100-400mm Canon Lens Focusing problems! need advice

I bought the 100-400mm not long ago and tested it out here and there for a few days. Took a few bird pictures using the center focus point on my 50D and found majority the eye was out of focus even though i focused on the head of the bird.

I used it further and felt there was problem with the auto focus. The lens is sharp and very good, its just the AF seems to be off. Never had any problems with any of my other canon lenses which have been absolutely fine.

Today i tested it with a ruler, 45 degrees to the camera. Took a few hundred shots. Results were fairly disturbing. 1 in 20 or less were right on the mark. Either focusing behind or inffont of the mark. I would manually make the picture out of focus then let if AF to the center point and then take the picture.

I did some shots at f7 and some at f5.6. The ruler i used was matt silver and it was well lit. Usinf iso 200 and shutter speeds 1/800 - 1/1000 on a tripod without IS turned on.

here are a series of 6 shots. Cropped a little. The center focus point was essentially on the 15 or very close to.













It seems to be a problem where it focuses randomly behind and infornt. Took some pictures on a different body (1000D) with the same sort of results.

My question is, what can i do? I am in Australia, bought the lens new less than a week ago. Has anyone returned/sent away a lens and how does it work? Not fimilar with the process as it is the first time a lens has played up noticeably.

Thankyou

First of all...turn-off the IS when your using the tripod. Second, look at your DOF. Re think your testings. Get out and take real-life pictures to test your lens. One more thing, the 50D has micro-adjust. My 100-400mmIS was adjusted to +7. Every lens is different, so look into this.

yes, micro adjustment. But if it is focusing back and forward how can micro adjustment help?

get out into field and take some pictures and micro-adjust. I was at the airport to take some pic's and I micro-adjusted +7 at 400mm. It was spot-on.

Are you moving the tripod at all or changing focal length between each shot?

not moving the tripod. Just moving the focus ring to make the picture out of focus then half press to let the camera auto focus. Aiming directly at the 15.

Looking at a few pics it loosk like back focus. Then it starts focusing forward. I dont think this is normal. Out of so many shots the 15 is hardly in focus ever.

The A/F sensor is considerably bigger than the spot in the viewfinder, so pointing it at a reflective subject with a few black markings on it and expecting the camera to know you want it to focus on the "15" is being unrealistic. Put a heavy black cross where you expect it to focus if you insist on shooting rulers, or try a series of dark batteries against a light background or vice-versa. It is more likely your test is flawed, rather than the lens/camera

Its not really reflective. Matt aluminium. I dont understand how it doesnt want to focus correctly on the center point when it just as easily wants to focus on the other numbers around it. The ruler is essentially uniform, there is nothing easier for it to focus on just doesnt want to focus on that 15.

Fabian628 said:

Its not really reflective. Matt aluminium. I dont understand how it doesnt want to focus correctly on the center point when it just as easily wants to focus on the other numbers around it. The ruler is essentially uniform, there is nothing easier for it to focus on just doesnt want to focus on that 15.

Click to expand...

..What part of "The A/F sensor is considerably bigger than the spot in the viewfinder" don't you understand ? The A/F sensor probably covers an area from 10 - 18 on your ruler - anything with reasonable contrast WITHIN THAT AREA can be picked up by the A/F system as a reasonable point to focus on. Due to the depth of focus being so narrow at long focal lengths, then of course anything more than a short way outside the ACTUAL point the camera has chosen will appear out of focus. If you actually listened to advice and tried to focus on an area that had ONE high contrast spot, then you might see what was actually going on - or (horror of horrors) actually go out and try and take an image of a bird in a tree rather than wondering why the lens hates the number 15 ! Looking at your images - if you took the ruler away and just focussed on the diagol branch you would probably have more success. BTW being an Australian isn't an excuse - I am one as well ;-)

What PhillipA said.

