Daan B wrote:
True... but there is more to it... The AF point in the VF represents a much larger area than you can see in the VF.
That's true of all the points, and more true of the center point. The sensed area of the center point is about nine times the area of the viewscreen marking. The sensed areas of the rectangles are about three times the areas of the viewscreen markings.
So in that respect, the peripheral points are no different--no better and no worse--than the central point.
The pixel arrays that make up the peripheral focus points are not inferior arrays to those in the center. They are the same type of arrays, the same type of pixels, the same number of pixels in each array, the same technology, using the same system.
The only difference at less than f/2.8 is the physical orientation--being a single-orientation array, it's only half as likely to be perpendicular to subject linear contrasts.
RDKirk wrote:
That's true of all the points, and more true of the center point. The sensed area of the center point is about nine times the area of the viewscreen marking. The sensed areas of the rectangles are about three times the areas of the viewscreen markings.
So in that respect, the peripheral points are no different--no better and no worse--than the central point.
The pixel arrays that make up the peripheral focus points are not inferior arrays to those in the center. They are the same type of arrays, the same type of pixels, the same number of pixels in each array, the same technology, using the same system.
The only difference at less than f/2.8 is the physical orientation--being a single-orientation array, it's only half as likely to be perpendicular to subject linear contrasts. ...Show more →
Did you forget about the 6 invisible assist AF points surrounding the center one?
On top of that... less light will hit the outer AF points compared to the center AF point. The outer AF points are less sensitive (to light) in this regard. This is of course true for every camera. But it sure doesn't help that the 5D2 outer AF sensors are only single axis.
Daan B wrote:
Did you forget about the 6 invisible assist AF points surrounding the center one?
That's only in effect when AI Servo is on, and it does not change the level of accuracy--it reduces the likelihood of the camera losing focus on a moving subject.
On top of that... less light will hit the outer AF points compared to the center AF point. The outer AF points are less sensitive (to light) in this regard. This is of course true for every camera. But it sure doesn't help that the 5D2 outer AF sensors are only single axis.
No, that's not an issue. Canon has limited the area that they place the sensors to within the cone of light that they are within suitable limits--which is why there aren't any focus points farther than 15mm from the center in any of their cameras.
The only difference is the orientation. You can test it yourself: Switch on one of the peripheral points and turn the camera so that it's perpendicular to a strong line, like a door frame. Now dim the lights until you reach a light level so dim the camera can no longer focus on that perpendicular line.
When you reach the level of dimness that finally confounds the outer sensor, try to focus on it with the center point.
How many years have we had this AF system now and people are still confused about it? The outer points are pants because they aren't cross-type. RDKirk has given the more technical explanation, but that's really all it boils down to. Basically expect the center point to be able to lock on more quickly (or at all) in more circumstances than the outer points.
Yohan Pamudji wrote:
How many years have we had this AF system now and people are still confused about it? The outer points are pants because they aren't cross-type. RDKirk has given the more technical explanation, but that's really all it boils down to. Basically expect the center point to be able to lock on more quickly (or at all) in more circumstances than the outer points.
doesn't the center point also do high-precision 1/3 DOF instead of 1 DOF focusing unlike the outer points too?
I don't own any lenses slower than f2.0, so I don't buy the line that all the points are the same sensitivity, because clearly they are not for lenses faster than f2.8
I sprayed a little WD-40 onto a gauze pad and carefully went around the edges of the card door. Along with my own finger oils, sunscreen residue and some use over the last few months shooting - the squeak is gone. The door still flexes at bit, but silence is golden.
Mike V wrote:
I don't own any lenses slower than f2.0, so I don't buy the line that all the points are the same sensitivity, because clearly they are not for lenses faster than f2.8
+1
Like... when I use my 85L II @ f/2.8 (or larger), amd aim for an eye, using an outer AF point... it misses focus most of the time. When I do the same thing, but use the center AF point instead, I get everything in focus most of the time.
I am obviously no technician... but this can't be (entirely) explained by the difference in single axis vs cross type. Because an eye contains no straight lines and has both horizontal and vertical contrast.
Even though some have said otherwise, my best guess is that the outer AF points are less sensitive (to light -?-) than the center one.
Like I said earlier... for me it is no problem. I will either focus-recompose using the center AF point. Or just use the center AF point and crop afterwards. Plenty MP's to crop with.
Of course, it would have been better if the 5D2 had a all cross type sensors (of the same sensitivity). But it hasn't
My only nit...still doesn't have a 100% viewfinder (and maybe no external button for mirror lock up, although you can set it in one of the three custom modes, along with other settings). But like anything else, if one looks hard enough to find a flaw... Personally, considering the price/features/performance aspect, I find it to be one heck of a camera. Maybe I've just been lucky, but I have to have any issues with any Canon body or lens (unless I'm just not looking hard enough).
Mike Ganz wrote:
My only nit...still doesn't have a 100% viewfinder (and maybe no external button for mirror lock up, although you can set it in one of the three custom modes, along with other settings). But like anything else, if one looks hard enough to find a flaw... Personally, considering the price/features/performance aspect, I find it to be one heck of a camera. Maybe I've just been lucky, but I have to have any issues with any Canon body or lens (unless I'm just not looking hard enough).
