Auto focusing

[Hanmin147]

Hi, my aunt just passed down a canon 400D to me as she is upgrading. This is not the 1st time I am handing a DSLR camera but when I select the auto focus mode to single shot, the camera always fails to focus. The images become out of focus and I am forced to shoot in AI Servo mode with burst shots. I was wondering if the problem lies with the lens or camera.
Ps I am shooting with a 17-85 mm USM lens.

 

[David Kwok]

When you half depress the shutter release, do you hear a faint motor sound when you place your ears against the lens ? Since you say u r using a USM lens, it means the motor is inside your lens. But of course focusing is done by your body AF sensors. I know for nikon, it is possible to NOT INITIATE auto focus when half-depress the shutter release, check your Canon DSLR that it has such a feature and it is activated. I believe Canon DSLR have such AF-ON back button.

I set my Nikon gear as such because I dislike my focus changing each time I half-depress my shutter release.

Hi, my aunt just passed down a canon 400D to me as she is upgrading. This is not the 1st time I am handing a DSLR camera but when I select the auto focus mode to single shot, the camera always fails to focus. The images become out of focus and I am forced to shoot in AI Servo mode with burst shots. I was wondering if the problem lies with the lens or camera.
Ps I am shooting with a 17-85 mm USM lens.

 

[Hanmin147]

When you half depress the shutter release, do you hear a faint motor sound when you place your ears against the lens ? Since you say u r using a USM lens, it means the motor is inside your lens. But of course focusing is done by your body AF sensors. I know for nikon, it is possible to NOT INITIATE auto focus when half-depress the shutter release, check your Canon DSLR that it has such a feature and it is activated. I believe Canon DSLR have such AF-ON back button.

I set my Nikon gear as such because I dislike my focus changing each time I half-depress my shutter release.

Yes it is set on auto focus on. I reckon it's the AF points on the body. Most likely upgrading to a 600D at the end of the year. Post production is hell if I use AI Servo (continuous) and burst shots to make sure a get a sharp photos.

 

[David Kwok]

Yes it is set on auto focus on. I reckon it's the AF points on the body. Most likely upgrading to a 600D at the end of the year. Post production is hell if I use AI Servo (continuous) and burst shots to make sure a get a sharp photos.

I don't quite get you. You seems to be complaining that your camera + lens combination fails to focus for single shot mode. So do you mean the lens is not focusing or what ? If you says it's focusing in Continuous Mode, it seems to me that there is nothing wrong with the AF sensors nor the lens focusing motor. In the firmware, it's possible to set that in continuous mode, re-focusing continue even while the capture is in progress, which coincide with what you are experiencing now.

If auto-focus is only assigned to the AF-ON button and not to the shutter release, then AF will not be activated even when you half-depress the shutter release button.

 

[ZerocoolAstra]

Yes it is set on auto focus on. I reckon it's the AF points on the body. Most likely upgrading to a 600D at the end of the year. Post production is hell if I use AI Servo (continuous) and burst shots to make sure a get a sharp photos.

It would help greatly if you answered the questions that David asked, coz he's trying to help you get to the root of the 'problem' you are facing

Going off on a tangent about it being hell ______ is rather unnecessary
How did you even come to the conclusion that it's the "AF points on the body"?

 

[Rashkae]

Yes it is set on auto focus on. I reckon it's the AF points on the body. Most likely upgrading to a 600D at the end of the year. Post production is hell if I use AI Servo (continuous) and burst shots to make sure a get a sharp photos.

I think you should not jump to conclusions. What exactly is it you are shooting? Are you or your model/target moving? When you say "the camera fails to focus", do you mean it keeps hunting back and forth for focus, or that it gives you focus confirmation but then the picture is out of focus?

 

[SkyStrike]

I don't quite get you. You seems to be complaining that your camera + lens combination fails to focus for single shot mode. So do you mean the lens is not focusing or what ? If you says it's focusing in Continuous Mode, it seems to me that there is nothing wrong with the AF sensors nor the lens focusing motor. In the firmware, it's possible to set that in continuous mode, re-focusing continue even while the capture is in progress, which coincide with what you are experiencing now.

If auto-focus is only assigned to the AF-ON button and not to the shutter release, then AF will not be activated even when you half-depress the shutter release button.

on top of this, if you do not have any settings on the camera, do a "reset all settings" to see if it works. It SHOULD AF correctly out of the box.

 

[Octarine]

TS: what is your AF point selection? Center AF or Auto AF across all possible AF points? Also: what are your shooting conditions? Light? Static subject or moving? It's useless to ogle at supposedly better models if you do not clearly determine the root cause of the problem. If the problem is behind the viewfinder no camera upgrade will help.

 

[Hanmin147]

Sorry for the confusion, let me clarify. When shooting a still subject, the camera fails to focus on single shot mode. Meaning that it keeps going back and forth trying to focus. It's an old camera so I suspect that is the problem.
Sorry again for the trouble caused. Thanks so much for the help.

 

[Bukitimah]

Hanmin147, the quickest way to find out is to set everything to auto mode and aim at a distance object. If the auto focus is still unstable, best to send it for checking.

If it cost too much, then either you use manual focus or it may not worth the $ to repair.

 

[David Kwok]

Sorry for the confusion, let me clarify. When shooting a still subject, the camera fails to focus on single shot mode. Meaning that it keeps going back and forth trying to focus. It's an old camera so I suspect that is the problem.
Sorry again for the trouble caused. Thanks so much for the help.

Erm. sounds like a faulty AF unit. The phase detection component is faulty. When your mirror is down, DSLR uses phase detection method of focusing. This method is faster than contrast detection. I suspect contrast detection is used in the sensor during continuous mode to achieve overlap focusing which is why you are still able to focus in that mode.

