Canon 70-200 F/4 L lens focusing problem with 20D

[jose_marin]

Hi everyone,

 

I just received my Canon 70-200mm F/4.0 L lens and shot some pictures

at standard objects around the house at a distance of about 10 feet

and I'm having a major problem. The focus point is not sharp, but a

little bit in front is. An example is that I took a picture of a

doll my wife has and I aimed to focus on the eyes. The nose seems to

be sharp and the eyes came out soft. I then took pictures of a

picture on the wall the lines come out soft. Am I having a problem

with the lens. I have a Tamron 28-75mm XR Di and this does not

happen at all. By the way, I have also tried taking the pictures

with my tripod, just to eliminate handeheld shots. Most shots by the

way were taken at the 70 mm and 200 mm magnifications. I'm

stomped...please help...JD

[andrew robertson]

DOF extends 1/3 of the way in front of the focus point, and 2/3 of the way behind, so I

think you are just fooling yourself into thinking you have focus issues.

 

Ansel Adams 'The Camera' describes this in great detail. You probably don't see it with

the Tamron because of the greater DOF.

[bobatkins]

<em>DOF extends 1/3 of the way in front of the focus point, and 2/3 of the way behind</em>

<p>

Common myth, and like most myths, it's wrong.

 

<p>

See <a href="http://www.photo.net/learn/focustest/">Focus Testing</a>

[andrew robertson]

Referring to page 50 from Adams' 'The Camera' -

 

"You will note that from examining such a scale (he is referring to the DOF scale on a lens)

that the near limit of depth of field is always a shorter distance in front of the primary

focus plane than the far limit is behind it. This fact leads to a common rule of thumb for

depth of field: For many situations, you should focus about one third of the way from the

nearest object that must be sharp to the farthest."

 

There are many other corroborations in the literature of this fact, but it is easiest if you

simply try it out yourself.

[jose_marin]

Gentlemen, I'm a little confused. If I point the red focus point on the subject's eyes, shouldn't this be the sharpes point in the picture with 1/3 in front and 2/3 in back acceptably sharp? I would think that wherever I point the focus point would be the sharpest. This is true of the Tamron and the kit lens that came with the camera. Any comments on this...

[aleksandar_kujucev1]

My 10D had front focusing problem and I replaced it.

 

My new 1DsMkII had this problem also, but not with all lenses. Also the problem was different on each lens.

 

When I went to the service, I was told that this actually is a camera/lens combination thing and that it is unique for each lens.

 

I took all seven of my lenses and they calibrated the camera for the correct "AF stop point" of each lens (which due to the age, or manufacturing variations is unique for every sample).

 

They are perfect now!

[davef]

"I took all seven of my lenses and they calibrated the camera for the correct "AF stop point" of each lens (which due to the age, or manufacturing variations is unique for every sample)."

 

Where did you take your equipment? Directly to a Canon service facility? How long did it take to get your equipment back? Thanks.

[carlos_santos2]

Sheez! Have you guys had the same experience with this?

 

Sent my (now out of warranty) DRebel in with a newer 85mm f/1.8 which was misaligning the focus point on the out-of-warranty body but not on another dRebel body (to the point where it was pretty annoying, about 2 inches off, which on the 85 @ 1.8 is quite annoying).

 

Canon quoted me $185 for the adjust on the dRebel *plus* $125 for the adjust on the 85mm! Yikes! $185's probably more than the body is worth at this point, and $125 is 30% the price of the lens (new). Needless to say I turned it down and will learn to live with the glitch.

 

You sent in multiple lenses? How much was *that* repair bill?

 

On that matter, the mis-focusing still pains me, anyone know of a shop that can tune 300D bodies, all it needs is a focus adjustment; from seeing the adjustment screw in the chamber, this would *seem* to be a simple solution, but for some reason it's coming out to be almost $200.

 

Very frustrating.

[bobatkins]

Adams wasn't always right, or at least people don't always read exactly what he wrote.

 

DOF changes from an even 50/50 split in front of and behind the focus point for macro work to a 1/infinity split when focused at the hyperfocal distance.

 

Somewhere it's a 1/3 to 2/3 split, at some distance with some lens at some aperture. Somewhere else it's 1/4 to 3/4, somewhere else it's 3/8 to 5/8, somewhere else it's 1/16 to 15/16.

 

The 1/3 to 2/3 rule is a ballpark estimate. It's like saying the distance bewteen US States is typically around 1000 miles. In general, it's sort of true some of the time. It's an order of magnitude estimate.