98% isn't bad and you do have 100% instant review on the LCD
As far as mirror lock up, I just use Live view and the 2 second self-timer, that way I can check focus accurately too
Having just got one to complement my 1D III, I feel that it is going to be very few circumstances that I use the 1D, other than sports now (I don't do BIF or non landscape nature or aviation). I like it that much.
That said, I do worry I will miss the moment. There is a clear difference in the focusing speed -- which doesn't surprise me or necessarily bother me per se. There's currently a $1000+ difference between the two bodies new, and it was much more than that on release.
I do miss some other things, which I guess are possibly just hidden in the menus that I haven't found yet, a few of which are:
1. The well stated fact that the focus points are too clustered.
2. The fact that it doesn't appear in custom functions you can make taking the shot the priority other than focus lock.
3. Have exposure linked to the focus point.
4. Having the zoom to review linked to the particular focus point you selected.
I haven't used a flash yet, but I'm sure the synch speed will also affect me.
outer AF points are untrustworthy in low light
noise floor has a large scale criss-cross pattern visible in shadows at low isos
you still have to press play before zooming
you can't get spare batteries
the mirror sticks out further than it needs to
body geometry calibration may not be perfect
the power switch is in the wrong place
there is still no way of showing histograms superimposed on the full size image in review
contrast detect focussing is too slow
you can't choose the contrast detect and liveview magnify points by tapping a finger on the monitor
aim for an eye, using an outer AF point... it misses focus most of the time. When I do the same thing, but use the center AF point instead, I get everything in focus most of the time.
I am obviously no technician... but this can't be (entirely) explained by the difference in single axis vs cross type. Because an eye contains no straight lines and has both horizontal and vertical contrast.
Canon explains why in this quote from the 5D (I, not II) white paper, page 9:
Additionally, the center AF point’s f5.6-sensitive, horizontal line-sensitive sensors each have two lines with individual pixels arranged in a zigzag pattern, making a total of four lines for horizontal line-sensitive focusing at the center. With this improvement, the center AF point can now do a better job of detecting difficult-to-read, low-contrast subjects, thus improving the overall performance of the autofocusing system.
brainiac wrote:
noise floor has a large scale criss-cross pattern visible in shadows at low isos
i actually did some testing on this and combined with that done by a few others it seems that the 1dmkiii, 1dsmkiii, 40D generation were the kings of low banding pattern read noise at low ISO and that the 50D, 5DMkII generation is a step backward in that one regard, having as much as 2x the amount of ISO100 banding pattern read noise.
The new CFA filter array also make the chroma noise get a bit of a penalty on the new generation and the very low frequency chroma noise is worse than the prior generation.
The total read noise adjusted for MP difference though does seem a little bit less for the 50D than the 40D at ISO100, but the eye noticed pattern noise a lot more readily.
The 5DMkII, adjusted for MP difference, actually less total read noise at ISO100 than the 1DMkIII too, but almost 2x the pattern banding read noise.
Of course, a more real world comparison would be the DR at ISO100 and for that you also need to take into account the max level they can reach before saturation, which if not the same for the various cameras, would mean the read measurements alone won't tell the entire story)
anyway the 5DMkII is pretty fine camera and it's nothing to get too worried about, although it is a shame they didn't keep the prior generations level of low ISO banding pattern noise, but again nothing to get too worried about and I hear it has less than the old 5D.
in fact is more than pretty fine, it is a truly awesome camera (so long as you don't have to have fast mirror/fps)
skibum5 wrote:
i actually did some testing on this and combined with that done by a few others it seems that the 1dmkiii, 1dsmkiii, 40D generation were the kings of low banding pattern read noise at low ISO and that the 50D, 5DMkII generation is a step backward in that one regard, having as much as 2x the amount of ISO100 banding pattern read noise.
The new CFA filter array also make the chroma noise get a bit of a penalty on the new generation and the very low frequency chroma noise is worse than the prior generation.
The total read noise adjusted for MP difference though does seem a little bit less for the 50D than the 40D at ISO100, but the eye noticed pattern noise a lot more readily.
The T1i / 500D is just as good as the 40D regarding pattern noise and MP adjusted read noise, and seems a little better than the 50D regarding low frequency chroma noise.
I am obviously no technician... but this can't be (entirely) explained by the difference in single axis vs cross type. Because an eye contains no straight lines and has both horizontal and vertical contrast.
Au contraire. If you draw an eye on a piece of paper, you will find yourself drawing mostly horizontal lines--eyebrow and eyelids--and only very short sections of vertical lines. The eye is predominantly a subject of horizontal linear contrasts.
When you activate one of the far end peripheral sensors and turn the camera vertically for a headshot, then try to focus on an eye, you will have turned the camera to the very orientation that makes it most difficult to focus on the eye.
Turn that camera so that the rectangle is perpendicular to the eyelids and eyebrows, and you'll find the peripheral point is just as accurate as the center point. Sit down with the camera and try it.
The well stated fact that the focus points are too clustered.
They are as far from the center axis of the lens in absolute millimeters as any other DSLR camera. This is a limitation of optical geometry to which all of the cameras are subject.
