more light to the focus sensor
> ...



Almost every review comparison, by nature of a crop sensor collect x ammount of light and the full frame allowing in more ammount of light because of the bigger sensor, everything from the viewfinder will be slightly brighter, and more light will hit the autofocus sensor... In low light, by all means the 5d is not perfect and will also hunt, but can, in some instances, get focus a tad quicker than the 7D in extreme low light situations...


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## bchernicoff (Sep 27, 2011)

awinphoto said:


> Meh said:
> 
> 
> > awinphoto said:
> ...



The autofocus sensor is completely separate from the image sensor, so your answer makes no sense. 7D has more advanced AF across the board.


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## awinphoto (Sep 27, 2011)

If i may, the autofocus sensor receives light from the mirror so the more light hitting the mirror, the more light gets sent to the autofocus sensor... they are 2 separate sensors... the 7d DOES have a more advanced sensor, but light being light, if it doesn't receive as much light as the 5d does, it can only do so much... In good lighting, the 7D kicks the 5d's butt every which way, but in low light, lighting becomes even more important. 

If you will, here's what I mean... the crop sensor is 1.6 smaller than a full frame sensor... a little more than half the size than a full frame sensor... Take 2 softboxes... both pumping out the same quality and strength of light... If 1 is on and the other is off, that's basically what a crop sensor is getting in light... a full frame camera would be like turning on the second softbox of light... you're not increasing any intensity of light but it's a bigger source overall 1 vs 2 and so it's more light and in terms of exposure, that's around 1 stop difference. The full frame mirror will receive 2x the light gathered from the lens (all the light the lens can send it) and that light bounces into the AF motor. The crop sensor still gets all that light but the mirror is smaller, sensor is smaller, and a lot of light is then wasted and not used...


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## bchernicoff (Sep 27, 2011)

PeterJ said:


> I bought a 7D a while back over a 5D II and my main reasons at the time were the more advanced autofocus system plus higher fps. I'm an amateur but now I'm finding myself more confident I rarely take the camera out of manual, tend to meter based on a point of interest and for focus just about always use spot towards the center of the frame and recompose.
> 
> I've seen some complaints about the 5D autofocus but I'm guessing they are mainly about the lower number of focus points and less cross-type. Anyway I guess my question in general is from anyone that's used both would spot AF be noticeably different on either body? All my lenses are f/2.8 or faster, but sometimes I do take some photos in low-light conditions without AF assist where the 7D does hunt a while.



I own both and here is the breakdown. The 7D's autofocus is much more advanced. Does this matter for portraits and landscapes (non-moving subjects)...probably not very much. With both bodies, I have set them so AF doesn't engage with a shutter press, but with the AF On button. On the 5D, I almost always have set to the center point only, and press the AF On button 2 or 3 times when shooting in a situation that makes good AF difficult. For my taste the center point is too large, which brings me to the one real advantage of the 7D when talking about non-moving subjects...enabling the smaller, precise center point that is disabled by default. It offers a true pinpoint for focusing on small subjects that may be behind something larger (squirrel face looking out from behind a fork in a tree branch). In this case, the 5D or the default center point on the 7D will want to focus on the foreground object.

When it comes to sports or moving subjects, setting the 7D to use the 9 center points and AI-Servo, will blow away the 5D on AI-Servo. The 5D is still not bad in this area, but it is much harder to keep the focus on the moving subject...you really have to concentrate. For sports, you should definitely set the AF to start with shutter press.

The Too Long Didn't Read of all this is: 7D has better AF than 5D Mk II, but the 5D Mk II's AF is plenty good. For me, the image quality of 5D is more important than the slightly better AF of the 7D. UNLESS, I am shooting sports, then I grab my 7D every single time and set it to 8fps, 9 center AF points, and AI_Servo.


