Canon 70-200mm F4L Users advice needed

[Roberteo]

Need you expert to verify my 70-200mm F4L lens on back focus problem.

http://www.pbase.com/image/53494110

70-200mm F4L @ 200mm F4L


http://www.pbase.com/image/53494186

50mm F1.8 @ 50mm F1.8

Please advice if this considered within manufacturer's tolerance or it is out of focus.
And also how long Canon usually takes to Re-Calibrate a lens.

[user111]

looks like a bit of back focus on the 70-200 f4 because the text is less in-focus as compared to the 50/1.8

[Roberteo]

Thank you for your prompt reply USER111. The question is, is it within the manufacturer's tolerance!

[user111]

all i can tell is that its 2mm off

u have to check the lens/product literature for tolerance of thsi lense..and i dunno where to find it

[madmacs]

do you have more shots at different focal lengths? slight back focus on the one you show but seems to be reasonably sharp still. maybe show us a 100% crop of the target area.

i had my 70-200 f4 calibrated at canon - took about a week before they told me that my lens was ok on their test 10d. i had to bring in my 10d for them to test and confirm that it was backfocusing badly. the calibration itself took less than 1 hour.

i think your backfocusing is very slight. but if you are not happy with it, send it in to canon anyway. you should send in your camera together with the lens regardless what the front desk says.

[USM]

Why waste money on calibration? If it's only slightly out, just bear with it.

Do you have a actual photo (not test chart) of the lens taken to show the seriousness of the back focusing problem? This is help you to determine whether it's worthwhile to send it in for calibration.

[Roberteo]

Will post some photos later.

[mpenza]

actually, it looks quite okay. btw, mine back focus only at 70mm. at longer focal lengths, the focussing was pretty spot on. Canon Singapore took less than a week to calibrate the lens.

[holeinone]

I think your lens looks ok. Even if there is any back focus issue, it's very very slight.

For one thing, the test has to be done properly to get accurate results. For all you know, the so called backfocus can be resulting from test error?

[Roberteo]

Funny, test chart looks abit back focus, but flat picture tested ok (100% cropped).

http://www.pbase.com/image/53512346


http://www.pbase.com/image/53512370


Object distance is around 1.3 meter (parallel to the camera).
1) Set focal length to 100mm.
2) Focus on the subject.
3) Switch the lens to manual focus mode.
4) Set exp
5) Fire.
6) Repeat step 2 to 4 (set apperture to F8 and F16 respectively)
7) Set focal length to 200mm.
8) Repeat step 2 to 6.

I can now confirm that the lens is alright.

You guys are really really helpful and envy your experience.

[majere2sg]

One question, is the test performed mounted on tripod ? If it is, then how come flash is needed here ?

[Canew]

Originally Posted by USM Why waste money on calibration? If it's only slightly out, just bear with it.

For warrantied lenses, do calibration costs money?

[madmacs]

Originally Posted by Canew For warrantied lenses, do calibration costs money?

free if under warranty

[madmacs]

Originally Posted by Roberteo Funny, test chart looks abit back focus, but flat picture tested ok (100% cropped). http://www.pbase.com/image/53512346 http://www.pbase.com/image/53512370 Object distance is around 1.3 meter (parallel to the camera). 1) Set focal length to 100mm. 2) Focus on the subject. 3) Switch the lens to manual focus mode. 4) Set exp 5) Fire. 6) Repeat step 2 to 4 (set apperture to F8 and F16 respectively) 7) Set focal length to 200mm. 8) Repeat step 2 to 6. I can now confirm that the lens is alright. You guys are really really helpful and envy your experience.

the "backfocus" you encountered might be because the target area is slightly smaller than the af sensor. hence the sensor may have focused behind the target. this is actually explained in one of the canon articles..i think for the 1d.

btw the test board used by canon has this huge target area sticking out like a 12" ruler.

anyway based on your last pics, your lens looks quite sharp.

[holeinone]

Sharpness and backfocusing are 2 different things what.... A sharp lens can also backfocus.

[Roberteo]

To majere2sg, the test were performed on my Gitzo 1212 without flash.

To madmac, you wrote that the lens is "quite sharp", but most of the review on this lens were very sharp, quiet, speedy focusing. Is the camera or the lens that is causing the not very sharp problem. Anyone with the same setup please please advice. Because I feels that too, especially taking RAW. Thx!

[Canew]

Roberteo, I can test out my copy. Care to share your set-up so that I can replicate your test? And then maybe I can post my pictures too. Then we can compare.

[Roberteo]

Thank you Canew. Here is my setup,

Body - 350D
Lens - 70-200mm F4L
Flash - Nil
Tripod - Gitzo 1212
Subject - Canon 70-200mm F4L Box (the side with red stripe)
Focal Length - 100mm and 200mm @ F/4, F/8, F/16
Lighting - Ceiling flourescent about 2.5M high.

Camera elevation at around 1.4M, level with the help of the level gauge.
Place the subject about 1.3M away from the camera, make sure subject is parallel to the lens, set focal length to 100mm, focus on the no. 4 of f/4L USM print (adjust column height if neccessary), pan your camera to focus on far object, pan back to subject's focus point, set lens focus mode to manual, set exposure and take your shots.

ISO 200
Quality = L
AF mode = One Shot
Metering = Evaluative
Mirror Lockup = Enable
Shot taken with timer.
SUTTER
F4 @ 1/30
F8 @ 1/10
F16 @ 0"4

Like to see your posting soon. Thx

[madmacs]

Originally Posted by Roberteo To majere2sg, the test were performed on my Gitzo 1212 without flash. To madmac, you wrote that the lens is "quite sharp", but most of the review on this lens were very sharp, quiet, speedy focusing. Is the camera or the lens that is causing the not very sharp problem. Anyone with the same setup please please advice. Because I feels that too, especially taking RAW. Thx!

as holeinone corrected me...i should have said your lens focusing in pretty much on target.

as for the lens backfocusing, the problem can be with the lens or with the cam. in my case i think the problem is with my 10d since i had to get both my 24-70 and 70-200 calibrated. also my 70-200 was spot-on when tested with canon's inhouse 10d. if your lens or cam still under warranty and you are not too comfortable with the focusing, send both in to canon for testing and calibration.

btw..you might want to enlarge the target area or use the other test chart posted by usm in another thread yesterday. this will give the af sensor a better chance of correctly focusing on the target.

[Roberteo]

Just found out another test chart @ http://www.canon-dslr.com/Canon_Jan0...Focus_Test.htm.

Going to try out 2morrow if have time.