back focussing 70-200f4L

[jtfoto]

Please excuse this question if it's been addressed before but searching the forum did not help.

I have only just had a chance to really use this lens which I purchased some time ago and it seems that unlike my 17-40f4L and 50 1.8 this lens does back focus wide open.
It seems to be maybe 2-3 inches behind at between 5 - 10 yards. It appears to be worse at the long end.
My question is has anybody else experienced the same problem and if so was it resolved and how?. I'am hoping Canon Australia has the smarts to rectify this.

[roanjohn]

2-3 inches, thats way back focused!!! Send it in for recalibration..........or if the lens is new, get another copy.

Ro1

[JK]

Ah, weclome to the club!

My 70-200 went straight to Canon's service centre in Perth a few days after it arrived. It was tack-sharp at 200, but back-focused from 70-135. Grrr!

Anyway, they made "a minor adjustment" which has improved the situation, but I'm still not entirely satisfied. So it looks like it'll go back to the service centre again soon.

(I did check my 300D with other lenses first to make sure that the camera wasn't at fault)

Sigh!!!!

[tpinchback]

backfocusing is common with this lens

[jimlp]

I am a member of the club as well. My 28-70 f2.8 works great on my 20D but my 70-200 is back focusing at all focal lengths and at all apertures. This lens worked on my 10D and had originally worked on the 20D but not anymore. It is really weird as the 70-200 works fine on my 2 film bodies as well so I guess I will send it to Canon and see what they say.

[Johnny V]

>Ah, weclome to the club!

Hey wait! That was my line!

Purchased same lens about two weeks ago. Tack sharp at 200mm but back focuses badly at shorter end.

Same with 17-40 and 50 1.4 all need focus fixed...the 17-40 needs more fixes as it is soft on the sides even when stopped down and this is my second copy too.

Will send all to Canon for calibration.

The Nikon Gods are not too happy with me!

[JK]

Same with 17-40 and 50 1.4 all need focus fixed...the 17-40 needs more fixes as it is soft on the sides even when stopped down and this is my second copy too.


Given that you've got focus problems with other lenses, could there be a fault with the camera ?

(All of my other lenses work ok, except the 70-200, hence my reasoning that the lens was faulty)

[Johnny V]

Sure it could be my Rebel. This one is my second Rebel as the first one had image smearing in the corners and focused even worse. The Rebel body is going to Canon too just incase.

I'm not really that happy to tell you the truth. Been using a Fuji S2 for a couple of years and other digital 35mm Canons too and no problems. Switching over to Canon has left a sour taste in my mouth. I just hope Canon resolves all the problems...I'm not selling any of my Nikon gear until Canon fixes this.

[theflyingkiwi]

Is this problem common with this lens? does anyone know if the simga 70-200 f2.8 have this problem?

[hank1105]

Not to steal your thread, but what is back focusing? Thanks.

Hank

[TomC]

Not to steal your thread, but what is back focusing? Thanks.

Hank
Back focusing is when the lens focuses in on a spot short of where you actually intend the focus to be. It is usually mm below your intended spot but not usually 2-3 inchs as indicated above. Thats a bad problem!

[Johnny V]

Back focusing is when the lens' focus point is behind or past the intented focus point. The lens focuses further away then needed

[TomC]

Back focusing is when the lens' focus point is behind or past the intented focus point. The lens focuses further away then needed

That too :)

[jeric777]

im also having this problem with my 70~200f4 lens, exactly what jtfoto is describing.Canon should make a custom setting for this, like FEC, you can set focus compensation.

