50D Back from Canon - Focus lost when re-compose shot

Never test camera focus issues on a object that can move. When testing a camera for focus issues never shoot slower than 2 to 3x slower than the focal lenght you are using unless you have the camera on a quality tripod and are using timer mode or a remote shutter release. Never test focus issues with a camera set to any other mode except for single shoot, center focus point only unless you are testing for something specific to another option.

You do realize that the camera doesn't know you moved it don't you? You could focus lock on a specifc spot, recompose, and then recompose back onto the initial spot and the camera wouldn't know it. You can put your camera on a tripod, focus lock, remove your finger, and turn the lens to manual focus and the spot you focused on should still be in focus.

All that being said, retest your 50D with a more stable subject and with a tripod if at all possible to prevent any chance that you are moving your camera a little forward or backward.

Good luck.... hope it works out.

John
--

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Reply - quote ---

You do realize that the camera doesn't know you moved it don't you? You could focus lock on a specifc spot, recompose, and then recompose back onto the initial spot and the camera wouldn't know it. You can put your camera on a tripod, focus lock, remove your finger, and turn the lens to manual focus and the spot you focused on should still be in focus.

Yes, Yes and Yes because in all of those instances you have kept your focus on the same spot - recomposed putting it back to the same spot .

I am trying to focus on an object - for example - I did the same test today on an unmoving object in the garden - a tile with a flower motif infact - focussed on the centre of the flower then re-composed so the flower pot was not central to the shot - I lost focus on the tile completely - focus just shifted to centre
I'm sure I am not explaining this properly

Tomorrow I start testing again - now I'm going to bed with my manual - we have a really good relationship!!!!

--
Jayboo
 
jayboo wrote:
I'm sure I am not explaining this properly
No you are explaining it perfectly. We (me for example) just find it hard to believe. But if it is so... then your camera needs to go back to Canon. If it is so and you say it is.... there is nothing we can do to help you. I am sorry about that.
Tomorrow I start testing again - now I'm going to bed with my manual - we have a really good relationship!!!!
Glad you are able to keep your sense of humor... in the big picture this is a small thing. Don't spend too many days testing your camera. Make up your mind one way or another tomorrow and do something. It is no fun having a camera that you can't use.

Keep us posted. We (me again) would like to help if we could, but maybe we can't.

John
--

Feel free to use any of these additional letters to correct the spelling of words found in the above post: a-e-t-n-d-i-o-s-m-l-u-y-h-c If you find any extra letters, please place them here for future use...
 
As already mentioned you've got to remove all other possible issues to test. Fast shutter speeds, non moving subjects etc to rule out the basics.

I know Canon service isn't perfect; I've had a new 100-400IS that had an IS module failure and what should have a simple repair turned into their technicians just unable to repeatedly put it back together with the result I ended up receiving a new lens.

The I sent in a 450D for occasional focus failure but otherwise IQ was great but the technicians solution was to adjust the focusing - it then no longer foced correctly with any of my lenses. They tried again, and again, replaced the camera with another 450D that had also been calibrated but it was the same as the previous camera - the story goes on and on with me going twice to Canon to demonstrate the problem.

The final result was that the service director arranged that I got a full refund from the dealer.

I now have a 50D that works perfectly with all my lenses so it's quite feasible that your problem has been caused by an assembly error but it's very important to remove all other possible user errors 1st.

http://www.pbase.com/maijay/450d_af_failure__miss_focusing&page=all
jayboo wrote:

Hmmm - perhaps its my eyes then - but to me the hair below the collar looks pretty well focussed - I agree shutter speed need to be faster - my object was to test if camera was holding focus when I re-composed - again I repeat - it did on the 450d not on the 50d

Whilst I myself can be critical on the shots and I agree with your comment - does that really explain why focus has shifted???

I am seeing the other comment about shift of focal plane when re-composing but I am not sure that totally explains results on the 50d shot - I can see that on the 450D shot however
--
Jayboo
--

 
Right - Shot this on AV Mode - with value of 7.1 - shutter 1/15 - Hands Up - not meant as a pun - I have not got the steadiest hands in the world and I can see where you are coming from
That is absolutely, positively the problem you're having here with getting the eye sharp. 1/15th of a second simply isn't fast enough. Quite frankly, at an f-stop around 7 (is that really what you're shooting this at?) you should have plenty of DOF here. At a reasonable focal length and subject distance (which it looks like you have here) you simply won't see OOF caused by that small a recompose at f7.

