1Ds3 AF: learning to understand how it works

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Daan B
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p.4 #1 · 1Ds3 AF: learning to understand how it works

Jeff wrote:
I'm not sure why a 'more advanced' AF system would require an edge to get accurate AF.

Probably because it has smaller AF sensors and reads contrast differently in comparison to xxD and xxxD series AF. Both smaller and bigger AF sensors each have their own advantages and disadvantages. In a way it is like comparing apples to oranges.

Anyway, since it is obvious that placing the AF sensor on top of the tree doesn't give a in-focus shot with a mkIII AF, it is better to aim for the edges. Wether we like it or not. This is how it seems to work the best (with proper working mkIII's)

Edited on Aug 17, 2008 at 12:51 PM

Aug 17, 2008 at 12:50 PM

jamesf99
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p.4 #2 · 1Ds3 AF: learning to understand how it works

Daan B wrote:
FWIW

I redid the shots I posted in the OP using the following methods:

1) focus in the middle of the chimney using One Shot with the following C.Fn settings:
C.FnIII-8-0 (disable AF point expansion): still OOF
C.FnIII-8-1 (enable AF point expansion L/R): still OOF
C.FnIII-8-2 (enable AF point selection area): still OOF

2) focus in the middle of the chimney using AI Servo with the following C.Fn settings:
C.FnIII-8-0 (disable AF point expansion): still OOF
C.FnIII-8-1 (enable AF point expansion L/R): still OOF
C.FnIII-8-2 (enable AF point selection area): still OOF

3) focus on the edge of the chimney using One Shot with the following C.Fn settings:
C.FnIII-8-0 (disable AF point expansion): IN FOCUS
C.FnIII-8-1 (enable AF point expansion L/R): Some in focus / some oof
C.FnIII-8-2 (enable AF point selection area): still OOF

4) focus on the edge of the chimney using AI Servo with the following C.Fn settings:
C.FnIII-8-0 (disable AF point expansion): IN FOCUS
C.FnIII-8-1 (enable AF point expansion L/R): IN FOCUS
C.FnIII-8-2 (enable AF point selection area): still OOF

At shorter distances (like 10 meters/ 30 feet and less) the AF is doing fine when the AF point is placed over/on top of the subject. With longer shooting distances (infinity) the only reliable way to get good focus is to aim for edges, rather than placing an AF point over/on top of the subject. The effect of enabling AF point expansion when focusing at longer distances with both aiming tactics (placing the AF point over/on top of the subject and placing the AF point over the edge of a subject) and using both One Shot and AI Servo is nihil (except for enabling L/R expansion in AI Servo - but this seems to have little benefit over disabling AF point expansion). YMMV

Helpful post Daan.

I've long been used to focusing on objects that may not be my main subject or focal point. I "almost" always look for contrast first, understand my DOF vis-a-vis my aperture second, and then choose where to focus the camera. I've done this for many years, whenever possible that is, regardless of whether I'm using a 1 series or something less (especially with manual focus lenses because it's easier).

I think the best result of the Mark III fiasco (that's both the 1D and 1Ds) could be Canon's willingness to admit they pooched it. I've given up on the Mark III series and don't think I'll buy another (at least for a while), but since the IQ (when focused) is so good, I'd be willing to try again in the next "version" that will probably come out in 2009.

Aug 17, 2008 at 01:50 PM

Jeff
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p.4 #3 · 1Ds3 AF: learning to understand how it works

Daan B wrote:
Jeff wrote:
I'm not sure why a 'more advanced' AF system would require an edge to get accurate AF.

Probably because it has smaller AF sensors and reads contrast differently in comparison to xxD and xxxD series AF. Both smaller and bigger AF sensors each have their own advantages and disadvantages. In a way it is like comparing apples to oranges.

