40D Sensor Focus Adjust?

Started Apr 25, 2008 | Discussions
flemingljr New Member • Posts: 2
40D Sensor Focus Adjust?

Has anyone figured out how to adjust the 40D's sensor for back focus issues? I can send it in to Canon for calibration, but I'd like to give it a shot before shipping it out.

Keith Reeder Veteran Member • Posts: 3,725
Re: 40D Sensor Focus Adjust?

Assuming you have a problem (I've lost count of the number of 40D "focus problems" that turned out to be pilot error), send it in - adjusting focus isn't a DIY job.

JimH Forum Pro • Posts: 12,912
You can't adjust this yourself.

Keith is right. This is not a DIY job.

AF is adjusted using special software that only the Canon service centers have. You also would require a calibrated "tool lens" which, again, us mere mortals do not have.

This is not a physical adjustment as many believe. Instead, because of the way the AF sensor systems work, (comparing the positions of patterns detected on linear sensor arrays onto which "split images" created by prisms are projected), you don't need to physically adjust anything. You simply tell the camera what positions on which sensor elements should "see" the same pattern positions.

So what happens is that a "lookup table" of data stored in non-volatile memory in the camera gets updated with new data. That is what "calibrates" the body's AF.

DO NOT fall into the trap of attempting any of the "turn this screw" methods that we sometimes see on websites claiming that this will calibrate the camera's AF. They quite simply don't!

Instead, you end up messing up the mirror alignment which then makes it so that the AF cannot be adjusted to be right for all of the AF points at the same time. On the 40D, Canon has taken the wise move of hiding that adjustment so that we won't be tempted to fiddle with it

If you really do find that you have an AF problem, send or take it to a canon service center.

And be very sure that your testing methodology is sound before coming to the conclusion that you do have an AF problem. There are a LOT of websites and posts telling us how to test AF, and a lot of them give very bad advice which can easily result in "false positives". So a lot of people probably end up sending perfectly good cameras away to be calibrated by Canon.

Then again, AF calibration adjustment can be needed. I'm just saying that you should take the time to test properly before wasting your time sending the camera away.

-- hide signature --

Jim H.

Keith Reeder Veteran Member • Posts: 3,725
Re: You can't adjust this yourself.

Excellent - and comprehensive - advice, Jim.

Bohdan Senior Member • Posts: 1,122
I would have to assume

that this type of calibration must be done on the assembly line which begs the question, how could they get it wrong ?

If one explains it away buy shipping damage etc... then the camera seems to be a little flimsy, or poorly assembled in certain cases.

-- hide signature --

I may be, and probably am, completely wrong.

grey_squirrel New Member • Posts: 16
Re: 40D Sensor Focus Adjust?

I would agree, just send the camera to Canon. After a few months of using my 40D I realised the pictures from my old 300D were sharper. I sent the camera (and a few lenses) to canon for calibration and the difference is really noticeable (now much better). They also changed a few parts of the focusing system of one lens free of charge even though i had not asked for anything and it was 3+ years old.

I have to admit that I am now very satisfied with Canon's service even though i wished the focusing on the 40D was right from the start. I would not hesitate to send your Camera if you can part from it for more than 1 week:-)

Torch Senior Member • Posts: 1,979
Re: You can't adjust this yourself.

So basically your saying Canon does not have time to apply a calibrated lens tool properly at the factory 100% of the time. Those who want to be assured the product they bought is at its best focsing requires they send it in for service.

I don't mind doing a calibration routine myself, but I am not interested in sending anything in that doesn't have a scratch unless it's a recall notice and even then I may reconsider if there is no problem.

JimH wrote:

Keith is right. This is not a DIY job.

AF is adjusted using special software that only the Canon service
centers have. You also would require a calibrated "tool lens" which,
again, us mere mortals do not have.

This is not a physical adjustment as many believe. Instead, because
of the way the AF sensor systems work, (comparing the positions of
patterns detected on linear sensor arrays onto which "split images"
created by prisms are projected), you don't need to physically adjust
anything. You simply tell the camera what positions on which sensor
elements should "see" the same pattern positions.

So what happens is that a "lookup table" of data stored in
non-volatile memory in the camera gets updated with new data. That
is what "calibrates" the body's AF.

DO NOT fall into the trap of attempting any of the "turn this screw"
methods that we sometimes see on websites claiming that this will
calibrate the camera's AF. They quite simply don't!

Instead, you end up messing up the mirror alignment which then makes
it so that the AF cannot be adjusted to be right for all of the AF
points at the same time. On the 40D, Canon has taken the wise move
of hiding that adjustment so that we won't be tempted to fiddle with
it

If you really do find that you have an AF problem, send or take it to
a canon service center.

And be very sure that your testing methodology is sound before coming
to the conclusion that you do have an AF problem. There are a LOT of
websites and posts telling us how to test AF, and a lot of them give
very bad advice which can easily result in "false positives". So a
lot of people probably end up sending perfectly good cameras away to
be calibrated by Canon.