[21farms]

Is this problem common with this lens? does anyone know if the simga 70-200 f2.8 have this problem?

i'm not sure just HOW common this problem is but the "classic" symptoms are perfect focus at 200mm but backfocusing that gets progressively worse as you go toward the 70mm end. i too had a 70-200/f4L that did this. the irony is, i bought the 70-200/f4L because i had sent my sigma 70-200/2.8 in for FRONTfocusing and i needed a lens right away to tide me through the beginning of soccer season! anyway, sigma kept my lens for 2 months before finally sending me a new lens (which worked properly). the canon, OTOH, came back only slightly better so i sent it in again. it came back slightly better but still exhibited frontfocusing so i sent it back AGAIN. finally, it works likes it is supposed to. the tech i talked to said they replaced the entire AF mechanism and, let me tell you, it is like a different lens! it used to exhibit what i call "second guessing"...in other words, i had the camera/lens mounted on a tripod and pointed at a high-contrast target in good light but, yet, each time i'd half-press the shutter button, the distance scale would jump, landing in a slightly different place each time. now, it doesn't do that anymore; with each half-press, the distance scale doesn't move unless i've changed something else. the AFing is quieter too. i cannot tell you how much i love this lens now...it is sharp, sharp, sharp.

[hank1105]

Thanks for the info, just tried my 70-200 f/4 to see if I had the same issue, everything was fine.

Hank

[cricket]

Does anyone know if this is only on the 70-200 f4L? Any mention of the 70-200 f2.8L?

Are any of these the IS / USM models?

I'm thinking of getting the 70-200 2.8L IS USM, and also had never heard of back focusing!

[JK]

Does anyone know if this is only on the 70-200 f4L? Any mention of the 70-200 f2.8L?

Are any of these the IS / USM models?

I'm thinking of getting the 70-200 2.8L IS USM, and also had never heard of back focusing!
The 70-200 F4 seems to be the main culprit when it comes to back focusing.

Though any lens can suffer from back or front focus issues really, so sometimes it's just the luck of the draw. The 2.8L IS doesn't appear to have this problem, though I have read posts from people who have had it lock up their camera on them - sigh!!!

[planesh00ter]

Hope this doesn't sound toooo stupid but this in the AF mode only right?

[jtfoto]

Well thank you all, I now don't feel like I am imagining things.
Looks like it's off to Canon we go for calibration and hope we can get it right first time.
Thanks again.

[JK]

Hope this doesn't sound toooo stupid but this in the AF mode only right?
Correct - I use AF to focus on an object at 70mm and it's just a bit fuzzy. Manual focusing on the same object yields a crisp image. It doesn't happen with my other lenses and is a VERY annoying little problem!

[BoySpot]

I am going to ask what may be a dumb question but here goes. Why is a lens responsible for back focusing? The camera has the auto focus control and drives the lens to move until a focus is achieved. Does the lens have any intelligence in this process? In my simple view of the process, any problems with focusing would have been as a result of the camera not driving the lens to the right place.

How does it really work anyone?

[ILoutdoorcpl]

What is the cause and cure for this problem? I have the 70-200 but havent noticed any problems yet.

[cricket]

So, if we test our lenses, now that we have been warned of this, and we notice a problem...

Canon will not automatically replace the lens, but will attempt to rebuild the autofocus motor?

[21farms]

ILoutdoorcpl, not every 70-200/4L has this problem. if you haven't noticed anything amiss, you're probably fine. in fact, i'd imagine that 98%+ of 70-200/f4Ls are fine.

cricket, your retailer may replace the lens for you but canon's policy is to re-calibrate the lens. the good thing about canon's service is that they are fast (i usually get mine back within 10 days of sending it in) and the tech will center the calibration to the middle of their spec which should be a lot tighter than when it leaves the factory which could be anywhere within the spec range.

[digitalfailure]

please excuse the dumb n00b questions

But

How would you test this lens for the back focus concern?

I was short listing this lens as a replacement for my 75-300 IS

[JK]

So, if we test our lenses, now that we have been warned of this, and we notice a problem...

Canon will not automatically replace the lens, but will attempt to rebuild the autofocus motor?
If you notice a problem, return the lens to the store where you bought it and ask for an exchange or refund. Failing that, Canon can re-calibrate the lens to resolve the problem.

Having said that, my lens will be going in to Canon for its second "re-calibration" - I should have taken advantage of B&H's exchange offer instead - grrrrrr!!!!