As a last resort, can you check that your mirror is clean ? Also check that towards the top of the mirror that there is nothing blocking for focusing.

If not, looks like a trip down to the service centre is necessary to fix it.

 

[eleveninth]

Erm. sounds like a faulty AF unit. The phase detection component is faulty. When your mirror is down, DSLR uses phase detection method of focusing. This method is faster than contrast detection. I suspect contrast detection is used in the sensor during continuous mode to achieve overlap focusing which is why you are still able to focus in that mode.

Looks like a trip down to the service centre is necessary to fix it.

Wah. U sound very well read! Lols

Btw how u know its not the focus distance?

 

[David Kwok]

Wah. U sound very well read! Lols

Btw how u know its not the focus distance?

Are you mocking me ? :bsmilie: Just kidding..

I won't say I'm well read, just that I'm a science person. Base on what TS described, if the issue is because of focusing distance or focus motor, then how can he possibly achieve focus in AF-C mode ? So I rule out the possibility that it's due to misuse of the equipment. In the last description, TS mentioned that in AF-S mode and the lens is hunting up and down to attempt focus. One possibility is there is nothing to focus such as a lens cap on or excessive dim lighting, the other is focus point is not set on something to focus on. Now the first is out because TS managed to focus in AF-C, the 2nd is unlikely because even if TS doesn't know how to use DSLR, it would at least catch something in the background or foreground to focus, instead of going back and forth.

Next is TS did mentioned he is not new to DSLR, so I'm not going to assume he is totally unaware that he need to point the focus point at the subject or too close to focus. The clue that allow me to make that conclusion is he managed to focus using AF-C and not AF-S. I have did a quick lookup on Canon 400D and it did equip with phase detection feature and seemingly coincide with the symptoms that he is describing.

Of course, I'm not totally convinced yet. Hence I ask him to check if there is anything blocking light between the lens, mirror and the top translucent thingie which is suppose to lead to the AF unit.

As a disclaimer, I don't repair cameras and I don't take them apart too. Not that wealthy to do something like this. :bsmilie:

I do like to read up on photography and its related technicalities hence I am quite informed in how camera does focusing for both phase detection and contrast detection.

 

[eleveninth]

Nope not mocking. Just using my iphone on the crapper.

dude tl;dr! Are u from jc?

Good job tho, this place needs more helpful ppl like you!

 

[David Kwok]

Nope not mocking. Just using my iphone on the crapper.

dude tl;dr! Are u from jc?

Good job tho, this place needs more helpful ppl like you!

I was from JC. That's like donkey years ago if you realize how old I am now ? keke
Thanks, it's my pleasure and honour to contribute to this community

 

[Rashkae]

Erm. sounds like a faulty AF unit. The phase detection component is faulty. When your mirror is down, DSLR uses phase detection method of focusing. This method is faster than contrast detection. I suspect contrast detection is used in the sensor during continuous mode to achieve overlap focusing which is why you are still able to focus in that mode.

Nope, if you fire in burst mode, the Canon DSLR cameras will flip the mirror down after each shot, re-focus, then shoot again, then repeat. It does not use CDAF.

 

[David Kwok]

Nope, if you fire in burst mode, the Canon DSLR cameras will flip the mirror down after each shot, re-focus, then shoot again, then repeat. It does not use CDAF.

That's possible. But any information you have found that the camera cannot use both the CDAF and PDAF together ? I don't seems to be able to find substantial information regarding when they will use CDAF except its definitely used in live-view mode.

@TS:
1) Are you able to produce sharp and focused images when you are using AI Servo mode ?
2) If you can try using manual focus, using the Canon in-focus indicator(bottom right dot) in the viewfinder. Does it works to show that you are in focus when you manually focus using the lens ? If so, are the images sharp ?

 

[Rashkae]

That's possible. But any information you have found that the camera cannot use both the CDAF and PDAF together ? I don't seems to be able to find substantial information regarding when they will use CDAF except its definitely used in live-view mode.

You're referring to newer Canon bodies...
In bust mode it will use PDAF. In single-shot liveview mode, it uses CDAF but it's soooo slow (can take 3-4s to focus). Do note that the TS's 400D is essentially "ancient" and does not even HAVE liveview.

 

[Hanmin147]

Erm. sounds like a faulty AF unit. The phase detection component is faulty. When your mirror is down, DSLR uses phase detection method of focusing. This method is faster than contrast detection. I suspect contrast detection is used in the sensor during continuous mode to achieve overlap focusing which is why you are still able to focus in that mode.

As a last resort, can you check that your mirror is clean ? Also check that towards the top of the mirror that there is nothing blocking for focusing.

If not, looks like a trip down to the service centre is necessary to fix it.

I will definitely take a look at the mirror later on. Thanks for all the help

 

[Hanmin147]

That's possible. But any information you have found that the camera cannot use both the CDAF and PDAF together ? I don't seems to be able to find substantial information regarding when they will use CDAF except its definitely used in live-view mode.

@TS:
1) Are you able to produce sharp and focused images when you are using AI Servo mode ?
2) If you can try using manual focus, using the Canon in-focus indicator(bottom right dot) in the viewfinder. Does it works to show that you are in focus when you manually focus using the lens ? If so, are the images sharp ?

Yes I am able to get sharp shots. But when I use AI Servo 1 out of 2 shots are sharp, the other one is out of focus.
In manual focus the photos are sharp, I will head home to try the in camera indicator.
Thanks everyone for helping me troubleshoot the problem.