I thought it was well-known by now that trying to AF on a a scale placed so that it recedes diagonally from the camera was a completely unsatisfactory way to test AF. You need a high-contrast flat subject placed at right angles to the lens axis and large enough to cover the whole area of the active focusing "point". When you have focused on that (transfer AF to the * button to ensure that it is disabled on the shutter button, you don't want to re-focus as you take the shot), replace the focusing target with your diagonally-placed scale, making sure that the "zero" of the scale is at the point where the lens axis intersected the target, and release the shutter.

You can also try it with some batteries placed on diagonal. Try to focus to a different battery each time from the line.

just looking for some advice as i am not fimiliar with these kinds of lenses. Your information was useful. Thankyou.

You need to do the test with reasonable subject distance, i.e. don't go too close to the 1.8m minimum focus distance.

I don't go with this stuff about angled target under certain conditions it is OK. If the target is covering the focus point and is angled by about 45 degrees, it doesn't actually make much difference, so long as the depth of focus is significantly more than the focus point area. This does not seem to be the case with your tests, so an angled target WILL make a difference.

Try backing up a bit and repeating your test with a flat target that covers the focus point area (i.e. more than just the focus indicator square in the view finder).

You should really do the tests at 50 x f, i.e. 50 x 0.4 = 20m. But 5m is OK for practical reasons.

I accept you also want focus accuracy at 1.8m (min focus distance) and f=400mm, but check out the normal focusing first.

thanks, i will keep this in mind

GoldenSpark said:

You need to do the test with reasonable subject distance, i.e. don't go too close to the 1.8m minimum focus distance.

I don't go with this stuff about angled target under certain conditions it is OK. If the target is covering the focus point and is angled by about 45 degrees, it doesn't actually make much difference, so long as the depth of focus is significantly more than the focus point area. This does not seem to be the case with your tests, so an angled target WILL make a difference.

Try backing up a bit and repeating your test with a flat target that covers the focus point area (i.e. more than just the focus indicator square in the view finder).

You should really do the tests at 50 x f, i.e. 50 x 0.4 = 20m. But 5m is OK for practical reasons.

I accept you also want focus accuracy at 1.8m (min focus distance) and f=400mm, but check out the normal focusing first.

Click to expand...

If I was a camera I would not know on which part of the ruler I should focus on. You need a test setup where the autofocus sees just a sinlge line to focus on. The ruler should be outside of the focus area and just show where the focus ended up.

I went out to take a few pictures of birds, mostly ducks on the water. Focusing the center point on thier head, side on the results were mostly, what felt like, slightly out of focus. When it hit spot on the picture is very sharp and good detail. But when it is slightly out of focus you lose the glint in the eye and it really isnt pleasing. Majority of the shots were slow/ no movement and high shutter speeds, so camera shake could not have been a cause.

I love the colour/contrast, sharpness and background blurr of this lens! its great, only thing is the AF. It seems very hit and miss, and to be honest i am not THAT picky about my lenses IQ, its just this stands out alot.

I did another test, this time on a piece of paper with a scale on it. Focusing the center point on the black line. Sometimes it focuses behind other times in front. Very inconsistant so i fear micro adjustment will not fix the problem.

here are the pictures below, IS is off, pictures at 1/400s iso 500 or there abouts, using a tripod.

















I also used my 60mm macro lens on this target to see the result. It focused very slightly back of the target every time. I micro adjusted a little forward and it was perfect.
I do feel the AF should be better than this in my lens. Any thoughts?

Its not that easy to set up a valid focus test. I have made controlled test runs using three different methods to find out the most reliable way to microadjust my lenses. I was surprised how difficult it was to get consistent results.

http://forums.dpreview.com/forums/read.asp?forum=1029&message=31465036

Its more work, but the results will be meaningful and consistent.

i read your link. Whould i do all the tests? What encomasses the ruler test?
Could you explain them in a little more detail.

Thanks for your help in advance

maiaibing said:

Its not that easy to set up a valid focus test. I have made controlled test runs using three different methods to find out the most reliable way to microadjust my lenses. I was surprised how difficult it was to get consistent results.

http://forums.dpreview.com/forums/read.asp?forum=1029&message=31465036

Its more work, but the results will be meaningful and consistent.

Click to expand...