20D focus problems AGAIN!

[Astbury]

Found this on another Forum: http://forum.pbase.com/viewtopic.php?p=69137

Looks like the 20D does have a focus issue and that the sensor is not where we think it is!

C

[tim]

Like I said the last time this came up, I have two 20D's and a bunch of lenses, and my camera focuses correctly 99% of the time. Use the centre focus point and be careful with your technique and the 20D will do well for you.

[Mark_Cohran]

I've been using my 20D for 14 months now and have had no problems with focus. I generally manually select my focus point, and I find the camera works great.

Mark

[Starman]

I heard that about 10-15% of the 20d's have a slight focus issue, and that you can send it to Canon for free calibration.

[Mark_Cohran]

I heard that about 10-15% of the 20d's have a slight focus issue, and that you can send it to Canon for free calibration.

Can you provide a source for the 10-15% number? I've never heard or read that anywhere. In my experience, most of the time these issues get way overblown by 1-2% of people who simply don't know how to use their camera. That's not to say there aren't some bad copies out there, but 10-15%? I seriously doubt the validity of those numbers.

Mark

[Starman]

Yeah, I'll Check around online, but that's what one of my teachers told me.

[Curtis N]

Yeah, I'll Check around online, but that's what one of my teachers told me.I once had a teacher tell me that if I travelled westward, as soon as I crossed the international dateline I was going east.

Keep your salt shaker handy, you may need a few grains.

[liza]

Can you provide a source for the 10-15% number? I've never heard or read that anywhere. In my experience, most of the time these issues get way overblown by 1-2% of people who simply don't know how to use their camera. That's not to say there aren't some bad copies out there, but 10-15%? I seriously doubt the validity of those numbers.

Mark

I agree with Mark. It's usually inexperienced users who have these issues. DSLR's have a bit of a learning curve, and it takes time to become accustomed to them. Time and patience is the key.

[Tom W]

I once had a teacher tell me that if I travelled westward, as soon as I crossed the international dateline I was going east.


Of course you will - until you fall off the edge of the earth! :)

[Tom W]

I agree with Mark. It's usually inexperienced users who have these issues. DSLR's have a bit of a learning curve, and it takes time to become accustomed to them. Time and patience is the key.

Speaking of which, Canon should really do better at describing the kinds of issues that occur when shooting with something larger than a point-and-shoot. Depth-of-field, ISO, shutter, aperture - a little primer book would do wonders in preventing a lot of the problems that new DSLR (and film SLR shooters for that matter) have if they haven't experienced this type of camera in the past.

[Doom1701e]

I am very experienced with the 10D and now the 20D and have had focus issues for the last 6-8 months. I have had my 20D since its first week of release in 2004 and it worked fine for a while, but now 30-50% of shots I take are backfocused. I dont have the time right now to ship all my stuff to Canon for calibration so I guess I will just have to buy a new 1DsMII :). No 1Ds for me, but hopfully a 25D or 30D later this year. I just wish there was a local authorized Canon repair center near the bay area so I could get this thing calibrated or something.

[ronosmena]

I agree with Liza, I have had mine for over a 7 months now, and I am still learning alot from it. Rome wasnt built in a day, so I guess patience is always a virtue.... Just IMHO

[GSH]

I occasionally have focus problems with my 20D too.

I don't need to search on forums to know there's a problem, although i can guarantee 100% of my focus issues are because i'm a cack-handed so&so :D

Can i send myself in to Canon for Calibration ? :confused:

[steved110]

This is probably a stupid question, I'm a brand new DSLR user - just checked the search facility but the topic doesn't come up as a separate issue. What exactly is back focus? I get the impression it means the camera focuses behid the subject you want?
How can you tell if you have it?
TIA,
Steve

[Jaymz]

How much front/back focusing is acceptable? I tested my 20D today and using a ruler, center AF point centered on the 8" mark, the sharpest spot is almost at the 9" mark. I have never noticed any problems, was just curious to see how far off it is.

[Tom W]

How much front/back focusing is acceptable? I tested my 20D today and using a ruler, center AF point centered on the 8" mark, the sharpest spot is almost at the 9" mark. I have never noticed any problems, was just curious to see how far off it is.

Focus testers beware - simply laying out a slanted ruler will not give an accurate indication of a camera and/or lens' focusing accuracy. Why? Because the AF sensors are not the same size as the indicators on the camera. Here's an image I "borrowed" from a post by Chuck Westfall of Canon a while back that shows the 10D's focus indicator squares vs. the actual sensors overlaid in red (the 20D and 5D have similar dimensions relative to their sensor indicators):

http://www.pbase.com/photosbytom/image/42250385.jpg

Imagine laying your ruler diagonally across that center point. The AF sensor can pick up on any high-contrast line within the coverage area of the AF sensor.

This site has a more acceptable means of testing focus:

http://md.co.za/d70/chart.html

Even though the site is aimed towards the Nikon D70, the premise is valid. The AF technology is very similar.

[Jaymz]

Thank you Tom, that makes alot of sense.