To accurately guage what's going on here, you need to shoot a sample with your lens wide open, to make the DOF as narrow as possible, and thus make the focal plane as easy as possible to detect.
  • however - that - maybe because I am THICK - still does not explain to me why the point of focus shifts when I re-compose the shot - unless you are suggesting my hands are extremely unsteady.
I'm a little confused by the problem you're describing here. Perhaps because you're using imprecise language.

There is a "focus point" - the red square in your viewfinder that lights up when the camera acquires focus. You've said you're using center-point, which means that this is in the center of your viewfinder.

There is a "focal plane" and a "focal distance" The "focal plane" is the plane parallel to the image sensor, which is exactly the focal distance away from the optical center of the lens.

(It is important to understand that you are dealing with a focal plane, not a focal sphere. This can cause some misunderstanding).

So I'm not sure what you mean by "point of focus."

Here's the problem with focus-recompose at wide apertures.

Let's say you focus on the dog's eye then recompose. The focal plane now moves, because it's a plane, not a sphere. The eye will now be SLIGHTLY in front of the plane of focus.

Now, a couple of months back I actually ran the math on this, and what I found was that, under most practical shooting conditions, even shooting fairly wide (f2.8 ... I may have checked even wider) that the focal plan moved so little during recompose that your image would be acceptably even if you recomposed the maximum possible amount (focusing at the center point, recomposing so that the object you focused on is now in the corner). For a typical recompose, along the lines of what you're doing here, you're simply not doing enough to take the eyes out of focus.

This problem is, however, unavoidable. And if shooting wide open on a very fast lens, it creates some problems. There are really two solutions:

The first is to focus-recompose from the nearest focal point, rather than from center point.

The second - which you'll see a lot of pro's do when focus is absolutely critical and DOF is very, very narrow ... is to focus manually. This is a non issue if you even have six inches of DOF, but slap a 50mm 1.2 lens on your 50D, get close to your subject and open all the way up, and, yeah ... it's an issue.

Again, at f7, however, I simply fail to see how this could possibly be the issue here.
 
Reply - quote ---
centre of the flower then re-composed so the flower pot was not central
to the shot - I lost focus on the tile completely - focus just shifted to centre
I'm sure I am not explaining this properly
Surely you're not talking about the red square not staying on your original point of focus? The red square just indicates which point was used to focus... not where the camera actually focussed when you move it to recompose.

--
-- Doug

Galleries: http://picasaweb.google.com/dsmoak/
 
Yes, Yes and Yes because in all of those instances you have kept your focus on the same spot - recomposed putting it back to the same spot .

I am trying to focus on an object - for example - I did the same test today on an unmoving object in the garden - a tile with a flower motif infact - focussed on the centre of the flower then re-composed so the flower pot was not central to the shot - I lost focus on the tile completely - focus just shifted to centre
Let's walk this through slowly.

You are in one-shot focus. The camera is set to center-point only.

You push the button halfway, and the little red center square on your camera lights up briefly, correct? Your camera may also beep at this point if beep is on.

You then recompose the image, by pivoting the camera (but moving it as little as possible) so that the tile is now in the corner of the frame, correct?

You have not released the shutter button, correct? It's been halfway-pressed all this time? You do not see your center square flash again, correct?

You push the shutter the rest of the way, and it takes the picture, correct?

What it sounds like is happening is that you are releases and re-pressing the shutter button, so the camera re-acquires focus. This is a big part of why a lot of us prefer back-button focus, where focus is achieved by pressing the AF-ON button, and the shutter release has nothing to do with it. You'll know this is going on (if you're in one-shot focus!!) if you see the center square flash red again, and the camera beeps again (if set to beep).
 
At very close focus distanses even f7 is not enough to ensure focus when you do a focus-recompose but then we are talking almost macro shots (I can't see the focal length used in these pictures but it doesn't seem like ultrawide at least, but pretty close to subjrect, no?)