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## bchernicoff (Sep 27, 2011)

awinphoto said:


> If i may, the autofocus sensor receives light from the mirror so the more light hitting the mirror, the more light gets sent to the autofocus sensor... they are 2 separate sensors... the 7d DOES have a more advanced sensor, but light being light, if it doesn't receive as much light as the 5d does, it can only do so much... In good lighting, the 7D kicks the 5d's butt every which way, but in low light, lighting becomes even more important.
> 
> If you will, here's what I mean... the crop sensor is 1.6 smaller than a full frame sensor... a little more than half the size than a full frame sensor... Take 2 softboxes... both pumping out the same quality and strength of light... If 1 is on and the other is off, that's basically what a crop sensor is getting in light... a full frame camera would be like turning on the second softbox of light... you're not increasing any intensity of light but it's a bigger source overall 1 vs 2 and so it's more light and in terms of exposure, that's around 1 stop difference. The full frame mirror will receive 2x the light gathered from the lens (all the light the lens can send it) and that light bounces into the AF motor. The crop sensor still gets all that light but the mirror is smaller, sensor is smaller, and a lot of light is then wasted and not used...



You have to remember that each AF point only sees a very small amount of the total reflected light. The smaller mirror means that less total light is reflected, but this in no way diminishes the intensity of each point of light reflected up to each AF point. Using your 2x figure, the full-frame mirror reflects 2 times as many points of light as the crop mirror, but each of those points of light are the same intensity. If the AF points on the sensor are the same size between the bodies, each AF point receives the same amount of light. I do not know if they are the same size and if you have experimentally determined that in identically conditions with the only variable being the body, that the 5D has better AF performance, than this argues that each AF point is larger or more sensitive.


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## awinphoto (Sep 27, 2011)

bchernicoff said:


> awinphoto said:
> 
> 
> > If i may, the autofocus sensor receives light from the mirror so the more light hitting the mirror, the more light gets sent to the autofocus sensor... they are 2 separate sensors... the 7d DOES have a more advanced sensor, but light being light, if it doesn't receive as much light as the 5d does, it can only do so much... In good lighting, the 7D kicks the 5d's butt every which way, but in low light, lighting becomes even more important.
> ...



Not if you think about terms of exposure... 2x the light means 1 stop difference... 1 stop difference means more overall intensity of light overall... The light source intensity hasn't increased but adding that extra bit of light makes a world of difference on exposure and in this example, light hitting each AF point.


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## K-amps (Sep 27, 2011)

awinphoto said:


> If i may, the autofocus sensor receives light from the mirror so the more light hitting the mirror, the more light gets sent to the autofocus sensor... they are 2 separate sensors... the 7d DOES have a more advanced sensor, but light being light, if it doesn't receive as much light as the 5d does, it can only do so much... In good lighting, the 7D kicks the 5d's butt every which way, but in low light, lighting becomes even more important.
> 
> If you will, here's what I mean... the crop sensor is 1.6 smaller than a full frame sensor... a little more than half the size than a full frame sensor... Take 2 softboxes... both pumping out the same quality and strength of light... If 1 is on and the other is off, that's basically what a crop sensor is getting in light... a full frame camera would be like turning on the second softbox of light... you're not increasing any intensity of light but it's a bigger source overall 1 vs 2 and so it's more light and in terms of exposure, that's around 1 stop difference. The full frame mirror will receive 2x the light gathered from the lens (all the light the lens can send it) and that light bounces into the AF motor. The crop sensor still gets all that light but the mirror is smaller, sensor is smaller, and a lot of light is then wasted and not used...



The image sensor as you say is not the same as the focus sensor... are you saying the 7D has a crop (1.6x) *focus * sensor too?? :-\


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## awinphoto (Sep 27, 2011)

K-amps said:


> awinphoto said:
> 
> 
> > If i may, the autofocus sensor receives light from the mirror so the more light hitting the mirror, the more light gets sent to the autofocus sensor... they are 2 separate sensors... the 7d DOES have a more advanced sensor, but light being light, if it doesn't receive as much light as the 5d does, it can only do so much... In good lighting, the 7D kicks the 5d's butt every which way, but in low light, lighting becomes even more important.
> ...



The focus sensor isn't smaller but the light allowed through to the mirror to the AF sensor is proportional by the diminished light.... Canon isn't going to waste money putting a full frame size mirror into a crop body when it doesn't need it. Plus by doing so, you would see image you wouldn't be getting anyways... When you read reviews about the 5D's viewfinder, you read adjectives such as Big, bright, pictureframe... when you do the math, it makes perfect sense...