[Tom W]

I did a little demonstrative pixel-peeping and came up with this crude overlaid image of a ruler (sorry, the slide rule was all I could find) and the 10D focus point diagram. This is what I came up with:

http://www.pbase.com/photosbytom/image/54816785.jpg

As you can see, the AF cross in the center could easily latch on to any of the contrasty hash marks on the ruler that fall under it's sensor. This is why having either a perpendicular surface or a very thin, bold single line is essential. I prefer the perpendicular surface myself.

[Jaymz]

I spent a few hours last night experimenting with the focusing and I determined I wasted my time. :) There is nothing wrong with it, just as I figured, but I did learn alot about the focusing system, so it wasn't a total loss. Thanks again Tom for the info.

[Jon]

Found this on another Forum: http://forum.pbase.com/viewtopic.php?p=69137

Looks like the 20D does have a focus issue and that the sensor is not where we think it is!

C
That's not exactly news. I've said before on here what anyone can see on looking at the camera's mirror box. The AF sensors are on the bottom of the mirror box, not behind the focussing screen. The marks on the screen will, if the screen's perfectly in alignment, line up with the spots that are used for AF, but they aren't the exact spots that are.

[DavidEB]

TomW -- never apologize for a slide rule. As a wise man once said, "an elegant weapon for a more civilized age"

[mcs550]

Tom W. Excellent work and advice. Will we see that slide rule on antiques roadshow?

[Tom W]

TomW -- never apologize for a slide rule. As a wise man once said, "an elegant weapon for a more civilized age"

On the other hand, it makes a horrible linear measuring tool. And it's not that good for lens testing either. How do you tell Canon that your lens is backfocusing by Pi?

[Jon]

On the other hand, it makes a horrible linear measuring tool. And it's not that good for lens testing either. How do you tell Canon that your lens is backfocusing by Pi?
Just complain about the spherical aberration. I've got one of those guys upstairs, and another right here next to the computers along with my trusty hex and decimal abaci.

[Tom W]

Just complain about the spherical aberration. I've got one of those guys upstairs, and another right here next to the computers along with my trusty hex and decimal abaci.

You've got a hex abacus? Wow!!

[Gary Petersen]

Of course you will - until you fall off the edge of the earth! :)

And if you miss the elephants you can land on the back of the turtle.:lol:

[minime9us]

I wish i could rule out that i have a focusing problem before i send my XT to canon. I went to 2 camera shops and after they shot with it and then shot with their XT and compared the photos they both said "If i were you id send it back its not as sharp as it should be." I had the 50mm 1.8 on my XT and the stores XT was using the kit lens and the kit was sharper than my 50mm. Can someone explain this?

[malla1962]

I was quite happy with the focus on mine most of the time,if there was ever a problem I just put it down to me,But I have heard a lot of people complain about the problem on the 20D and the 10D.

[Astbury]

Im finding that the close up focus is not an issue, i mean with the slide rule or the focus test paper all the time showing that the camera is working just as it would be expected to do.
I see my problems in shots that are further away, so this leaves me thinking back to the problem still might be user error, camera shake. I did the pencil test as mentioned by someone else and had perfect focus every time, with the kit lens, a borrowed Canon L lens and my EF lenses.

Going out later today to see how I can do again, the weather is a little brighter too.

Cheers

C

[tough_dog]

My 20D with 17-85mm lens had a consistent front-focus error when the kit arrived last August. I did extensive testing, including use of the Nikon D70 focus chart cited by Tom W. The most obvious test to me was placing three upright AA penlight cells on a diagonal about an inch apart with the left and right cells each about half-inch closer or further than the middle cell. Using single-shot with center-sensor autofocus, the center sensor was focused on the middle penlight cell at a distance of about 20 inches with the lens wide-open at 85mm so that the left and right cells were near the sides of the frame. The result of many trial shots was consistently sharp focus on the closer left cell with progressive defocus on the middle and right cells. Reversing the left-right front-rear cells still retained sharper focus on the front (now right) cell. Anyway, I went to the Canon website and filled out an online form (with serial numbers) indicating I was sending both the camera and the lens in for calibration. Mailed them away to Irvine, CA and got them back in about two weeks. Canon even emailed a shipping notice once they were in-transit back. Both now focus perfectly. So, it is possible to have a front- or back-focus problem which is not operator error. It is also possible to get it fixed (calibrated) while under the year warranty for just the cost of one-way postage (with insurance and receipt confirmation) to Irvine or other repair center.

[Tom W]

.... So, it is possible to have a front- or back-focus problem which is not operator error. It is also possible to get it fixed (calibrated) while under the year warranty for just the cost of one-way postage (with insurance and receipt confirmation) to Irvine or other repair center.

Indeed it is, and if it occurs, it should be adjusted. I hope I didn't give the impression that it doesn't occur. I did, however, want to point out that people often test improperly. I hate to see something get sent in for no reason other than a poorly-performed test. It's always good to overtest and question one's own procedures to be sure.

[Jraun]

Great question Steved110 - post it as a new string - woud like to know the answer?

[rufis6]

I had a 20D an also experienced "soft focus" problems. The usual suggestion was that I use the USM filter in Photoshop. That is obviously not the answer; you can't sharpen what ain't there. If the picture is out of focus all the sharpening in the world is not going to help. I have since bought the 5D and now I am a happy camper.