How simple is it to fix a front focussing lens?

foodpoison

foodpoison

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Sean
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I first noticed a problem with the AF on my 24-60 in New York. I thought it was because of the strange lighting/patterns and the camera was having trouble.
Turns out it's rubbish.

The camera is focussing just ever so slightly in front of the subject.
I know it's the lens because this doesn't happen with my 55-250 (and i'm pretty sure it doesn't happen on my 10-20 either :p)

I say how simple to fix, more like how difficult.
Is it a case of sending the lens back to Sigma (it's under a year old so manufacturer's warranty still applies) and getting it re-calibrated?
 
I've been reading that slight front focussing is intentional, since the dof is distributed across the frame, it's just in the vf it looks slightly out of focus, causing me to worry, and when shooting flat subjects such as paper it looks out of focus, yet I'm not concerned by the sharpness of ANY of the photos from new york nor am I concerned by anything else I've taken photos of.

Pixel peeping isn't something I do, because it's very much a whirlpool of disappointment, so is this just a case of putting up with something that's not actually too much of a problem?
 
If you have good reason to believe that your lens/camera is misfocusing, then you need to test it properly. I would advise against using the infamous method commonly used which involves shooting an A4 sheet of paper at 45 degs - while it should work in theory, it is unrealistically critical and most people seem to get it wrong, and therefore appear to find fault with perfectly good lenses.

If your lens is significantly out, then I guess it's a job for the manufacturer.
 
See I don't want to go looking for problems when overall I'm happy with the sharpness of my lens, it's just when testing it, it focusses ever so slightly in front of the subject causing it to be soft.
But it's only an issue when shooting flat things like newspaper at a 90 degree angle.
 
I had an issue with one of my more expensive Nikon lens, the 24-70. I was often dissapointed with the results when used at 24mm. That's what prompted me to give it a test, actually, that's what made me test all my lenses (not something I would have done otherwise).

It turned out there was an issue with front focusing (the minimum focusing distance of that lens is about 30cm .. and the front focusing problem was 6~10cm). The only thing I thought logical was to have it sent back to Nikon for repair.

On mentioning that problem here, puddleduck confirmed to me that the lens is known to have such a problem at 24mm when wide open (which was exactly my case). Anyways, lens was since fixed and returned to me; but it took close to 6 weeks to get it sorted :shrug:

I've since sold the lens here, and the new owner seems very happy with it.

So, to answer your question (sorry to make it long) .. it's not as simple to fix as I thought. Nikon did request me to send them photos (NEF) to demonstrate the problem :shrug: .. I would have thought they had equipments to quickly test this, but I guess not.
 
If you're at all concerned I'd get it off to Sigma for re-calibration. It can't do any harm can it?
 
it has obviously bugged you enough to post it here, and since you still have a warranty, get it back to sigma and let them fix it. then it should come back perfect and you will be 100% happy as opposed to 90%.
 
foodpoison said:
See I don't want to go looking for problems when overall I'm happy with the sharpness of my lens, it's just when testing it, it focusses ever so slightly in front of the subject causing it to be soft.
But it's only an issue when shooting flat things like newspaper at a 90 degree angle.
Click to expand...

Once you start looking for problems, you'll find them, even if they are so slight as to make no difference ;)

In practise a very slight amount of mis-focusing by the camera passes unnoticed, as it's usually less than any mis-focusing caused by the user not choosing the optimum point to lock on to, and most errors are covered by depth of field anyway.

But once you know it is there, the seed has been sown and it will nag away at you. It would me.

Speaking for myself, I would make sure my tests were sound and that the lens indeed had a significant problem that was big enough to bug me, bearing in mind no lens/camera is 100% perfect 100% of the time. I would then check how long it would take to get calibrated and work around that maybe borrowing another lens if desperate.
 
I'm going to try and ignore it, but if it DOES bother me again, I'll test it to see if there's actually a problem, if there is, I'll send it away. I'm reluctant to send it away since it's my standard lens. I could go without the 10-20 or the 55-250 but I need the 24-60!
 
Don't you have a 35 ~ 50 prime to bridge you over the period while it's in service?

When my 24-70 was away, it took what seemed forever to get back; thankfully my 50/1.8 and 58/1.4 helped me to keep my sanity .. otherwise God only knows what would have happened to me.
 
That's a shame .. and always the case. Just when think you no longer need that extra bit of kit, you sell it, then shortly thereafter you find yourself badly needing it :p .... happens to me all the time.
 
david1701 said:
you can adjust the calibration on a 50d so i think you can on a 40d its a CF I think
Click to expand...

Just to clarify: this was a new feature on the 50D and is not present on a 40D.
 
perhaps speak to the manage bout "borrowing a lens" fromwork while it is fixed?

or spend £30 on a cheap kit lens to keep you going?
 
Get it sent off!
Think of the resale in future, what if the person who buys it isnt happy with the focusing and sends it back to you etc. Send it off now while its less than a year old and get it sorted like i have with the 24-70 (Even though i'm paying £33.99 for mine as it was from HK)

Mike
 
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