DSLR AF accurate in some modes, back-focuses in others?

[marchaprl]

Hello everyone,

I was hoping with the vast knowledge here someone could help me with an issue I've been having, as the manual and internet searches have not yet helped.

After stretching my p&s to its limits I jumped on the DSLR bandwagon with a Canon 40D. I purchased it used (so as to spend money on classes instead) and it came with a 28-90 and nifty-fifty. I read the manual and returned the camera to factory-settings so that anything from the previous user would be set back to normal.

In full automatic, "creative" modes (sports/landscape, etc) and C3 the camera focuses perfectly with both lenses nad gives the focus indicator "beep". In Av and Tv the camera consistently focuses behind the object I'm trying to get clear. To add to the mystery the camera also won't "beep" in these two modes.

I've tried specifying different focus points (center, and various outer ones). I've tried both Av and Tv in combination with single-shot AF, AI servo, etc. and they all seem to focus behind the subject.

I'm encouraged by the fact that it works in the more automatic settings, but the whole point of the DSLR is to go beyond automatic! I've been scouring the manual and the internet to learn and try and troubleshoot but to no avail.

Any suggestions as to what I may be doing wrong? I really appreciate any help I can get!

[David]

Hi Marchapril - Welcome to CiC. The short answer to query from one who owns a Canon40D is that I don't know what's wrong. My initial thought was that you've not reset the Custom Function III Auto Focus/Drive to 0. On zero setting the shutter release on half press focuses as well as assesses exposure. Set on say 1 the AF On button on the back of the camera does the focusing and the shutter release the evaluation. Thus, the shutter release in Av and Tv modes will not focus the lens. However, you say that you've returned everything to manufacturer's defaults so, if you've checked that Custom Function is back at default, that cannot be the answer.

Another thing to try is to see if the lenses focus correctly when you use Live View. I once thought that I got better focus on Live View and Manual focus than with auto focus.

You don't say whether the problem occurs on M mode, but you do refer to C3. C3 is presumable a custom setting that you've put into the camera. How about setting one of the other custom buttons (C1?) to a set of parameters that includes Av or Tv as one of the settings. See what happens then.

Others here may have encountered the problem and perhaps can offer further advice.

Cheers

David

[Jim B.]

I've not read about or experienced the problem you are having.
I'll second Dave's comment on using "back button focus".
Use a tripod when you test and shoot something with good contrast.Low contrast subjects will make AF difficult to achieve sometimes.

[Colin Southern]

Hi Marchaprl,

It really shouldn't be this hard!

Just some thoughts ... (so as to narrow down the options) ...

1. Ensure Lens set to AF, not MF

2. Ensure focus mode set to one shot, not servo

3. Ensure only 1 AF point is selected (preferably centre) (letting it choose it's own will normally focus on the closest thing, but it can be a bit of a lottery)

4. Ensure LiveView is OFF

5. Looking through the viewfinder, point at things at different distances - press the shutter release 1/2 way down ...

(a) Does the focus adjust?

(b) Do you get the AF confirmation light in the view finder?

(c) Do you get the confimation beep?)

PS: I'm assiming that you'll do the above with all the custom functions set to their defaults - some of them might change if you start re-mapping buttons etc.

[marchaprl]

Thank you all, the problem is solved! Apparently "Restore factory settings" does not affect the custom functions. So the half-depress of the shutter button was set to not auto-focus, and it didn't get reset since it was in custom functions.

After reading your post I went in and checked the custom functions and then I set all the customs to default (I'll adjust later when I know more about what I need) and everything worked as it should.

I can not even begin to describe how relieved I am, thank you so much!! Gray matter problems are so much easier to solve than hardware issues!

[Colin Southern]

Glad you like the service -- hope you'll stay a while

[RonH]

Glad you like the service -- hope you'll stay a while

Maybe a bit more service please, Colin, if you have time.

What are the benefits of multi-focus points? When taking a pic, I am looking to capture something specific and hence would like to make sure that this at least is in focus. I would set camera to single point (centre) focus and if wanted then shift the camera view whilst holding down the shutter button half way to lock focus.

I guess that for moving subjects, multipoint could perhaps be useful for focus tracking ... but I would be tracking with the camera.

Does anyone use multipoint and for what? Seems to me that the various manufacturers make a big issue of 'who has the most' so it must have significant value.

[Colin Southern]

Maybe a bit more service please, Colin, if you have time.

What are the benefits of multi-focus points? When taking a pic, I am looking to capture something specific and hence would like to make sure that this at least is in focus. I would set camera to single point (centre) focus and if wanted then shift the camera view whilst holding down the shutter button half way to lock focus.

I guess that for moving subjects, multipoint could perhaps be useful for focus tracking ... but I would be tracking with the camera.

Does anyone use multipoint and for what? Seems to me that the various manufacturers make a big issue of 'who has the most' so it must have significant value.

Hi Ron,

All modes and options have their place ... it just makes the camera more versatile so it appeals to a wider (paying) audience.

Letting the camera chose the AF points generally works OK for what I'll call "tourist mode" (kinda like a glorified P&S), but if you use it for, say, portraiture when you have a narrow DoF then you're likely to have the tip of the nose in focus - the eyes slightly soft - and the ears significantly soft. Personally I nearly always have just 1 AF point selected, although which point that is depends on what I'm shooting; for portraiture it's generally the one closest to the nearest eye.

Focus and recompose can bite you in the rear end if you have a narrow DoF and the distance changes between the focusing and the shooting. Say you're standing at one end of a bowling ally ... if you focus on YOUR pins and then recompose and shoot the pins in the adjacent lane then the distance has increased. So usually best just to use the closest AF point to what you want sharp.

Servo mode is a whole different story though.

[marchaprl]

A+ customer service Careful what you wish for in asking me to hang around though, the only thing I know enough to contribute right now is more questions!

I do start two photography classes this week though, a general beginner's class tonight and a "Night and Low Light" class tomorrow... hopefully after those I'll have some small bit of knowledge worth sharing!

[RonH]

Hi Ron,

All modes and options have their place ...

... Servo mode is a whole different story though.

Thanks Colin. I should have mentioned that for 'movement' I do use the Dynamic Area (Nikon term) which tracks what you are following ... or at least that's the theory