Anyway, since it is obvious that placing the AF sensor on top of the tree doesn't give a in-focus shot with a mkIII AF, it is better to aim for the edges. Wether we like it or not. This is how it seems to work the best (with proper working mkIII's)

Where has Canon detailed the information of the 1D MkIII's AF sensors being smaller than those in the 5D? I don't remember seeing that in the White Paper. I think the 40D White Paper had a statement about reducing pixel pitch in relation to the 30D, IIRC.

What I do remember is the fact that the MkIII's AF sensor(s) cover a significantly larger portion of the viewfinder than the area that the little red square presents. In other words, the little red squares are not accurate, as many of us have found with many cameras. How the 5D fares here, I have no idea. I'd love to know just how large an area beyond the red square it is, and if it impinges upon the area of other adjacent (assist) AF points.

I'm no engineer, but it sure sounds like there were a lot of ways to screw this new AF system up, and apparently Canon secretly implemented one of them.

Edited on Aug 17, 2008 at 02:17 PM

Aug 17, 2008 at 02:15 PM

jamesf99
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p.4 #4 · 1Ds3 AF: learning to understand how it works

Jeff wrote:

I'm no engineer, but it sure sounds like there were a lot of ways to screw this new AF system up, and apparently Canon secretly implemented one of them.

Secretly or unwittingly? Perhaps they implemented several ways..

Aug 17, 2008 at 02:23 PM

Jeff
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p.4 #5 · 1Ds3 AF: learning to understand how it works

Unwittingly, I'm sure, and from the sequence of events, I'd guess more than one, only one of which was 'easily' corrected. Once corrected, only then could it be shown that something else was going on, under limited shooting conditions or circumstances (I'm guessing deeper within the design of the AF system).

Edited by Jeff on Aug 17, 2008 at 07:30 AM GMT

Edited on Aug 17, 2008 at 02:30 PM

Aug 17, 2008 at 02:28 PM

Daan B
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p.4 #6 · 1Ds3 AF: learning to understand how it works

Jeff wrote:
What I do remember is the fact that the MkIII's AF sensor(s) cover a significantly larger portion of the viewfinder than the area that the little red square presents. In other words, the little red squares are not accurate, as many of us have found with many cameras. How the 5D fares here, I have no idea. I'd love to know just how large an area beyond the red square it is, and if it impinges upon the area of other (assist) AF points.

Of course I have no comparison to other 1D series cameras (or the 1D3 for that matter), but IMO the 1Ds3 AF red squares are covering the actual AF areas pretty tightly. When disabeling AF point expansion the red squares are very precise. You can test this pretty easily in AI Servo. Furthermore, I know for certain that the AF areas of the 5D are a lot larger than the actual red squares. How much larger I can't say for certain.

Edited on Aug 17, 2008 at 02:28 PM

Aug 17, 2008 at 02:28 PM

Jeff
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p.4 #7 · 1Ds3 AF: learning to understand how it works

Hmm. I know Canon has stated the the MkIII's red square is smaller than the actual area of the AF sensor, but I can't recall where (I'll post if I can find).

Aug 17, 2008 at 02:32 PM

jamesf99
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p.4 #8 · 1Ds3 AF: learning to understand how it works

Jeff wrote:
Hmm. I know Canon has stated the the MkIII's red square is smaller than the actual area of the AF sensor, but I can't recall where (I'll post if I can find).

I don't own/have a 1ds3, but from previous 1 series bodies some info should be n the "Metering Modes" section of the manual, along with a diagram of what area is covered by mode, CF, etc.

Aug 17, 2008 at 03:34 PM

Hrow
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p.4 #9 · 1Ds3 AF: learning to understand how it works

Jeff wrote:
Hmm. I know Canon has stated the the MkIII's red square is smaller than the actual area of the AF sensor, but I can't recall where (I'll post if I can find).

I don't know whether Canon has stated it or not but all you have to do is use the camera to know that red box represents only a portion of a particular focus sensor. In a lot of situations it is easy to fool the sensor - which while annoying, is just part of the process.

Aug 17, 2008 at 03:59 PM


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