Jump to content

10D Focus Issue - Repair or Replace?


Recommended Posts

I've had my 10D since July of 2004. It's never been razor sharp like I'd like,

but lately it seems worse. After some searching I found Bob's article on doing

a focus test and tried it out.

 

I got as close to 40* to the target as possible and used my Sigma 28-70 2.8 EX

lens for the test tripod mounted. It seems my 10D is front focusing when I use

auto focus.

 

I called Canon and they want me to send it in. They had no idea what the

estimate for repair would be until they get the camera body.

 

Does anyone have experience with this? I've been eyeballing a 40D but I'd like

to have this 10D operational as a backup.

 

Advice is appreciated.

 

-J<div>00NWpi-40177584.jpg.d559afd140aac18a674fa9bce0f4cf8b.jpg</div>

Link to comment
Share on other sites

Do all your lenses front focus? If not then it's not likely to be the body that has the problem.

 

The trouble with using a Sigma lens on a Canon body is that Canon won't touch the lens and I'm not sure I'd trust sending the body and lens to Sigma, since if they adjust the body, you may have focus trouble with your Canon lenses.

Link to comment
Share on other sites

I had the same problem with my 20D, after much fluffing around I decided on another test to see

<UL>

<LI>which focusing points were out

<LI>by how much

<LI>giving the subject a more distinct focusing item

</UL>

<P>

I put minor marks on the paper (with the paper secured on the table at an angle to the camera) and then held my pencil over each mark <b>clearly in the focusing point I had selected</b>. This allowed me to test if each focusing point was accurate and (I hope) ensure in the test that the <b>physical focus sensor</b> was over <>the indicated focus point</b><div>00NWsc-40178084.jpg.1b6472da11bbab8662e7f4c3a25e356d.jpg</div>

Link to comment
Share on other sites

I don't know if your 10D had actual problem, or due to user error. However, do yourself a favour and avoid any 45 degree tests like these as they are flaw by design. The idea might appear to be sounded but not so when you understand how the DSLRs are actually assembled.
Link to comment
Share on other sites

Allan

<P>

sounds interesting, so I'd be keen to understand your descriptions of just how they're flawed. I'm an electronics engineer, so don't be afraid to use some technical descriptions.

<P>

I photograph in the real 3 dimensional world (as I do not do copy stand work) and so focusing on a point (such as my pencil tip) should replicate the world as I see it. The presence of a tilted background assists in the observation of just where the focal plane is ending up.

<P>

of course a picket fence or markers along a wall would be another indicator, but would still result in an inclined plane.

<P>

J. Orrand ... on these focus errors

<P>

<UL>

<LI>DoF is typically shallow, especially at the close end of the focus scale, its uncertain how accurate AF is at these distances.

<LI>AF on these cameras is not (by design) intended to be perfect. I can't recall the standard error that is allowable.

<LI>stopping down to more common working apertures (like those that <B>P</B> would choose) may indeed render the subject within the DoF, thus work within the programs accepted tolerances

<LI>AF points may not actually <B>be</B> precisely where the focus point is marked on the viewfinder

<LI>USM lenses stop when they're told to by the camera faster, thus resulting in less overshoot, this can result in more accurate focus. Have you tried release and repress to discerne if the camera subtly adjusts focus again? Some lenses result in a little too-ing and fro-ing before settling on one point.

</UL>

<P>

HTH :-)

Link to comment
Share on other sites

Hi Chris. I use Pentax but the basic ideas should be the same. Not long ago I was calibrating my own camera and these are what I discovered. As you have already known some of them, the actual AF sensor might not be aligned perfectly to the exact centre. But what's more is each tiny AF sensor actually covers certain area instead of a point. What this means is that anything falls within this area could be "picked" by the camera. Exactly how large each AF sensor is model dependent and many end users don't have a clue (and the focus screen indicators are by no mean to represent the actual coverage). One interesting thing that I have discovered is that for typical indoor environment when the EV is much lower than daylight environment, the AF accuracy drops. This only gets worse when trying to obtain precise and repeatable AF confirmation at close-up distance. I could test it all day and they are different everytime. But as soon as I mount a standard or tele lens on the camera and test it in daylight environment near infinity, the AF accuracy would be repeatable. Somebody with more insight could probably explain these but what I have found is that those ruler, newspaper, 45 degree chart or whatever similar ideas, I tried them all but none was useful for actually camera AF calibration. Not sure how many people are aware of this, but cameras and lenses are calibrated based on some virtual infinity targets then let everything else falls into place, not the other way round by testing on closeup targets like most people do on the internet. But those "angled" targets are particular worse because you have no idea what the camera actually sees and thinks.
Link to comment
Share on other sites