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## awinphoto (Sep 27, 2011)

Dont get me wrong, I have the 7D and shoot regularly with 7D... I shoot almost 90% of my shots with that great camera... but it does have it's limitations and when the new 5d's are released... can you imagine what the 7D AF with the more light input of the 5D can pump out? When that camera comes, if it has the same AF as the 7D, i'm dumping my 7D's in favor of the 5d's...


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## sb (Sep 27, 2011)

PeterJ, I have both cameras. It is my subjective opinion that 5D does better in low light/contrast situations, but there is no question that 7D's system is noticeably better overall. That being said, Mk2's system is as good as I ever need it to be for what I do. If I were shooting sports, I'd definitely favor the 7D, hands down.

Simply put - these 2 cameras complement each other. One has better IQ (Mk2), one is faster (7D) so it boils down to what you shoot.


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## Mt Spokane Photography (Sep 27, 2011)

I have both as well as having had a 1D MK III for the last two years. For focus accuracy and low light focus, my 5D MK II beats the others. For tracking moving objects, the 7d and 1D MK III are much better.

Speed of AF is largely a function of the lens used, but my 1D MK III was noticibly faster to AF, and in some cases, so is the 7d.

If you are one of those trying to focus on very fast moving objects or track them as they move from side to side, the 7D and 1D MK III will obviously be better.

If you have a wide aperture lens like a 35mmL, the 5D MK II will focus more accurately (using the center point), and the larger viewfinder of the 5D MK II and 1D MK III makes manual focusing much easier.


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## bchernicoff (Sep 27, 2011)

awinphoto said:


> The focus sensor isn't smaller but the light allowed through to the mirror to the AF sensor is proportional by the diminished light.... Canon isn't going to waste money putting a full frame size mirror into a crop body when it doesn't need it. Plus by doing so, you would see image you wouldn't be getting anyways... When you read reviews about the 5D's viewfinder, you read adjectives such as Big, bright, pictureframe... when you do the math, it makes perfect sense...



You are missing the point completely and I won't argue it further than this: When I bounce a laser pointer off a mirror onto a wall, the brightness of the laser dot on the wall doesn't change depending on the size of the mirror I bounce it off of.


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## candyman (Sep 27, 2011)

bchernicoff said:


> ................................
> When it comes to sports or moving subjects, setting the 7D to use the 9 center points and AI-Servo, will blow away the 5D on AI-Servo. The 5D is still not bad in this area, but it is much harder to keep the focus on the moving subject...you really have to concentrate. For sports, you should definitely set the AF to start with shutter press.
> ....................................



When you say: "....AF to start with shutter press" Do you mean : C.FnIII:Autofocus/Drive - AI Servo 1st/2nd image priority [2] set to *option 3*?

And, I try to understand the "9 center points".....
I have set mine to: C.FnIII:Autofocus/Drive - Select Af Area selec. mode [6] set to Man. Selec.: AF point expansion

Further: 
C.FnIII:Autofocus/Drive - AI Servo Tracking Method [3] set to* option 1* (Continuous AF track priority)

C.FnIII:Autofocus/Drive - AI Servo tracking sensitivity [1] set to 1 left from the middle towards slow


I am trying to verify some settings here because since 3 weekends I am trying different settings while taking photos at the soccergames of my son. I didn't yet find the right / optimal setting for my Canon 7D


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## awinphoto (Sep 27, 2011)

bchernicoff said:


> awinphoto said:
> 
> 
> > The focus sensor isn't smaller but the light allowed through to the mirror to the AF sensor is proportional by the diminished light.... Canon isn't going to waste money putting a full frame size mirror into a crop body when it doesn't need it. Plus by doing so, you would see image you wouldn't be getting anyways... When you read reviews about the 5D's viewfinder, you read adjectives such as Big, bright, pictureframe... when you do the math, it makes perfect sense...
> ...



And I wont argue this matter any futher. any single point in a F5.6 exposure (with the same shutter) would be letting in 2x the light in every part of the frame than a F8 exposure... Same with the mirror.


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## Meh (Sep 27, 2011)

Many correct and incorrect points in all of the above. And personal experience is what it is, so it could be that the 5D2 does have better at AF in low light situations but perhaps not for the reasons being stated. Like everything else, there are tradeoffs in designing sensors and the 5D2 might have a larger AF sensor pixels which would have certain trade offs and could be helpful in low light at the expense of precision of the AF system but I'm not sure what those design choices or optimal design is.

