Size of autofocus "points" on 40D and 5D vs. 10D

[istvan_sandor]

Hi,

Could anyone give me some information about the difference of the size of the

autofocus points on the 40d and the 5D? Are those smaller than on 10D ? I'm

especially curious about that regarding the center point which is painfully

large on the 10D.

For me, this would be one of the most important factors to consider an upgrade.

[jon_austin]

I can't answer your question, but with all due respect, I also can't imagine why this would be your most important upgrade factor.

 

Assuming that the autofocus points were identical in size on both bodies, the cumulative benefits of all the other improvements in the 40D over the 10D make upgrading a no-brainer ... if in fact you wish to upgrade.

[nkag]

everyone has their own reasons...

[istvan_sandor]

Jon: The reason why I consider it to be important is that - at least AFAIK - the smaller the autofocus point is the more precisely it can lock on what you want it to.

The center focus point (or rather area) on the 10d is large and this is a regular cause for misfocus.

Someone correct me if I'm wrong...

[danield]

Well, the way the AF sensors work is to maximize micro-contrast across the entire the sensor area. The area is usually small enough so that once a focus is achieved everything is in satisfactory focus due to the DOF of the lens.

 

You may be thinking that the square blinking in the viewfinder is the same as the AF area - this is not the case! The AF sensors are much smaller, the blinking square is just an indication of their position.

 

If you are having miss-focus problems with the 10D then something else is wrong, I wouldn't blame it on the size of the AF sensor. Are you looking at images at 100% magnification? Can you post a sample with Exif data?

[lester_wareham]

"The reason why I consider it to be important is that - at least AFAIK - the smaller the autofocus point is the more precisely it can lock on what you want it to. The center focus point (or rather area) on the 10d is large and this is a regular cause for misfocus."

 

No I agree with you. It is reasonably well known the AF points area of sensitivity is larger than the marked area in the viewfinder, there are probably sensitivity contours that diminish as you go away from the fp.

 

With a 20D I have noted a tendency to missfocus with a very small target although this may fill the apparent fp, I suspect this is due to fp overspill from the background pulling the AF phase measurement.

 

This is of practical import for wildlife subjects that may be small in the frame an need cropping.

 

I would be interested to see sensitivity contours for the focal points for various cameras, I don't know if Canon publish these but I am sure I have seen an example once.

[lester_wareham]

"The AF sensors are much smaller, the blinking square is just an indication of their position."

 

That is not my understanding Daniel, quite the reverse, and the first time I have heard this view. Have you a reference to demonstrate this?

[mendel_leisk]

Having had a 20D, and now a 5D, my take is that both cameras focus point clusters are the same size, except that it is shrunk down on the 5D, due to the 1.6 crop area has been added around the edges. The net effect is when you look through the 5D viewfinder the focus points seem much closer together, with much more space beyond.

 

I always use just the center point, and I find I'm often guessing (incorrectly as often as not) as to which one it is. Especially in low light, I'll resort to tentative focus, just to figure out which is which. I do wish the center point was differentiated somehow.

[andy_jones2]

Check this out - this is one of an increasing number of reports that the 40D has better AF

than its predecessors in the XXD range

http://www.bobatkins.com/photography/digital/canon_eos_40D_review_4.html

[alan_myers]

Hi Istvan,

 

I have 10D and 30D. I know what you are asking about. The AF indications in the viewfinder of the 10D *are* huge boxes! There are dramatic differences with the later cameras and AF is noticeably improved overall.

 

The AF points are much smaller, brighter and nicer to work with on the 30D. I am fairly certain they are quite similar on 20D, 5D and 40D. I don't have one, but am pretty sure the 20D improved a lot over the 10D in this respect and all the subsequent models just followed on or further improved upon that. The 40D appears to represent another step forward in AF capability.

 

However, as noted, AF points are often not entirely indicative of the exact area of the AF sensor. In that respect, the 10D viefinder might have been more "honest". In other words, the actual area being covered by each sensor may be closer to what's shown in the 10D's viewfinder, while the smaller points of the later models more are indications of the center of the focusing sensor area, than an an exact indication.

 

The sensors can also not be absolutely, perfectly aligned with the indications in the VF. Some slight skew is rather common among AF cameras. (See Popular Photography magazines camera reviews where they often test for this and usually illustrate it. They have many reviews online.)

 

So, it's a matter of learning the area of sensitivity around the indication in the viewfinder, but that becomes second nature pretty quickly.

 

The 40D sounds ideal, with all 9 sensors being the higher sensitivity cross type like used to be used only in the center point of the all the earlier models (plus the 40D's center point is also improved).

[danield]

"That is not my understanding Daniel, quite the reverse, and the first time I have heard this view. Have you a reference to demonstrate this?"

 

Actually, you may be right. I'm not well informed - I just always thought that the AF sensors were very thin strips, sometimes placed in a cross pattern to cover more area. But reading more on the web I seem to find different views. I wish a reliable source could clarify this.

[bobatkins]

The red AF zone indicator is just an indicator. The actual AF zone may be slightly displaced and slightly larger.

 

AF zone size is a very minor issue though. How well it works is much more important and I can tell you that the AF system on the 40D is definitely better than that on the 20D. It grabs onto low contrast detail better and and it seems to work better in lower light.