It seems the OP is on-top on things but in his shoes I would ensure myself that the lens/camera combo works w/out the recomposition part to start with. If the camera/lens is able to focus correctly on a stationary object (no recompose) then everythings is fine and the only thing needed to be improved is the recompoition technique. The 50D has the lens micro focus adjustment that should be used as well, especially when comparing same lens with another camera body

cheers
Biggis
 
Due to the semantics of how this has all been posted, I'm still not convinced that I understand exactly what the OP is saying.

When you lock focus by half-pressing the shutter release button, (or better yet, using the AF-On button) the chosen AF point is used to make a measurement of how far to adjust the lens focus. The lens then moves to that position.

If you do "stutter" on the half-press of the button, the system will focus again on every subsequent "make" of that button contact. So as was suggested, you could be getting a "refocus" accidentally. So it IS a lot better to divorce the AF from the half-press of the shutter button, and instead always use the star button or the AF-On button. That eliminates the possibility of the shutter button causing an unintended refocus.

But I'm still not clear what the OP expects. When the manuals talk about the focus staying where you placed it, what they mean is that barring a re-activation of the AF system (a second half-press of the shutter button in this case), the lens simply will not focus again. So the little red rectangle won't move, it won't "track" the eye of the dog, for example.

When you view in a program that shows the selected AF point, the center AF point will always show up in the very center of the frame. It won't somehow track the eye and stay on the eye.

And in addition, if you focus on the eye, lock focus (don't let the AF motor operate again) and then recompose, you need to realize that the eye may not end up being in good focus after the recomposition. That's because most modern lenses have a flat field of focus. They focus on a plane, not on a sphere.

So, for example, you can shoot a photo of a brick wall, and one focus setting will result in the whole wall being in focus IF you're aimed straight on to the wall.

But we know that the wall near the edges of your photo was farther from the camera than the wall near the center of the photo. So the field of focus is NOT equidistant from the lens. It's a flat plane.

Now, if you focus lock recompose, you're rotating that plane of focus when you move the camera. That means that the eye won't lie in that plane any more. So focus lock recompose is NOT good for critical shots with shallow depth of field.

If you're shooting a portrait at a large aperture (low f/number) you must focus manually after setting the camera position. If you recompose after focusing, you're asking for trouble.



But, in the sample photos posted, it looks like motion blur was the main problem. And keep in mind that if the dog moved, his collar area may have been stationary while his head moved a lot! So that would explain what you're seeing.

You have to eliminate all variables except for the one you're testing for any experiment to be valid.

Shoot at a high shutter speed (at least 1/250th) to keep motion blur to a minimum. Be sure to compare shots taken at the same aperture setting with the same lens. Be sure to compare images at the same size (not at 100%).

Don't expect the red rectangle to track anything. If you recompose after locking focus, the focus point will still show up dead center in the frame because that's the sensor you used when you locked focus.

Don't be discouraged by rude responses on here, either. Just ignore the posts made by impatient people. Life is too short, you know :)

Try setting C.Fn IV-1 = 3. That removes autofocus from the shutter button. Now, you use the AF-On button for AF. You press the AF-On button, the camera focuses, you take you finger off that button, and the lens stays set where you left it until you press the AF-On button again. I prefer this because I can lock focus with one "aim", lock exposure with a different "aim", and shoot the photo with a third "aim".

--
Jim H.
 
Thank you for your response - and I agree I need to be more sure it is the camera not my handling of it.

The fact remains though that when I first had this camera I was thrilled and delighted at some of the results I got - whether by accident or concentration on my part.

However, since it came back from Canon for the last repair I have not been happy with a single shot.

It is worrying for a newcomer to photography like myself that you can invest hard earned cash, more importantly many many hours - which should be fun ( it is really) and that there is a chance Canon got it wrong. If I was an expert and got a faulty camera - then I would know straight away - for someone like me - its just a niggle, you feel foolish.