Then again, AF calibration adjustment can be needed. I'm just saying
that you should take the time to test properly before wasting your
time sending the camera away.

-- hide signature --

Torch

JimH Forum Pro • Posts: 12,912
Re: I would have to assume

That is always the question, really.

Why do we sometimes end up reading about cameras whose AF requires adjustment right out of the box?

I would guess that this actually happens less often than we might imagine from reading on this forum. People do get "bad out of the box" bodies, for sure. But as is often pointed out: Most of us do not come on here and make a post to tell everyone that our AF is working fine. Yet if it appears that it isn't working fine, we're very quick to post here to ask about it.

Often, I think people trust the advice of various websites and other posters about how to perform AF testing. And this advice is frequently wrong. Those badly-designed AF tests, then, lead to a lot of "false positives" where people believe that their AF is not working, when in fact, it is well within the rated specifications.

So two things are at work:

1. We read only about AF problems, not AF success stories.

2. A lot of people, perhaps lead into paranoia from reading on here, believe they may have AF problems when it's really just operator error or unrealistic expectations. Then they use faulty testing methods and "prove" that they do have "problems".

I'm not saying that people never have AF adjustment issues. I am very sure that they do. But the actual problem rate is probably a lot lower than one might think based on what one reads here.

As far as how they could get it wrong at the factory: Beats me! I would hope that this is checked carefully before a camera is shipped out. One does wonder if things mechanically shift in transport at times, or if there are problems in the design of the calibration process employed at the factory that leads to some bad calibration.

I would imagine, though, that Canon and the other manufacturers try to set up their designs and calibration procedures to minimize these problems. It must be quite expensive for Canon USA Service to adjust bad bodies or lenses for free later. It's much cheaper to get it right to begin with, at the factory, where they're set up to do it with no receiving, handling, and then re-shipping costs. So we'd imagine that they DO try to be very careful. But I'm sure that there are tradeoffs. I'm just not sure what the balance is.

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Jim H.

JimH Forum Pro • Posts: 12,912
Re: You can't adjust this yourself.

Torch wrote:

So basically your saying Canon does not have time to apply a
calibrated lens tool properly at the factory 100% of the time. Those
who want to be assured the product they bought is at its best focsing
requires they send it in for service.

I'm not sure I'd go that far.

I suspect that Canon tries very hard to get it right at the factory. And I suspect that the vast majority of the time, they get it right and the customer gets a very well calibrated body right out of the box.

But we do read about the occasional "dud". Whether that's from shipping damage (which might imply some lack of robustness in the camera itself) or if it's from a faulty calibration at the factory, we'll never really know, I guess.

I would hope that the actual "bad right out of the box" rate is very low. We just read more about the bad ones than we do about the good ones on here.

I don't think we need to send every camera in for calibration by any means. One gets that impression on here at times, but I don't think it's nearly that bad. I've got two Canon DSLR bodies and many lenses. I have yet to ever find the AF on any of these items to be "off". To the contrary, I'm amazed at how well it all works. My experience is likely to be fairly common, I'd think.

I don't mind doing a calibration routine myself, but I am not
interested in sending anything in that doesn't have a scratch unless
it's a recall notice and even then I may reconsider if there is no
problem.

I think the problem is that since we don't have access to calibrated references (the so-called "tool lenses", etc.) and we do not have a proper, standardized AF test bench and range either, if Canon let us do our own AF adjustments, they'd end up with a LOT of badly and improperly calibrated bodies and lenses out there. And ultimately, since things get sold used, swapped, traded, loaned, etc., Canon might end up with a really bad name if you couldn't trust the AF calibration of anything because ill-equipped end-users were out there messing things up right and left.

So Canon keeps their AF calibration software proprietary.

I really do think that based on a LOT of the posts here where people are not even testing their AF properly, the chances that they'd be able to adjust it properly on their own is frighteningly low.

But having said that, I'd love to have the cal software myself

What they could do would be to have the "user version" of the cal software set a flag of some sort that tells other people that the body or lens has been "user calibrated". And it'd be great if the "user calibration" could always be "rolled back" to the previous factory calibration. That'd give us the ability to do it ourselves yet give us or a future buyer the ability to set the body or lens back to the last Canon calibration settings.

That way, we'd have the fun and utility of being able to do it ourselves but we'd have none of the downside of our "home brew" calibration messing things up (and thus requiring a Canon calibration to correct it).

-- hide signature --

Jim H.

MarcosV Veteran Member • Posts: 6,372
Re: I would have to assume

Bohdan wrote:

that this type of calibration must be done on the assembly line which
begs the question, how could they get it wrong ?

It costs lots of money to ensure 100% of the cameras are at the best calibration possible.

I remember how things were with NTSC TV sets --- the difference between some of Sony's pro-sumer grade sets and their high end pro sets were the amount of additional tests that were performed on the higher end sets.