Allan

<P>

 

good points that you raise, seems we're on the same wavelength (within a

few Hz at least;-) We seem to have expressed some common findings:

 

<i>This only gets worse when trying to obtain <U>precise and repeatable</U> AF

confirmation <U>at close-up distance</U>. I could test it all day and they are

different everytime. But as soon as I mount a standard or tele lens on the

camera and test it in daylight environment <U>near infinity</U>, the AF accuracy

would be repeatable</i> [added emphasis mine]

 

<P>

 

you say: <I>One interesting thing that I have discovered is that for typical indoor

environment when the EV is much lower than daylight environment, the AF

accuracy drops.</I>

<P>

This is perhaps explained by the construction of AF sensors which combine both

vertical and horizontal sensors on the same site. I think that for Canon

this is only the center sensor. There is also different sensors for f2.8

lenses as well as lower f stop lenses. I understand that this is not with

all cameras (and know nothing much about how Pentax operates)

<P>

 

you say:<i>But those "angled" targets are particular worse because you

have no idea what the camera actually sees and thinks.</i>

 

<P>

 

I agree, which is why I chose to use the pencil (which is raised somewhat)

above the page. This way I could see if the sensor was capturing the

pencil or the paper behind it. As you'll notice from my image, it was well

focused on the pencil. However the most significant finding from this (as I see it)

towards a properly constructed test it to ensure that when testing, you know what

your focusing point is actually covering. As I understand it, your major criticism

of the 'tilted test pattern' shot is that <U>the coverage of the actual focus point

needs to be verified</U>. Until this is known, it could be that the focus is perhaps

on the paper surface, not on the line which is expected.

 

<P>

 

I started my testing because I found that some of my images were not

focused where I was sure I'd put my focus point (and which the software

confirmed I had). And after reading adopted my modified version of the

tests I found, for all the reasons stated here.

 

<P>

So, I think we're on to a good path here. Perhaps a more formalised and

'repeatable' test might be done to determine if a camera has a problem.

<BR>

to summarise this test:

<UL>

<LI>identify exactly where the sensor is in the view finder (it might not be under the maker)

<LI>test with the lens being focused from infinity and from minimum focus to determine if back focus or fore forcus is influenced by the electro mechanics of this operation

<LI>perhaps <I>multiple focus</I> the point (press and release a few times till no further changes are occuing in focus)

<LI>the test requires a method of determining the focal plane (consideration needs to be given to the design of the lens, is it curved field or flat field)

<LI>camera, focusing target, and focus determination point need to be fixed.

</UL>

<P>

please follow up with any additions I might have missed

<P>

So, to J Orrand, hopefully this means that you can perhaps delay spending money

on your camera. Perhaps test it again as outlined in either this test, or my previous more simple test

and see if your camera is still playing up. FWIW I found that focus error was worse on my 18-55 lens.

This has <I>dreadful</I> play in it (try touching the outside focusing ring when focusing

manually and feel / see how much the image moves.

<B>Precision is not part of this system</B>.

 

<P>

 

hopefully what has been said here now will assist others in future, that is if anyone ever searches here.

<P>

Lastly, thanks Allan for making me think harder about my initial testing.

<P>

:-)

Link to comment
Share on other sites

Thanks to all for the added insight. I've been saving change from the couch cushions to buy some good Canon L glass, but for now this Sigma was the best I had. I'll borrow a friend's Canon 50mm 1.8 and test this again and post back my findings.

 

I do hope it's just the lens as I'm planning to upgrade to a Canon 24-105 L soon.