Well today I am going to give it my all and try all suggestions - I'm kind of hoping it is me - what you went through sounds horrendous
thanks again
--
Jayboo
 
Never test camera focus issues on a object that can move. When testing a camera for focus issues never shoot slower than 2 to 3x slower than the focal lenght you are using unless you have the camera on a quality tripod and are using timer mode or a remote shutter release. Never test focus issues with a camera set to any other mode except for single shoot, center focus point only unless you are testing for something specific to another option.
You do realize that the camera doesn't know you moved it don't you? You could focus lock on a specifc spot, recompose, and then recompose back onto the initial spot and the camera wouldn't know it. You can put your camera on a tripod, focus lock, remove your finger, and turn the lens to manual focus and the spot you focused on should still be in focus.

All that being said, retest your 50D with a more stable subject and with a tripod if at all possible to prevent any chance that you are moving your camera a little forward or backward.

Good luck.... hope it works out.

John
Today I will be taking shots of bottle on cans - on a table outside - in the shade - with my tripod - timer mode to rule me out - Lets hope I am wrong about my camera and its just Me!!
Thanks for your input
--

Feel free to use any of these additional letters to correct the spelling of words found in the above post: a-e-t-n-d-i-o-s-m-l-u-y-h-c If you find any extra letters, please place them here for future use...
--
Jayboo
 
Due to the semantics of how this has all been posted, I'm still not convinced that I understand exactly what the OP is saying.
Sorry - I'm trying - I really am
When you lock focus by half-pressing the shutter release button, (or better yet, using the AF-On button) the chosen AF point is used to make a measurement of how far to adjust the lens focus. The lens then moves to that position.
Got that
If you do "stutter" on the half-press of the button, the system will focus again on every subsequent "make" of that button contact. So as was suggested, you could be getting a "refocus" accidentally. So it IS a lot better to divorce the AF from the half-press of the shutter button, and instead always use the star button or the AF-On button. That eliminates the possibility of the shutter button causing an unintended refocus.
Don't think I am stuttering - not a problem on 450D
But I'm still not clear what the OP expects. When the manuals talk about the focus staying where you placed it, what they mean is that barring a re-activation of the AF system (a second half-press of the shutter button in this case), the lens simply will not focus again. So the little red rectangle won't move, it won't "track" the eye of the dog, for example.

When you view in a program that shows the selected AF point, the center AF point will always show up in the very center of the frame. It won't somehow track the eye and stay on the eye.
Yes - I realise that - but - what I feel I am getting is loss of focus after re-compose (oh dear - it doesn't sound right - I know what I mean - SORRY)
And in addition, if you focus on the eye, lock focus (don't let the AF motor operate again) and then recompose, you need to realize that the eye may not end up being in good focus after the recomposition. That's because most modern lenses have a flat field of focus. They focus on a plane, not on a sphere.

So, for example, you can shoot a photo of a brick wall, and one focus setting will result in the whole wall being in focus IF you're aimed straight on to the wall.

But we know that the wall near the edges of your photo was farther from the camera than the wall near the center of the photo. So the field of focus is NOT equidistant from the lens. It's a flat plane.

Now, if you focus lock recompose, you're rotating that plane of focus when you move the camera. That means that the eye won't lie in that plane any more. So focus lock recompose is NOT good for critical shots with shallow depth of field.
I see - I think
If you're shooting a portrait at a large aperture (low f/number) you must focus manually after setting the camera position. If you recompose after focusing, you're asking for trouble.
Hmm -


But, in the sample photos posted, it looks like motion blur was the main problem. And keep in mind that if the dog moved, his collar area may have been stationary while his head moved a lot! So that would explain what you're seeing.

You have to eliminate all variables except for the one you're testing for any experiment to be valid.

Shoot at a high shutter speed (at least 1/250th) to keep motion blur to a minimum. Be sure to compare shots taken at the same aperture setting with the same lens. Be sure to compare images at the same size (not at 100%).