Brightness is light per unit area. If you focus the scene down to a smaller size the light per unit area increases and the image appears brighter. The 5D2 view finder is a 0.76 magnification while the 7D is 1.0 and this is why the 5D2 viewfinder appears brighter. It is not because more total light is being collected; that is true but you are also observing a larger angle of view so the light per unit area remains constant. The brightness of the scene does not increase because you are looking at a bigger scene.

However, this has nothing to do with the AF sensors. Each AF sensors is only looking at a small area in a few points of the image (9 for 5D2, 19 for 7d, 45 for 1D4). In other words, it's a small bundle of rays NOT all the rays concentrated to a spot. It is irrelevant that the image size, field of view, sensor size, or mirror size is different for each camera or that different total amounts of light are collected.

The analogy given about the laser reflecting off the mirror correct... the bundle of rays reflecting off the mirror is the same whether the mirror is the size of dime, a quarter, or a football field.


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## Meh (Sep 27, 2011)

awinphoto said:


> And I wont argue this matter any futher. any single point in a F5.6 exposure (with the same shutter) would be letting in 2x the light in every part of the frame than a F8 exposure... Same with the mirror.



Regarding the aperture, that is a true statement. But it is not the same with the mirror. The points of light coming through the lens for a given aperture setting will not be further affected by the size of the mirror.


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## awinphoto (Sep 27, 2011)

I'm all for the discovery of the truth, so lets drop the intensity of light debate (even though, all things being equal, the bigger mirror, the more light, even if the center portion that would be collected by a crop sensor may or may not be equal intensities, the extra surrounding information may or may not be enough to affect exposure and light), but lets assume that's all equal... Let's take a 40D and a 5D mark 2 (same AF system)... Assuming the AF points are pretty much in equal or equal like proportion to the frame on the 40D and 5d mark II or at least the individual AF sensor size within the frame, and since the 5D is 1.6x bigger, then that would possibly mean, at least to the layman, that assuming the AF sensor isn't necessarily bigger, but if there were lets say 20 pixels of information per each sensor size on a crop sensor, on a full frame, there would be 36 pixels, hence more information going to the sensor, which allows it to be better in low light, which is the original problem that was in question. Any debates about this thinking?


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## neuroanatomist (Sep 27, 2011)

awinphoto said:


> The focus sensor isn't smaller but the light allowed through to the mirror to the AF sensor is proportional by the diminished light.... Canon isn't going to waste money putting a full frame size mirror into a crop body when it doesn't need it. Plus by doing so, you would see image you wouldn't be getting anyways... When you read reviews about the 5D's viewfinder, you read adjectives such as Big, bright, pictureframe... when you do the math, it makes perfect sense...



Sorry, but that's just not correct. Yes, the reflex mirror is larger in FF camera than in an APS-C camera, which menas a bigger, brighter viewfinder, but that's completely irrelevant for the AF system. First off, the reflex mirror reflects most of the light up to the viewfinder, and allows a small amount of light to pass straight through the mirror to be reflected downward by the secondary mirror. Importantly, the secondary mirror is much smaller than the main mirror, and only a small portion in the center of the main mirror is semitransparent, to allow light through for the AF system. 

The key point is that for a lens with a given max aperture, the light per unit area is the same, regardless of image sensor size. The light hitting any one point on the sensor (image sensor or AF sensor) is the same. The FF sensor gathers more light because the total area of the sensor is larger, and likewise the VF is brighter because the total area of the VF is bigger. I don't know the exact measurements in real units for the dimensions of a single AF point, but for the 5DII's AF points to receive more light, the individual points would need to be larger than their 7D counterparts. I can almost guarantee that's not the case for the center AF point, since the f/2.8-sensitive 'X'-shaped (diagonal) cross sensor on the 7D sits outside the standard '+' shaped f/5.6-sensitive center AF point, meaning it is almost certainly physically larger than the 5DII's center AF point, and with a larger area and the same light per unit area, that the 7D's center AF point is getting more light than the 5DII's center AF point.



bchernicoff said:


> When I bounce a laser pointer off a mirror onto a wall, the brightness of the laser dot on the wall doesn't change depending on the size of the mirror I bounce it off of.