[steve_dunn2]

<cite>If I point the red focus point on the subject's eyes, shouldn't this be the sharpes point in the picture with 1/3 in front and 2/3 in back acceptably sharp?</cite>

 

<p>Technically, only the subject's eyes (or anything else at the same distance) is actually in focus. Everything else which is within the DOF is technically not in focus, but appears to be acceptably sharp.</p>

 

<p>Enough of being pedantic :-) Everything within the DOF should appear acceptably sharp. Depending on the resolution of the sensor, the monitor/printer, how good your eyesight is, how picky you are, etc., you may be able to see that the bit that's actually truly in focus is slightly sharper than the rest, or you may not.</p>

 

<p>If you focused on the eyes, and the nose is sharp but the eyes are not, then we're not talking about DOF here; the focus distance selected by the camera was on or near the nose, not the eyes. This could be human error, though in your case it doesn't sound like it since you were using a tripod and since you can reliably get good focusing with the same body and a different lens. This could be that the camera's AF sensor is larger than what's shown in the viewfinder (so while the viewfinder shows it on the eyes, it actually covers the eyes and the nose and could potentially lock onto either) or is in a slightly different position than shown in the viewfinder (so while an eye was in the little box in the viewfinder, the AF sensor might actually be looking at the nose); given that it works properly with the other lens, this probably isn't it, though the difference in focal lengths and DOF with the other lens could impact on this. Or it could be the infamous problem that happens with some bodies and lenses in which the camera frequently focuses either behind, or in some cases in front of, where it should.</p>

 

<p>Have a look at the focus accuracy testing portion of dpreview's tests of recent bodies for an idea on how you might test this. Basically, they have a ruler on an angle, so you can see which ticks on the ruler are or are not sharp, and a fairly large target for the AF system, so you know the AF system hasn't accidentally locked onto a part of the ruler that's in front or behind. I don't know if a camera technician or engineer would approve of this test but it seems logical enough to me.</p>

[jose_marin]

I contacted Canon as the location I focus in should be in focus (as sharp as possible within the F/stop chosen) and DOF should play out with it's respective 1/3 - 2/3 DOF. I was told by Canon that I needed to send the camera and lens to a Canon Authorized Service Center (of which there are only 3 in US) so they can have the lens properly aligned to the camera. I was apalled about this and asked how Canon, with it's reputation, have this kind of an answer. They said that not all lenses are built the same and that the lens could be adjsted to ensure optimum performance from the body it was attached to.

 

I opted not to send the system to Canon, but to speak to the company that sold me lens to have another one sent out. I'm hoping that the lens that was sent has a problem, otherwise, I'm going to be veeerry dissapointed. I thank everyone for your input and hope for the best going forward...

[aleksandar_kujucev1]

"David Freeman , mar 08, 2005; 10:10 a.m.

"I took all seven of my lenses and they calibrated the camera for the correct "AF stop point" of each lens (which due to the age, or manufacturing variations is unique for every sample)."

Where did you take your equipment? Directly to a Canon service facility? How long did it take to get your equipment back? Thanks."

 

I took it directly to the Canon service - it is in my town, so I just walked in. It took them only three days to do it :-)

 

"You sent in multiple lenses? How much was *that* repair bill?"

 

It was free since my camera is under waranty...

 

"Canon quoted me $185 for the adjust on the dRebel *plus* $125 for the adjust on the 85mm!"

 

I don't know why they are charging you for the lens, since IMO all adjustment is done on the camera only!

[ilya_nazarenko]

Gentlemen,

 

Just to help clarify this ?complicated? subject of Canon autofocusing I would like to share with you my saga of acquiring this wonderful piece of sh? (equipment) that I would call a ?lemon? (and I can assure you that you can find a lot of frustrated people who were and/or will be in the same situation as me).

 

I bought my Canon 20D with Canon 17- 85 lens in December of 2004 and at the time I did not know anything about this problem that Canon was having with digital SLR?s (otherwise as you can guess they would not get my business). I discovered pretty soon that I simply could not obtain a sharp picture of any object (in fully automatic or manual mode). I started searching on the web and sure enough I found dozens of complaints about the same problem. I followed up with the test http://www.photo.net/learn/focustest/ and it confirmed that I was having autofocus problem.

 

I called Canon and explained the situation to a rep. He logged the problem (I registered the product online after I received it) and told me to send the camera and the lens to their authorized center in New Jersey for calibration. HE TRIED TO GET ME TO PAY FOR THE SHIPMENT! I yelled at the supervisor and they picked up the shipment cost. I sent it in and got it back in a week with the same result ? nothing was fixed. I called directly to New Jersey plant and was told that they did not know what the problem was since I did not include the description of what was wrong (have they ever heard of a database?). So, I sent it in again (they picked up the cost again) this time with all test pictures and detailed description of what the problem was.

 

They ?reset focus to spec.? and I was happy that now I am going to be taking pictures with confidence that the main object is going to be in focus (I checked and it worked. They fixed it). The only slight problem - the lens?s outer plastic ring was cracked and I could not install any filters (not to mention that this lens has a stabilization mechanism).

 

So, here we go again. I called the New Jersey plant, they sent to me the shipping slip, I sent the lens and it took them about three weeks to replace this piece - of course they did not have it in stock.

 

I got it back last week and what I discovered was that the camera did not allow me to focus on any vertical lines (so if I have to perform the above-mentioned test I have to make sure that my center focus point is set on the line?s end, otherwise the camera does not focus. It focuses on the line just fine with any other focus point or if I turn the camera 90 deg.

 

So on Monday they I going to hear from me again.

 

Good luck with your endeavor and I hope this little story will help you make the right decision.