I expect Canon to tune their final integration and test procedures to have a high percentage of cameras be properly calibrated, but, not 100%. They probably do take a good look at how many cameras goes to their repair centers for AF calibration and factor that along with sales into the equation.

If one explains it away buy shipping damage etc... then the camera
seems to be a little flimsy, or poorly assembled in certain cases.

High performance equipment typically have even higher maintenance costs because it can take lots of additional money to keep things calibrated to those higher standards.

In the aerospace business, we pay orders of magnitude higher prices to have parts with that 99.99999999999% in spec performance and reliability. Aside from additional testing, the manufacturing costs go up along with the rejection rates. I honestly don't expect consumer grade gear to always be in spec out of the box or keep calibration over time with heavy use.

What's more interesting is what's the average for the industry: is Canon really doing a worse job than Nikon or Sony when it comes to AF performing to manufacturer's specs? How long does the gear stay in calibration?

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Bohdan Senior Member • Posts: 1,122
Of all camera owners

only a tiny amount post on boards such as this. The majority do not.

One would think that frequent visitors here are more "enthusiasts" and more apt to wonder whether their equipment is working within spec.

What I am getting at is that the majority of DSLR buyers would be more prone to accept user error for their poor performance and not even think that their equipment might be faulty.

I have a few friends with very expensive body and lens setups that take less than 500 shots a year. They would not even dream that a defective body or lens is even possible.

I'm sure there are lots of unreported problems out there.

-- hide signature --

I may be, and probably am, completely wrong.

JimH Forum Pro • Posts: 12,912
That's a good point too.

The very fact that someone is posting to a forum like this shows that they may be more of an "enthusiast" than most. So they may tend to be more critical of things and expect more.

I suspect that a lot of defects are out there, but go undiscovered simply because the owner has no frame of reference. So they figure it's just their own fault.

So it goes both ways.

Still, I suspect that we get a skewed idea of the percentage of defective items when we read a forum such as this. And that's normal because people ask when they've got problems, not when things are working well.

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Jim H.

JimH Forum Pro • Posts: 12,912
Excellent points. (NT)
-- hide signature --

Jim H.

Keith Reeder Veteran Member • Posts: 3,725
Re: Of all camera owners

Bohdan wrote:

I'm sure there are lots of unreported problems out there.

And - obviously - lots of unreported perfectly-functioning cameras too.

GaborSch Veteran Member • Posts: 7,203
Canon's way of QA

Torch wrote:

So basically your saying Canon does not have time to apply a
calibrated lens tool properly at the factory 100% of the time

I think Canon adopted the typical North American quality assurance: let the customers do that.

See http://forums.dpreview.com/forums/read.asp?forum=1019&message=27447553

One would think adjusting the cameras or lenses via repair is more expensive than testing each copy at the factory. This is not so, because

1. the customers are not paid for the test,

2. the dealers are not paid for the associated costs (if the customer brings back the faulty equipment),

3. most importantly: probably the wast majority of failures remain unnoticed or unrepaired (because the customer does not recognize the problem, or he attributes it incorrectly, of he does not want to part from his gear for weeks).

Bohdan Senior Member • Posts: 1,122
That' not the point....

how many in spec camera and lenses out there is small comfort if the odds are more than insignificant that you may not be as lucky.

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I may be, and probably am, completely wrong.

vladm
vladm Forum Member • Posts: 51
Re: 40D Sensor Focus Adjust?

grey_squirrel wrote:

I would agree, just send the camera to Canon. After a few months of
using my 40D I realised the pictures from my old 300D were sharper.
I sent the camera (and a few lenses) to canon for calibration and the
difference is really noticeable (now much better). They also changed
a few parts of the focusing system of one lens free of charge even
though i had not asked for anything and it was 3+ years old.
I have to admit that I am now very satisfied with Canon's service
even though i wished the focusing on the 40D was right from the
start. I would not hesitate to send your Camera if you can part from
it for more than 1 week:-)

not the same here:

I sent my 40d to NJ Canon along with lenses in the separate shipments (they requested them to be shipped separately). Everything came back last week (again, separately) with the notes on both lenses "Send with the body"... So they simply didn't see that body there as well. And this is after I talked to 2 people on the phone and they confirmed - "yes, techs will see your body and calibrate one to another and that it's recorded in their internal system."

I'm going to call them

-- hide signature --

Vlad

Wayne Larmon Forum Pro • Posts: 10,634
What is the proper method of testing AF accuracy

JimH wrote:

And be very sure that your testing methodology is sound before coming
to the conclusion that you do have an AF problem. There are a LOT of
websites and posts telling us how to test AF, and a lot of them give
very bad advice which can easily result in "false positives". So a
lot of people probably end up sending perfectly good cameras away to
be calibrated by Canon.

What is the proper method of testing AF accuracy?

Wayne

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