Does anyone has 20D that AF incompatible with 85mm f1.8?

[megaweb]

Does anyone has 20D that AF incompatible with 85mm f1.8?

I am experience focusing problem and all my shots turn up soft.

see here for detail
http://forums.dpreview.com/forums/read.asp?forum=1019&message=11722729


Does anyone has the similar problem ?

[cactusclay]

That's interesting. I was just complaining about my tamron 28-75 and thinking about sending it back and getting a 85 1.8. I never heard of any incompatibility issues. Is there a filter on it?

[megaweb]

See the test result at the link.

I did some focusing tests and using Auto Focus, I get soft images and Manual Focus, I can sharp images. I do not think is due to filter issue. I do not have such focusing issue on my previous D60.

My setting for 20D is
- 1 AF pt at center
- Single shot
- @f1.8
- working distance abt 1 to 2m
- ISO 800 at indoor

I do not have focusing problem with other lens, 35mm f2, 100mm macro and 70-200mm f2.8 L IS. I suspect 20D has AF focusing issue on certain lens like 85mmf1.8.

[jimlp]

I find this strange considering the lens just came back from Canon and should be working fine, I would send it back but I would call them first and make them pay shipping both ways. I hope I have better luck than you did as I just sent my 70-200 f4L in for the same problem, luckily mine is still under warrenty but it is still a pain in the ass!

[CyberDyneSystems]

Mega.. the filter thing is a looong shot,.. but it does happen from time to time. You may want to try it out.

Otherwise.. I would send that lens back. I just got an 85mm and it focuses super fast on the 20D and is quite nice. You may have just gotten a bad copy.

[drisley]

MY experience is the same as CDS.
Super fast focusing and sharp images with the 20D and 85F1.8 combo.
This was taken at F2.2 at ISO1600 (http://www.fotop.net/albums/sharpnsmart/hockey10242004/MG_3219.jpg)and is sharp enough to blend well with my 135F2L shots.

[charlesu]

My 85 1.8 works great!! Love it on the 20D!

[PacAce]

Try taking pictures of some real objects and see if you're getting the same thing. Taking a picture of a ruler really isn't going to give you a true indication of a focus problem because of the size of the ruler you are focusing at. A good one would be to shoot a whole bookshelf full of books at a 45 angle. Pick a book in the middle of the shelf to focus on and see what you get. I think this would be a better test than a small ruler. If the focus is off, you'll see books on one side or the other of the book you actually focused on.

[robertwgross]

I would start from the standard tilted ruler test.

However, a tilted ruler in dim light may not cut it.

I would add a bright red nail head or bright red tack to the intended focus point, like 8 in the test.

Now shoot it again. See if it still goes off to 7.

---Bob Gross---

[megaweb]

Mega.. the filter thing is a looong shot,.. but it does happen from time to time. You may want to try it out.

Otherwise.. I would send that lens back. I just got an 85mm and it focuses super fast on the 20D and is quite nice. You may have just gotten a bad copy.

Sure. Will try this evening for non-filter shot.

I already sent it to Canon for calibration and collected yesterday. The result is the same. My 85mm f1.8 is not new. It works well with my D60 and EOS 30.

Regards

[megaweb]

MY experience is the same as CDS.
Super fast focusing and sharp images with the 20D and 85F1.8 combo.
This was taken at F2.2 at ISO1600 (http://www.fotop.net/albums/sharpnsmart/hockey10242004/MG_3219.jpg)and is sharp enough to blend well with my 135F2L shots.
very nice. How about focus on some words on an object ?

[megaweb]

My 85 1.8 works great!! Love it on the 20D!
Glad you have no problem :)


Try taking pictures of some real objects and see if you're getting the same thing. Taking a picture of a ruler really isn't going to give you a true indication of a focus problem because of the size of the ruler you are focusing at. A good one would be to shoot a whole bookshelf full of books at a 45 angle. Pick a book in the middle of the shelf to focus on and see what you get. I think this would be a better test than a small ruler. If the focus is off, you'll see books on one side or the other of the book you actually focused on.
Sure. Will try to take some similar shots. BTW, what is the working distance ?

I would start from the standard tilted ruler test.

However, a tilted ruler in dim light may not cut it.

I would add a bright red nail head or bright red tack to the intended focus point, like 8 in the test.

Now shoot it again. See if it still goes off to 7.

