40D Anomaly - DPChallenge Forums

09/19/2007 06:05:21 PM · #1

Well, I upgraded from Rebel 300D to 40D. While the camera is neat, I noticed an anomaly with the autofocus.

I used Tokina 12-24 and Tamron 24-135 lenses, and both yielded same results. If I use all 9 points for the AF, it never focuses on infinity, it maxes out at 2-3m. So even taking landscape shots at F8 or so photos are blury. However, if I switch AF to center focus point only, everything works fine. It focuses to infinity fine.

300D did not have that issue. Any ideas?

I will post few pics a bit later.

cpanaioti

Canon EF 70-300mm f/4.5-5.6 DO IS USM

09/19/2007 06:12:26 PM · #2

Is there anything in the frame that is in focus?

Photologist

Apple iPhone 14 Pro Max

Canon EF 70-200mm f/2.8L IS USM

09/19/2007 06:14:13 PM · #3

I haven't noticed this with my 40D, but then again, I'm yet to take infinity-length auto-focused shots. Have you tried this with other lenses? I'd try it with a Canon lens, just for kicks.

You may want to ask your question on the Canon Digital Photography Forums site. There are many very "Canon-knowledgeable" folks there.

cpanaioti

Canon EF 70-300mm f/4.5-5.6 DO IS USM

09/19/2007 06:15:23 PM · #4

Also, when all 9 points are chosen the camera is trying to get all objects under the 9 points in focus which may not be possible with the aperture at f8.

PhilipDyer

Canon EF 24-105mm f/4.0L IS

09/19/2007 06:16:41 PM · #5

I wouldn't be surprised if that's exactly how that focus setting is supposed to act. The thing I've always noticed about leaving all nine focal points on is that it very rarely captures the subject in sharp focus, especially at wider apertures. I don't think this is an anomaly with your camera, it's just the camera's best attempt at f/8 to get as much in the frame in focus as possible.

09/19/2007 07:15:38 PM · #6

OK, not the best pics, it was too dark when I got home. But here are some samples taken earlier.

Both F5, 1/50 at 24mm

9 point AF

Center point only AF

Nikon AF Micro-Nikkor 60mm f2.8D

09/19/2007 07:20:44 PM · #7

Originally posted by cpanaioti:

Is there anything in the frame that is in focus?

With 9 points nothing is in focus. With center only much better focus is throughout.

That's why I am not sure if it's me not knowing the camera, or if there's something wrong.

Thanks for replies.

David Ey

Nikon D80

09/19/2007 07:24:03 PM · #8

Originally posted by PhilipDyer:

I wouldn't be surprised if that's exactly how that focus setting is supposed to act.......it's just the camera's best attempt at f/8 to get as much in the frame in focus as possible.

yep, you is askin it to focus on too much dof

09/19/2007 07:39:18 PM · #9

OK, few more samples. I know, not exact same settings...

Center point AF, 1/100, F7, 24mm

9 point AF, 1/125 F9, 24mm

cpanaioti

Canon EF 70-300mm f/4.5-5.6 DO IS USM

09/19/2007 07:44:14 PM · #10

Originally posted by giega:

OK, few more samples. I know, not exact same settings...

Center point AF, 1/100, F7, 24mm

9 point AF, 1/125 F9, 24mm

For the 9 point AF shot it looks like the house in the background is the main focus.

For the center point AF shot the main focus is in the middle of the shot (duh) and the house in the foreground is slightly out of focus. The house in the background is fairly sharp.

Remember that the amount of the image in focus is 1/3 in front of the focus point and 2/3 behind.

For the 9 point AF shot with the focus on the house in the background, most of the image in focus is behind that house, very little in front.

Message edited by author 2007-09-19 19:57:10.

Canon EF 24-70mm f/2.8L USM

09/19/2007 08:07:12 PM · #11

Interesting things to consider. I am leaving for Germany on Friday, so I just want the pics to come out right. I'm taking 40D and I would like not to mess up too much :-)

Message edited by author 2007-09-19 20:08:21.

dwterry

Canon EOS-1D Mark III

09/19/2007 08:22:16 PM · #12

I don't have a 40D, and I don't know if the algorithm has changed from what I'm used to (300D, 20D, 5D and Mark III) but my understanding of the way Auto Focus works when you have more than just one AF point enabled is that the camera will search for the CLOSEST object and will focus on that.