Exactly - light per unit area is the same.



awinphoto said:


> And I wont argue this matter any futher. any single point in a F5.6 exposure (with the same shutter) would be letting in 2x the light in every part of the frame than a F8 exposure... Same with the mirror.



Well, I'll argue further.  The above statement is correct, but irrelevant. An f/5.6 exposure lets in 2x the total light than f/8 over the entire image circle, true. But that's true whether there's a FF sensor sitting in that image circle, or an APS-C sensor sitting in that image circle, or the even smaller AF sensor sitting in that image circle. The smaller the sensor, the less of that image circle is sampled by the sensor. Same light coming through the lens, less light detected by a smaller sensor. 

You seem to be implying that the sensor size affects exposure - it does not. If you meter a scene with a given aperture, you should get the same shutter speed for both APS-C and FF (and for MF and a tiny digicam, too). Sensor size does not affect exposure, because exposure is determined by the light per unit area, which is determined by the f/number and independent of sensor size. 

Hopefully, the above clearly demonstrates that the amount of light hitting both the 5DII and 7D AF points is the same. Fine, but that's not the only factor. Different AF sensors and different points within those sensors can have different absolute sensitivities. Even two AF points with the same rated sensitivity (e.g. f/5.6-sensitive horizontal lines) can have different absolute sensitivities in terms of the amount of light required to achieve a focus lock. So, even if the same amount of light is hitting the AF point, one AF point may simply be more sensitive (e.g. applies a higher internal gain while maintaining adequate S/N to achieve a lock, much in the same way that newer image sensors can achieve higher ISO values with equivalent noise). 



But enough theory. How about the real world?

Overall, when comparing the 5DII AF with the 7D AF, I would rank them as follows: 5DII center AF point > 7D center AF point > 7D off-center AF points >> 5DII off-center AF points. More specifically, the 5DII's center AF point outperfoms the 7D's AF points slightly in terms of accuracy and noticeably in terms low-light sensitivity. The 7D's center AF point is quite good, and the off-center AF points of the 7D are nearly as good as the center AF point. Comparitively, the off-center AF points of the 5DII suck, and I only use them in bright light, preferably with contrasty subjects. For AI Servo tracking, the 7D wins, hands-down.



PeterJ said:


> ...for focus just about always use spot towards the center of the frame and recompose.



That is fine sometimes, but if you start using fast lenses (f/2 and faster) shot wide open, that technique can lead to your subject being out of focus. See this linked article for more details on the problem with focus-recompose. 



PeterJ said:


> Anyway I guess my question in general is from anyone that's used both would spot AF be noticeably different on either body?



I don't think anyone has specifically addressed this issue. If by 'spot AF' you mean that mode on the 7D, there is no such mode on the 5DII. With Spot AF, the AF system reduces the effective size of the AF points. Most people aren't aware that the actual AF point is significantly larger than the little box that represents the AF point in the viewfinder. That's one thing that leads to complaints about AF - you place the box right on the small feature you want to focus on, but the actual AF point is larger, and if there's a high-contrast feature that's just outside of your selected AF point 'box' the camera will lock onto that instead of what you put the box over. The 7D's Spot AF restricts the region of the AF point used to an area approximately equal to the size of the box in the viewfinder (note: not the tiny inner box that indicates Spot AF, but rather the larger, main AF point box). 



PeterJ said:


> All my lenses are f/2.8 or faster, but sometimes I do take some photos in low-light conditions without AF assist where the 7D does hunt a while.



Back to my statement above. The center AF point of the 5DII does better in low light than the center AF point of the 7D. With the center point, my 5DII will get an AF lock in lighting conditions so dim that the 7D would hunt and give up. With a Speedlite mounted, the AF assist comes on sooner and more often with the 7D than with the 5DII.

I presume you avoid the AF assist on the 7D because the strobing of the popup flash is annoying - I know that's the case for me. You might consider using a Speedlite - you can set it so the flash doesn't fire, only the AF assist lamp does, and the AF assist is a much less offensive red grid (just be sure to get one with the dedicated lamp, like the 430EX II - lower flashes, e.g. 270EX II, just strobe the main tube like your popup flash).