---Bob Gross---
Look forward to see your result :)

[megaweb]

here is my 85mm f1.8 USM focusing test at outdoor
settings as usual , no re-compose, single shot, 1 AF center point, @f1.8, Av, tripod, filter removed

Test 1
using Auto Focus and focusing at blue cloth peg,
http://megaweb.clubsnap.org/d20_test/85mm_1/img_8398_std.jpg

using Manual Focus and focusing at blue cloth peg,
http://megaweb.clubsnap.org/d20_test/85mm_1/img_8399_std.jpg


Test 2 - similar test cloth peg place further
using Auto Focus and focusing at blue cloth peg,
http://megaweb.clubsnap.org/d20_test/85mm_1/img_8400_std.jpg

using Manual Focus and focusing at blue cloth peg,
http://megaweb.clubsnap.org/d20_test/85mm_1/img_8401_std.jpg

more outdoor sample shots at
http://megaweb.clubsnap.org/d20_test/85mm_1/outdoor_01.htm


Do you think my lens has problem ? or 20D AF focusing has problem ? Or Portrait lens suppose to work like this ? Can someone enlighten me ?

[KennyG]

May I say I don't know how you can say you had focus on the blue peg. The area over which the camera will assess focus is much larger than the area you see in the viewfinder. The above shots are not valid for a test as the focus area probably covers all the pegs.

All lens tests, including those done by Canon, are of a high contrast object (black and white squares on non-gloss paper is good), parallel to the focus plane. So, you imagine you are taking the picture of a cereal box, square on to the side. Then, put a ruler at 45 or so degrees tilting up and away from the box, but in the shot. The sharpest point on the ruler should be that in direct line with the box.

Try printing a checkerboard pattern on a sheet of paper, stick it in the side of a serial box, use some means to prop a ruler running up and away at the right-hand side of the box, place the focus area to left of centre of the target to avoid capturing the ruler. Re-post the results.

I have details somewhere of the original Canon test rig which worked in the same way.

[Cadwell]

As Ken said, the actual AF point is larger than the square. It's grabbed the higher contrast of the white peg against the blue line and focused on that. Precisely what I would expect it to do under those circumstances.

That test proves nothing, I am afraid.

[KennyG]

Here is a 'quick and dirty' test using some batteries and the 85 1.8 wide open. You will notice that the target battery has a printed label to provide a high-contrast target. Shiny objects confuse the AF. The batteries are spaced about 1/2" front to back.

http://www.motorpix.co.uk/misc/ft.jpg

[megaweb]

Thanks KennyG and Cadwell for the reply

I find the contrast is not important as I already set to 1 AF POINT (CENTER) and the AF did focus lock on the blue peg. See other outdoor samples at http://megaweb.clubsnap.org/d20_test/85mm_1/outdoor_01.htm and all shots are soft taken with tripod support.

I did another test on D70 focusing chart from http://md.co.za/d70/chart.html
here is my test
http://megaweb.clubsnap.org/d20_test/85mm_1/img_8414_std.jpg

100%
http://megaweb.clubsnap.org/d20_test/85mm_1/IMG_8414a.jpg

Any comment ?

[KennyG]

The target contrast is absolutely important and key to any tests. You may assume it has grabbed focus on the blue peg, but the capture area is much bigger than you think and that is why you have to be careful of what you use as a target. You should get roughly 1/3 in front and 2/3 behind for the DOF coverage with my camera and my shot seems to verify this.

I don't like tests where you photograph targets at an angle as in your shot above. One reason is it only takes a very small change in the angle of shot to change the capture within the DOF and another is the target can be too 'busy' and you may stray out of the focus point. The actual target should be perpendicular to the plane of the camera and getting this accurate with anything else other than a flat perpendicular target is very tricky.

You also need to test more than one lens under exactly the same conditons to see if the problem (assuming there is one) is with the camera or lens. Don't forget, at 1.8 the 85 isn't very forgiving having such a shallow DOF.

[megaweb]

The target contrast is absolutely important and key to any tests. You may assume it has grabbed focus on the blue peg, but the capture area is much bigger than you think and that is why you have to be careful of what you use as a target. You should get roughly 1/3 in front and 2/3 behind for the DOF coverage with my camera and my shot seems to verify this.

I don't like tests where you photograph targets at an angle as in your shot above. One reason is it only takes a very small change in the angle of shot to change the capture within the DOF and another is the target can be too 'busy' and you may stray out of the focus point. The actual target should be perpendicular to the plane of the camera and getting this accurate with anything else other than a flat perpendicular target is very tricky.

