Viewfinders and Autofocus Points
Posted September 29th, 2008 @ 07:23pm by Erik J. Barzeski
JDD talks about the autofocus found in the Canon 5D Mark II, and in talking with him, I told him that I agreed the 5D's focal points are pretty worthless. "Focus and recompose" doesn't work at paper-thin depth of fields, yet you're either forced to do that with the 5D or you're forced to zoom out, use the center AF point, and plan to crop later to obey the rule-of-thirds and get a focused image ((That's not to say you must always obey the rule of thirds, of course, but the majority of the time you probably want to heed the "rule.")).
I also told JDD that my ideal viewfinder and AF layout would consist of only five points.
Seen below, we have the 50D viewfinder, the 5D viewfinder, and the 1D Mark III viewfinder, each as shown to us by Canon. Note that the 50D, a crop sensor camera, uses the same autofocus screen as the 5D Mark II, yet despite costing half as much, features nine cross-type AF points. The 5D Mark II has only one cross-type AF point, along with six invisible ones. The 1D Mark III, needless to say, has a lot of sensors, and many are cross-type:
Below the three released cameras, I've drawn my own AF points and focusing screen (using this image of mine). My ideal layout would have the rule-of-thirds lines drawn on, with a cross-type AF point at each. I'd have a center AF point, surrounded by six invisible "helpers." And quite frankly, that's all I'd need. My requirements are lower than those offered by the 50D! I require less AF points than the 5DMII but more that are cross-type.
If I could really have my way, pie-in-the-sky style, I'd add the four AF points shown in red to really complete the package: nine AF points, five of which are cross-type, with six invisible AF assist points, positioned appropriately along the rule-of-thirds lines. Instant winner.
If you can think of a single reason why this "optimal" layout is worse than the one Canon will ship with the 5D Mark II (or which you can currently find on the 5D), you're more a more clever man than I. I've considered that lenses might not let in enough light at f/5.6 to reach out to the rule-of-thirds corners, but I don't quite buy it - not given their proximity to the cross-type sensors on the 50D.
In the end, Canon, I have a three-letter question for you: WTF?
I'm with JDD: the AF decisions made for the 5D Mark II are stunningly stupid from where I'm sitting. At the very least, why not give us nine cross-point AF points like the half-the-cost 50D?
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Posted 29 Sep 2008 at 11:20pm #
I think the problem with your suggested AF sensor layout is for any kind of tracking shooting, the points would be way too spread out to keep anything close to consistent focus on the same object. Think that is why most pro cameras have gone towards lots of AF points so the object is more easily tracked as it erratically moves around.
If all you shoot is the center point, the 5d Mk II should be pretty strong with the hidden AF points especially. But if you are going for rule of 3 shots, I agree, it will be a lot more challenging.
Think folks that are aware of the rules of 3 will figure it out, regardless of what AF system is in play. Some cameras are obviously easier for this purpose than others.
I don't get the lack of cross-point sensors more than the sensor layout. But I also don't understand the complexities in extending an existing AF system with cross-point. Guessing 3 years is enough time ... Wondering what the end Canon engineering tradeoff decisions were for what features were in / out ...
Posted 30 Sep 2008 at 8:25am #
[quote comment="49890"]I think the problem with your suggested AF sensor layout is for any kind of tracking shooting, the points would be way too spread out to keep anything close to consistent focus on the same object.[/quote]
I don't think so. I don't know of a single person that uses every AF point for tracking. You select one point, stick it on your object, and keep it on your object. One point is one point - it doesn't matter where it is in the frame.
[quote comment="49890"]Think folks that are aware of the rules of 3 will figure it out, regardless of what AF system is in play. Some cameras are obviously easier for this purpose than others.[/quote]
But that's the thing: the AF points are the same as they are on the 5D, and they're pretty useless. Only the far left and right one come close to "rule of thirds" use, and they pretty much stink in low light situations. So if they've had three years to figure it out already and haven't been able to make it work, I doubt three more will do much good.
[quote comment="49890"]But I also don't understand the complexities in extending an existing AF system with cross-point. Guessing 3 years is enough time.[/quote]
Especially given the 9 cross-type AF points on the cheaper 50D… which uses basically the same AF point layout.
Posted 26 Feb 2009 at 3:41am #
I totally agree with your optimal AF screen. THIS IS THE SAME THING I WANT and I'm looking for! This change would be the biggest request from me for Canon to fix on any new cameras. When Shooting with my 1.2f lens, I can't afford to use only the center point. The reason is because by the time I focus and recompose my shot the subject has already moved out of the focal plane and has become blurred. SO in conclusion this rule of thirds AF screen is A MUST HAVE FOR ME!.