Hope that helps...


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## Meh (Sep 27, 2011)

awinphoto said:


> I'm all for the discovery of the truth, so lets drop the intensity of light debate (even though, all things being equal, the bigger mirror, the more light, even if the center portion that would be collected by a crop sensor may or may not be equal intensities, the extra surrounding information may or may not be enough to affect exposure and light), but lets assume that's all equal... Let's take a 40D and a 5D mark 2 (same AF system)... Assuming the AF points are pretty much in equal or equal like proportion to the frame on the 40D and 5d mark II or at least the individual AF sensor size within the frame, and since the 5D is 1.6x bigger, then that would possibly mean, at least to the layman, that assuming the AF sensor isn't necessarily bigger, but if there were lets say 20 pixels of information per each sensor size on a crop sensor, on a full frame, there would be 36 pixels, hence more information going to the sensor, which allows it to be better in low light, which is the original problem that was in question. Any debates about this thinking?



Yes. First, let's just clarify the difference in sensor size so there's no confusion for others. 1.6x refers to the diagonal measurement. The FF sensor is actually 2.5 times larger in area than the APS-C sensor.

You may realize this but it's not clear from your statements and others may not know. The AF sensor is completely separate from the image sensor (it's usually at the bottom of DSLR camera bodies) so therefore the relative size, resolution, pixel pitch, etc. between image sensors in various cameras has nothing to do with the AF sensors in all those cameras. The AF sensors do not need to scale (in terms of size or pixel size) along with the image sensors.

I'm not really sure exactly what you mean by "more information going to the sensor" but that's not really how phase detect AF works.


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## awinphoto (Sep 27, 2011)

Meh said:


> awinphoto said:
> 
> 
> > I'm all for the discovery of the truth, so lets drop the intensity of light debate (even though, all things being equal, the bigger mirror, the more light, even if the center portion that would be collected by a crop sensor may or may not be equal intensities, the extra surrounding information may or may not be enough to affect exposure and light), but lets assume that's all equal... Let's take a 40D and a 5D mark 2 (same AF system)... Assuming the AF points are pretty much in equal or equal like proportion to the frame on the 40D and 5d mark II or at least the individual AF sensor size within the frame, and since the 5D is 1.6x bigger, then that would possibly mean, at least to the layman, that assuming the AF sensor isn't necessarily bigger, but if there were lets say 20 pixels of information per each sensor size on a crop sensor, on a full frame, there would be 36 pixels, hence more information going to the sensor, which allows it to be better in low light, which is the original problem that was in question. Any debates about this thinking?
> ...



I should have used some other form of measurement, but I was referring to size of each AF sensor compared from a crop camera to a full frame So in relation IF a sensor in a crop camera covered an area compard to the same sensor in a full frame, all things being equal, would be covering 1.6x more information


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## bchernicoff (Sep 27, 2011)

candyman said:


> When you say: "....AF to start with shutter press" Do you mean : C.FnIII:Autofocus/Drive - AI Servo 1st/2nd image priority [2] set to *option 3*?



I am at work and don't have my camera handy, so I probably used some incorrect terms. I pulled up the owners manual and was referring to C.Fn IV -1 (pg 217 - 219 in the English owners manual). I have the shutter button set to "Metering Start" and the AF On button set to "Metering and AF Start". This means that half-pressing the shutter does not autofocus it only meters. You must now press AF On button to start focusing. Think of it as having the camera set to manual focus in terms of being able to focus separately from metering or taking the picture, but still getting the benefit of AF, when you press the AF On button. Again, I don't recommend this for moving subjects. For sports, I recommend what I said below:



candyman said:


> And, I try to understand the "9 center points".....
> I have set mine to: C.FnIII:Autofocus/Drive - Select Af Area selec. mode [6] set to Man. Selec.: AF point expansion



I was referring to Zone AF, with the central zone (9 points) selected, page 90 in the English owners manual. This really helps with AI-Servo tracking for me. I also have set my AI Servo tracking sensitivity to the most sensitive as I am usually shooting motorcycles which are quite fast moving.