Don't expect the red rectangle to track anything. If you recompose after locking focus, the focus point will still show up dead center in the frame because that's the sensor you used when you locked focus.
Yes I know that
Don't be discouraged by rude responses on here, either. Just ignore the posts made by impatient people. Life is too short, you know :)
I have to say - rude or not - YOU ARE ALL EXTREMELY HELPFUL - Thankyou
Try setting C.Fn IV-1 = 3. That removes autofocus from the shutter button. Now, you use the AF-On button for AF. You press the AF-On button, the camera focuses, you take you finger off that button, and the lens stays set where you left it until you press the AF-On button again. I prefer this because I can lock focus with one "aim", lock exposure with a different "aim", and shoot the photo with a third "aim".
I did try this yesterday and it didn't seem to help - but I will try again today - I am going to be printing off some of these responses so I remember all points made
--
Jim H.
Thank you again
--
Jayboo
 
That is absolutely, positively the problem you're having here with getting the eye sharp. 1/15th of a second simply isn't fast enough. Quite frankly, at an f-stop around 7 (is that really what you're shooting this at?) you should have plenty of DOF here. At a reasonable focal length and subject distance (which it looks like you have here) you simply won't see OOF caused by that small a recompose at f7.
To accurately guage what's going on here, you need to shoot a sample with your lens wide open, to make the DOF as narrow as possible, and thus make the focal plane as easy as possible to detect.
OK
  • however - that - maybe because I am THICK - still does not explain to me why the point of focus shifts when I re-compose the shot - unless you are suggesting my hands are extremely unsteady.
I'm a little confused by the problem you're describing here. Perhaps because you're using imprecise language.
Very probably - bad language and camera skills
There is a "focus point" - the red square in your viewfinder that lights up when the camera acquires focus. You've said you're using center-point, which means that this is in the center of your viewfinder.

There is a "focal plane" and a "focal distance" The "focal plane" is the plane parallel to the image sensor, which is exactly the focal distance away from the optical center of the lens.

(It is important to understand that you are dealing with a focal plane, not a focal sphere. This can cause some misunderstanding).

So I'm not sure what you mean by "point of focus."

Here's the problem with focus-recompose at wide apertures.

Let's say you focus on the dog's eye then recompose. The focal plane now moves, because it's a plane, not a sphere. The eye will now be SLIGHTLY in front of the plane of focus.

Now, a couple of months back I actually ran the math on this, and what I found was that, under most practical shooting conditions, even shooting fairly wide (f2.8 ... I may have checked even wider) that the focal plan moved so little during recompose that your image would be acceptably even if you recomposed the maximum possible amount (focusing at the center point, recomposing so that the object you focused on is now in the corner). For a typical recompose, along the lines of what you're doing here, you're simply not doing enough to take the eyes out of focus.
Can I ask you then - when looking at the shot taken on the 50D - this shot is not a huge crop or anything - I was close - if the focus had locked - where it was supposed to - even if Bert (my dog) moved and the eye was out of focus because of that - why the collar area stays sharp - to me it looks like that was where focus locked - oh dear I'm off with my bad language again - sorry
This problem is, however, unavoidable. And if shooting wide open on a very fast lens, it creates some problems. There are really two solutions:

The first is to focus-recompose from the nearest focal point, rather than from center point
Yes - I need to do that
The second - which you'll see a lot of pro's do when focus is absolutely critical and DOF is very, very narrow ... is to focus manually. This is a non issue if you even have six inches of DOF, but slap a 50mm 1.2 lens on your 50D, get close to your subject and open all the way up, and, yeah ... it's an issue.
OK
Again, at f7, however, I simply fail to see how this could possibly be the issue here.
Oh dear!
Thank you - you've confirmed how little I know - bur I'm eager to learn and get it right - I don't want my good photos to only happen by accident.

--
Jayboo
 
At very close focus distanses even f7 is not enough to ensure focus when you do a focus-recompose but then we are talking almost macro shots (I can't see the focal length used in these pictures but it doesn't seem like ultrawide at least, but pretty close to subjrect, no?)
Not wide no - 50mm - and yes - pretty close to subject
It seems the OP is on-top on things but in his shoes I would ensure myself that the lens/camera combo works w/out the recomposition part to start with. If the camera/lens is able to focus correctly on a stationary object (no recompose) then everythings is fine and the only thing needed to be improved is the recompoition technique. The 50D has the lens micro focus adjustment that should be used as well, especially when comparing same lens with another camera body
I'm definately not on top of things - one minute I'm convinced the camera has a problem - next minute I just know its me

I am a little frightened to use the lens micro focus adjustment - not sure I know enough yet - I just may make things worse. Also I did not have the issue I am having now until my camera went to Canon for a repair and I am only using lenses I used before - without issue.