Link to comment
Share on other sites

When you were doing your focussing tests -- I presume you were using "one shot" focussing. The question I have is were you just focussing once?

Sounds strange but I found the following when I used a 10D and the Canon 24-70L

Focussing once often gave a missed focus shot. -- Usually to the other side from where the focus was originally. -- ie If the lens was on infinity and I focussed on an object at 3m, it would front focus, and if it was on say 1m, and I focussed on an object at 10m it would back focus.

Basically the camera/lens combination was overshooting initially and not coming back.

I got into the habit of double or even treble focussing, and that cured the problem -- razor sharp every time. I don't have the same problem with the lens on my 1DMk2 or 1DMk3 so I guess it was a camera fault which I never bothered to get "repaired"

 

Hope this helps -- Steven

Link to comment
Share on other sites

When you were doing your focussing tests -- I presume you were using "one shot" focussing. The question I have is were you just focussing once? Sounds strange but I found the following when I used a 10D and the Canon 24-70L Focussing once often gave a missed focus shot. -- Usually to the other side from where the focus was originally. -- ie If the lens was on infinity and I focussed on an object at 3m, it would front focus, and if it was on say 1m, and I focussed on an object at 10m it would back focus. Basically the camera/lens combination was overshooting initially and not coming back. I got into the habit of double or even treble focussing, and that cured the problem -- razor sharp every time. I don't have the same problem with the lens on my 1DMk2 or 1DMk3 so I guess it was a camera fault which I never bothered to get "repaired"

 

Hope this helps -- Steven

 

I was focusing 2 or three times until I didn't hear any more movement from the focusing motor.

 

I'll post an update tomorrow after I test with a true Canon lens.

Link to comment
Share on other sites

Steven,

 

I was just talking about that in a different thread! Here is a partial copy of my post:

 

---

By reading recent posts on this forum, I have found a very interesting link (Technical overview of Canon AF): (link)

 

The infos found at that page could explain some of my focus issues. As you noted, I was using a small aperture. This combined with the fact that the AF is calibrated for a circle of confusion of 0.02mm may explain that focus stops way short. On a 10mp APS-C censor, 0.02mm is 3.45 pixel wide (3888*0.02/(36/1.6)). This is a large number! If AF is satisfied with a 0.02 circle of confusion, the resulting photo will have pixels blurred on a width of 3.45 pixels (defect clearly visible at 1:1 resolution).

 

I have found a way to prove/disprove indirectly this theory. If the AF stops as soon as it finds a 0.02mm circle of confusion, the prior lens focus distance will have a measurable effect on the focus plan distance. A simple experiment just shows that:

 

- Set manually the focus distance to the minimum. Aim to an object at say 3m. Turn AF-ON. Note the focus distance.

 

- Set manually the focus distance to infinity. Aim to same object. Turn AF-ON. The focus distance is now noticeably longer. Try this at home it is interesting!

---

 

Based on the that, I think it is safe to say that prior focusing distance does have an effect on how AF will work next. This could also explain the difficulty to reproduce AF calibration tests.

 

Antoine

Link to comment
Share on other sites

Antoine

Thanks for the reply:-

I don't know the figures, but presumably the acceptable circle of confusion would be significantly smaller for the 1 Series cameras which would explain why I had the "problem" with the 24-70 on my old 10D, but haven't had anything using the same lens on my 1D2 and 1D3.

You noted a difficulty in reproducing AF calibration tests. Presumably now with the 1D3 the camera's acceptable circle of confusion is sufficiently small to negate the prior focusing distance effect and make it worthwhile putting the ability to calibrate individual lenses into the camera for the user as they have?

- Steven

Link to comment
Share on other sites

I re-tested my 10D using a Canon 50mm 1.8 lens. The results were MUCH better showing that my problem is in fact the lens and not the 10D. Thanks to all that helped me out and saved me from sending my camera in un-necessarily.

 

Now the question is what to do about the lens. I'm going to check with Sigma to see what they say.

 

Here's an update shot from the 10D with Canon 50mm 1.8<div>00NYCK-40207284.jpg.60c028887e2a268467a3866ad26b66c0.jpg</div>

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...