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## Meh (Sep 27, 2011)

awinphoto said:


> Meh said:
> 
> 
> > awinphoto said:
> ...



By "more information" I assume you mean more pixels over a larger area for each AF point but that would not improve the AF. 

In simplified terms, phase detect AF is just looking for a peak along the strip of pixels that make up the sensor. It then compares that to the peak along the other strip of pixels (each AF point is actually two sensors) and looks to see if they "match", if not the AF system tells the lens to adjust to the correct focus position (phase detect AF determines this precisely, contrast AF does not which is why it is slower and cannot track focus).

There is no need to have more pixels covering a larger area because the peaks don't move very far between focused and unfocused.


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## neuroanatomist (Sep 27, 2011)

awinphoto said:


> ...I was referring to size of each AF sensor compared from a crop camera to a full frame So in relation IF a sensor in a crop camera covered an area compard to the same sensor in a full frame, all things being equal, would be covering 1.6x more information



Actually, in _relative_ terms the AF sensor on the 5DII is smaller than the sensor on the 7D, i.e. the spread of the AF points on the 7D covers a larger proportion of the image frame compared to the 5DII. That's one complaint about the 5DII's AF system - there are no AF points anywhere near the 'rule-of-thirds' intersections, whereas there are on the 7D, and on FF bodies like the 1DsIII (sidebar: I love Canon's somewhat deceptive advertising on the 5DII's AF, where they state in the white paper that 9 AF points in the 5DII have the same horizontal spread as the 45 points in the 1DsIII - that's true, but the much-reduced vertical spread means the diagonal points don't reach the thirds intersections). 

Ok, so the relative size is slightly larger on the 7D is slightly larger than the 5DII, but the absolute size of the 5DII's Af sensor is larger, so the 5DII's AF sensor gets more total light than the 7D's AF sensor. That's totally irrelevant. Unlike an image sensor, the AF sensor is not a full CMOS or CCD sensor that gathers light over it's entire area. The light is gathered by a small number of discrete regions - the AF points. Each AF point operates independently of the others, they don't 'add up' the light. So, unless there are data to support the idea that the individual AF points are substantially larger or smaller from one model to the next, there is no sensitivity difference based on the amount of light reaching the AF sensor (but, as stated above, _electronic_ differences between sensors can result in different sensitivities).


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## KyleSTL (Sep 27, 2011)

awinphoto,

For a given aperture (regardless of focal length, since aperture is a ratio of focal length and iris diameter) the light *PER UNIT AREA* is identical regardless of format (1/1.7", APS-C, 35mm, medium format, etc). Your statement of the 5D Mark II's AF sensor receiving more light is only true if (and only if) the individual focus points are larger than the 7D's focus points. The overall amount of light reflected by the mirror (which is dependent on mirror size, and therefore sensor size) is completely irrelevent to the light used for any given AF point.

The relevent question is (all other things being equal):

How big are individual AF points of the 5D Mark II vs. the 7D?


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## TexPhoto (Sep 27, 2011)

Have both. 7D AF is better and faster. It's a sports oriented camera to me anyway. 

And as other's have stated, crop factor has nothing to do with AF sensor size/sensitivity. I don't know if the actual sensors in the camera are bigger smaller, etc. but the size of the sensor would not effect the AF system.


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## neuroanatomist (Sep 27, 2011)

TexPhoto said:


> Have both. 7D AF is better and faster. It's a sports oriented camera to me anyway.



Agreed that the 7D is better, mostly. In good light, and for moving subjects, the 7D wins. Personally, I find that the center AF point of the 5DII is better in very low light. But that's probably appropriate - in light dim enough to give the 7D AF system problems, the ISO for the shot would probably be higher than I comfortably go on the 7D (unless I have a Speedlite attached, in which case, the AF assist lamp obviates the low-light AF problems).

Do you find that the 7D autofocuses well in low light without an AF assist?

One other observation - with some lenses, the 5DII seems achieve an AF lock faster, even in good light. When doing AF microadjustments (where I take several shots starting from MFD and several from infinity to a target at a fixed distance), I notice that with some lenses (e.g. 85mm f/1.2L II, 100mm f/2.8L Macro IS) the 7D tends to slightly overshoot, then go back to the correct focus, whereas the 5DII just seems to move to the correct focus and stop. It might be happening with all lenses - the two above have overall slower AF than lenses like the 70-200mm f/2.8L IS II or the 135mm f/2L, so I may just be missing that occurrence with the faster-focusing lenses. 