Thanks for your input

--
Jayboo
 
It's interesting to me that we're talking about the same Canon service centre too.

While the Canon HQ is state of the art & environmentally friendly the service centre is the opposite. I could not access the calibration section because their is no wheelchair access at all.

The monitors were all very old CRT's and I had to demonstrate the problem with a technician using a 13" Macbook.
Well today I am going to give it my all and try all suggestions - I'm kind of hoping it is me - what you went through sounds horrendous
thanks again
--
Jayboo
--

 
It's interesting to me that we're talking about the same Canon service centre too.

While the Canon HQ is state of the art & environmentally friendly the service centre is the opposite. I could not access the calibration section because their is no wheelchair access at all.

The monitors were all very old CRT's and I had to demonstrate the problem with a technician using a 13" Macbook.

Wow - that's a surprise - how on earth can they test at all with that sort of equipment - begs the question - do they get tested at all?
Canons range of cameras is very appealing to those like myself who want to get into photography - but surely we should be able to trust that our cameras are operating as they should when we get them - because when you are new to it and get my sort of problem I think only an expert with my camera in their hands could know for sure if its me or it - I have had lots of advice on here - which is all excellent I'm sure - I'm just not sure I'm going to be able to follow it all and even if I do - that the results will be conclusive enough .

Oh well - here goes - wish me luck
--
Jayboo
 
Good luck and I hope you find out that the camera is ok.... or not. At least then you will know.

John
--

Feel free to use any of these additional letters to correct the spelling of words found in the above post: a-e-t-n-d-i-o-s-m-l-u-y-h-c If you find any extra letters, please place them here for future use...
 
Can I ask you then - when looking at the shot taken on the 50D - this shot is not a huge crop or anything - I was close - if the focus had locked - where it was supposed to - even if Bert (my dog) moved and the eye was out of focus because of that - why the collar area stays sharp - to me it looks like that was where focus locked - oh dear I'm off with my bad language again - sorry
Here's the problem.

If the collar is in focus, everything in the same plane as the collar has to be in focus, too.

That's the way it works. So you can't have to collar in focus, and yet the dog's forehead or the back of his nose - one of which MUST be in the same plane as the collar - be out of focus.

This is simply not possible.

The focus locks at a DISTANCE. Everything in the plane parallel to the sensor at that distance from the center of the lens is focused the same.

It seems quite likely to me that your dogs head is moving, but his body is not. At 1/15 of a second it wouldn't take much movement - he had moving slightly as he breathes - to create the problem. This is particularly true on the eye, where it really doesn't look like the problem is focus. Watch your dog when he sits, when he's breathing.

When you do your tests today with cans, make sure to put the cans reasonably far apart, and to use a large aperture (low f-number.) Shoot as wide open as your lens allows you to.
 
Well - didn't really do well today - that awful thing called work got in the way so didn't have much time - weather dark foul and wet - my brain addled so made lots more mistakes.

However I am going to post some shots below and give as much information as I can knowing I got lots of things wrong - but I think I have decided the problem is mostly me - I would appreciate your comments however

1st shot - Tripod - 10 second timer - kit lens 18-200 - 60mm focal length - AV 5.6 - shutter speed 1/125 - really poor light - I don't have flash other than inbuilt which I didn't use - focussed on S - JacobS Creek



2nd shot H/Held AV 3.5 Shutter speed 1/500 - centre focus point - recompose - again using S on bottle



Later in the day - inbetween rain showers - tried again quickly 3rd shot - Tripod Timer Centre focus point around E in Greens - Lens 28-105 shot at AV 3.5 Shutter speed 1/40



4th Example Handheld 50mm lens AV 1.4 Shutter speed 1/800 - focussed on O in Bouillon - recomposed and it stayed put (I am putting this badly I know)



--
Jayboo
 
I think I'm done blaming the camera - I seem to have taken giant steps backwards the last couple of weeks and I'm still not sure why and it has coincided with my camera going off to Canon and its return.

Sorry if I'm whining and wingeing - I have been told I am likely to have moments of frustration in this huge learning cycle but I have taken good shots in the past and not just by accident - the one here I really ws pleased with and I don't feel able to replicate this at the moment



Thanks to all of you for your help and suggestions

--
Jayboo
 

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