So the problem is that your camera is not focusing "the subject of interest" in the photos (because it can't read your mind) and is instead getting something else.

I highly recommend NEVER using all AF points because you don't know what the camera will pick. Instead, always use a single AF point and stick it on what you want the subject to be in your photograph. You're the photographer ... why leave it up to the camera to figure out what the subject is?

dwterry

Canon EOS-1D Mark III

Canon EF 24-70mm f/2.8L USM

09/19/2007 08:31:13 PM · #13

There's a very good discussion on the workings of Canon's Auto Focus system here. Pulling a short but relevant quote from it:

You can either select one point or you can set the camera to choose its own points as you focus. If the camera chooses the points, it will usually focus on any number of points that are closest to the camera. About the only time this is better is when you're focusing on fast-moving activity that you can't keep under a single mark (say, a soccer player). Otherwise, it's usually better to select your own point. The diagonal points on the 20D are very close to the "Rule of Thirds" intersections, so sometimes it's convenient (if you use that composition rule to place your subject in the frame) to select one of those points."

09/19/2007 08:58:27 PM · #14

Appreciate the info. It was helpful.

splidge

Canon EF-S 17-55mm f/2.8 IS USM

09/20/2007 06:11:00 AM · #15

If you have all the points turned on, whenever you activate autofocus the points that the camera has chosen (and believes are now in focus) will flash. So you can check whether they correspond to the part you wanted in focus - and if they don't you can manually select a point to override it. As others have pointed out it, in most modes it will select the nearest object it can find to focus on.

Note that unless you have selected the "A-Dep" mode then it won't care about getting multiple subjects in focus, but will still flash multiple points if they are exactly the same distance away. In A-Dep mode it will try and get as much into the depth of field as it can (and flash the corresponding points).

Having played briefly with a 40D it seems the focus points are pretty good - so if there is something under one of the points which is nearer than the thing you actually wanted in focus then you're going to have to pick the point manually.

splidge

Simms

Canon EF 24-70mm f/2.8L USM

09/20/2007 06:39:59 AM · #16

Originally posted by dwterry:

Beat me to it.

Yup, when using all focus points the camera will find the subject closest to the camera and focus on that. I double checked using my 300D and 5D and it works identically on both.

Am I correct in thinking that the newer canons have facial recognition algorithms that will focus on faces in a scene? anyone had any experience of how it works? good/bad etc.

splidge

Canon EF-S 17-55mm f/2.8 IS USM

09/20/2007 06:47:02 AM · #17

Originally posted by Simms:

Am I correct in thinking that the newer canons have facial recognition algorithms that will focus on faces in a scene? anyone had any experience of how it works? good/bad etc.

The digicams do yes, my girlfriend has one. Seems to work pretty well (although I've not used it much).

This is not something that exists in SLRs yet, although with live view mode it becomes technically possible - it may even be feasible for Canon to add it to the digic III SLRs via firmware if needed. But more likely it will turn up in a generation or two's time as a differentiating feature.

splidge

glad2badad

DJI Mavic Air 2

Sears 55mm f/1.4 M42

09/20/2007 07:48:07 AM · #18

Originally posted by giega:

OK, few more samples. I know, not exact same settings...

Center point AF, 1/100, F7, 24mm

9 point AF, 1/125 F9, 24mm

Just an observation, but it seems that the 9 point AF is doing a better job of metering the exposure. Richer color.

09/20/2007 08:09:43 AM · #19

Originally posted by Simms:

Yup, when using all focus points the camera will find the subject closest to the camera and focus on that. I double checked using my 300D and 5D and it works identically on both.

I'll have to double check. I don't think I have experienced that with 300D. That's why I thought the focusing was different with 40D.

I feel educated now. :-)

AdrlnJunkie11

Canon EF 50mm f1.2L

09/20/2007 10:36:16 AM · #20

I'm having the same problem and I'm using a Canon 24-70mm f/2.8L so I know it's not the lens. I didn't have this problem with my 30D.

PhilipDyer