KyleSTL said:


> How big are individual AF points of the 5D Mark II vs. the 7D?



To refine that a bit further, even an 'AF point' isn't a single sensor unit - each AF point is composed of multiple, discrete sensors. Here's what the center AF point of the 7D looks like (along with the smaller points to the right and left):







The light-sensitive area of the AF point is only a tiny fraction of the area we're calling an 'AF point'.


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## PeterJ (Sep 27, 2011)

Thanks everyone for the feedback .



neuroanatomist said:


> I don't think anyone has specifically addressed this issue. If by 'spot AF' you mean that mode on the 7D, there is no such mode on the 5DII. With Spot AF, the AF system reduces the effective size of the AF points. Most people aren't aware that the actual AF point is significantly larger than the little box that represents the AF point in the viewfinder. That's one thing that leads to complaints about AF - you place the box right on the small feature you want to focus on, but the actual AF point is larger, and if there's a high-contrast feature that's just outside of your selected AF point 'box' the camera will lock onto that instead of what you put the box over. The 7D's Spot AF restricts the region of the AF point used to an area approximately equal to the size of the box in the viewfinder (note: not the tiny inner box that indicates Spot AF, but rather the larger, main AF point box).


That I didn't realise and probably isn't something I'd enjoy, as the article you linked mentioned focus and recompose does have some things to be wary of but I've always preferred the 7D spot mode over single-point. Having said that I'm sure it's something I'd get used to and just a matter of knowing the limitations.



neuroanatomist said:


> Back to my statement above. The center AF point of the 5DII does better in low light than the center AF point of the 7D. With the center point, my 5DII will get an AF lock in lighting conditions so dim that the 7D would hunt and give up. With a Speedlite mounted, the AF assist comes on sooner and more often with the 7D than with the 5DII.
> 
> I presume you avoid the AF assist on the 7D because the strobing of the popup flash is annoying - I know that's the case for me. You might consider using a Speedlite - you can set it so the flash doesn't fire, only the AF assist lamp does, and the AF assist is a much less offensive red grid (just be sure to get one with the dedicated lamp, like the 430EX II - lower flashes, e.g. 270EX II, just strobe the main tube like your popup flash).
> 
> Hope that helps...


I agree the popup is vastly annoying. I've got a 580EX II and do find the AF assist beam is good, but for some shots prefer them to be candid rather than that "oh look we're about to have out photo taken" look that you always end up with using AF assist. Anyway it sounds like for for those situations the 5D will win hands down, I was aware of all the IQ advantages in low light but didn't know how the AF held up there.


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## PeterJ (Dec 16, 2011)

Just thought I'd post back and thank everyone for their advice, as of today I'm a proud 5D Mk II owner ;D. I haven't had a chance to take any especially interesting shots but gave it a test under varying conditions and I can't find much difference in the center focus point speed / low-light perfomance versus a 7D. As some commented the outer spread of focus points is not great (well pretty bad), and I tried to repeat a shot I'd taken recently through a bird cage using spot focus that it couldn't match, but I expected as much.

Now for the good part is that banging on a tripod and taking a few food shots the colour reproduction was fantastic. Outside during the day the FF gave my 70-200 a much better focal range and shallow depth of field for the style of photos I often take. Got some nice shots at night too using a 50/1.4, I expected a nice ISO boost but it seems to handle dramatic changes in contrast much better too. I'm a happy camper and look forward to giving it a good run over Christmas. It will really complement my 7D well rather than replace it .

About my biggest gripe so far is the location and type of power switch, I saw a post recently by someone asking about how to extend the standby time. I didn't reply but thought why can't you just turn it on & off between shots but now see where he was coming from. I put mine of a tripod earlier and just about needed a screwdriver to get at the switch :.


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## Cyclops (Dec 16, 2011)

I just got my 5D a few weeks ago, and comparable the button layout (power switch) is much better on the 7D. Took me a long time to find the quick menu on the 5DIII, and takes a while to activate, and that menu is why i like my 7D.


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