You also need to test more than one lens under exactly the same conditons to see if the problem (assuming there is one) is with the camera or lens. Don't forget, at 1.8 the 85 isn't very forgiving having such a shallow DOF.

Ok. Let me follow your test on battery. I set 1 AF point at the CENTER, single shot and Focus at the center battery.

left = backward 1.5 cm from center battery
right = forward 1.5 cm from center battery

See
http://megaweb.clubsnap.org/d20_test/85mm_1/img_8421_std.jpg

Can you see the left battery is sharper ?

[CyberDyneSystems]

Dude.. your lens is BACK focusing for sure!

I was convinced with the papaer test.. the Clothes pin was reinforcing.. the battery test Clinches it!

I hate to say this,. but You may need to send the Camera and Lens to Canon for calibration... but it certainly is back focusing.

[KennyG]

You absolutely have a back-focusing lens by that test. What do your other lenses come out like by the way, just in case there is a camera problem. It is always worth running through all your lenses and get the pain over in one go.

[megaweb]

CyberDyneSystems & KennyG, thanks for the reply

I used AUTO FOCUS to focus lock the center battery, the results shows back focus problem. But if I use MANUAL FOCUS to focus the center battery, I can get center battery in focus and has sharp quality. When I use AUTO FOCUS, I can see that the focus point is soft and not in focus. So is it cause by lens or the camera ?

[Cadwell]

CyberDyneSystems & KennyG, thanks for the reply

I used AUTO FOCUS to focus lock the center battery, the results shows back focus problem. But if I use MANUAL FOCUS to focus the center battery, I can get center battery in focus and has sharp quality. When I use AUTO FOCUS, I can see that the focus point is soft and not in focus. So is it cause by lens or the camera ?

It could be either. Repeat the test with another lens. If it's still not focussing properly with another lens then chances are it's the camera (or you have two defective lenses - unlikely), otherwise it's the lens.

[Jon]

It could be either. Try running the test with a different lens; if that lens doesn't show the problem, or shows a different problem, it's the lens. If the other lens does show the same (order of) backfocussing, it still could be the lens, but is more likely to be the camera. Backfocus is essentially due to the signals between the camera and lens getting screwed up, but either the camera, the lens, or both could be glitching. When you focus manually, you're taking both the camera's and the lens' electronics out of the picture. Any problems there are caused by focussing difficulty in your eye :{)#

[megaweb]

I have tested all my lens on the D70 chart test

see
http://megaweb.clubsnap.org/d20_test/chart/chart.htm

look like 100mm macro and 70-200mm f2.8 does not have focusing issue on my 20D.

[BoySpot]

Forgive me jumping in to ask a separate question but how does the lens get it wrong? I assume the autofocus is control from within the camera based on what it is seeing through the lens. Doesn't the camera drive the lens until it finds a good focus? If so, how can the lens upset things. (I realise this seems to be the case given the test shots but I am confused as to how it can go wrong like this.)

Thanks

[robertwgross]

There are parts of the autofocus system in the camera and other parts in the lens.

Canon can calibrate each lens so that it hits the "middle" of normal camera calibration, and Canon can calibrate each camera so that it hits the "middle" of normal lens calibration. So, you can have either or both out of calibration and end up with poor results. That is why doing a ruler test with a single lens can lead to ambiguous results.

If one camera works good with one lens, and then the same camera does not work good with a second lens, that has to make you start to wonder. Sending the second suspicious lens to Canon for a calibration check is a good idea. Sending the second one along with the camera is an even better idea. Think of another scenario. What if the camera were out of calibration one way, and one lens is out of calibration the other way. Maybe they can cancel each other out at certain focal lengths, but not at others. I'll tell you, there are several different ways it can go bad.

You might ask the question... how does a lens go bad this way?

It is possible that the lens was mis-calibrated at the factory. Unusual, but certainly possible. It is possible that the lens was mis-handled since leaving the factory. More likely. One good drop and your autofocus goes weird. It is also possible that some electronic component has outright failed. Unusual, but certainly possible.

By the way, once the camera and suspicious lens have been re-calibrated, then get the previously good lens on the camera and see if it stays good.

---Bob Gross---

[BoySpot]

Thanks for the explanation. I guess I shall have to think about this a bit further. I was thinking that the camera looked at the image to drive the lens whichever way it needed. In that simple (too simple) analogy, the lens would be dumb in the whole process. That obviously isn't the case. Some quiet time required!