Front focusing issues

[robatkinson]

<p>I would appreciate some advice on some focussing issues that I am having.</p>

<p>I have a 7D body that is about 5 months old and recently bought a sigma 50mm f1.4 for it. I brought the lens home and tested out the AF seeing as the lens is pretty renowned for focus problems and I found that it pretty massively front focussed. So I took it back and exchanged it for another one which I tested just recently and it too front focussed pretty badly (about 4 inches in front of the test sheet which was about 8-10 feet away, although the first one was more like a foot). So, thinking that my camera body could possibly be calibrated a bit funny I test out my sigma 17-50 EX OS HSM and found that at 17mm it front focussed by about 4 inches and at 50mm it was pretty dead on over the same 10 foot(ish) test length.</p>

<p>So, question 1) is it normal for a zooms focus to vary that much over the focal length?</p>

<p>Question 2) Could my body possibly be calibrated wrong and front focussing the lenses? (I don't have another body to try them on so I'm a bit stuck in that regard..) If not I can just keep on exchanging the 50mm 1.4 until I get one I like..</p>

<p>And finally I did all my focus testing on a sturdy tripod at iso 200, shutter speed approx 125, f/2 (or 2.8 for the zoom) with <a href="../learn/focustest/">Bob Atkin's test scale</a>, so I don't think there is anything wrong with my test results. I repeated them several times.</p>

<p>Thanks for reading and any advice/opinions.</p>

[zml]

<p>Have you tried the micro focus adjustment feature on your camera..? </p>

[Marcus Ian]

<p>It certainly is normal for zooms (especially consumer grade units) to have some focus shift, and that seems w/n reason. Given that the DOF @17mm (10ft subject distance) f2.8 is ~16<strong> times</strong> the DOF @50mm, it's pretty hard to imagine that difference affecting your images (though of course if it were the other way around, it might be a problem)</p>

<p>As far as the 50/1.4 goes, I'm curious if you tried to perform AF microadjustment, and if the range on the camera was adequate to 'fix' the problem?</p>

[PuppyDigs]

<p>Try a couple Canon lenses and repeat your test. While they are not immune to focus issues they tend to need less MA than Sigmas. Luckily the 7D has MA and you can tweak any lens as long as it's within the range of the adjustment. </p>

[jamie_robertson2]

<p>I would like to know how many Sigma 50mm f1.4 lenses actually focus properly straight out of the box. Mine certainly didn't and has got worse to the point where AF micro adjust can't correct it. Another Sigma dud to add to my long list. Sometimes I wonder why I bother buying Sigma gear.</p>

[Marcus Ian]

<p>I've used two that worked outstandingly well. Their use convinced me of their superiority to my EF 50/1.4 especially WO and near - they blow away the EF 50. Since yours has gotten <em>progressively worse</em> though, I'd have to think that either something is wrong w/ the lens, or you've been using it to drive nails (perhaps into the coffin you intend to put all the Sigma lenses you keep buying in ;-) ). Maybe you've dropped it? </p>

<p>Luckily for you, you didn't buy a Canon 50/1.4, so it's still under warranty. So why haven't you sent it in to be fixed?</p>

<p>Even though 90% of what we see on forums is related to problems, it's simply ridiculous to assume that there are <em>only</em> problem lenses. On the other hand, one might reasonably assume that there are <em>only</em> problem photogs ;-)</p>

[robatkinson]

Thanks for the responses. I only took

the first copy of the prime back to

exchange it for another copy a few

days ago so I can just take it back to

the shop... Don't have to deal with

warranty or anything yet. I definitely

haven't dropped or do anything to hurt

the 50mm 1.4, haven't dropped the

zoom either but I dont have to much of

a problem with the focus on that as I

can adjust that to what I want with ma..

 

The prime(s) both the one I have now

and the one I returned both front

focussed so bad that +20 ma doesn't

come close to correcting them. The

one I have now would need +30 or 35

I'm guessing and the one I had before

was just off the scale. So obviously I

will have to return the one I have atm.

The fact that they are both so so badly

front focussing just had me wondering

if there is something messed with my

body?

 

I don't have any canon lenses to put on

and test so I guess I will have to just

keep taking the primes back and see if

I can get one the focusses well or is at

least in the range of MA correction.

And if I go through like five copies of

the sigma prime and still haven't got

one that works I'll assume there is

something wrong with the body's

focussing and send it in for repair?

 

Thoughts?

[jamie_robertson2]

<p>Robert, take my word for it: Sigma = trouble. I very much doubt your problem is the 7D. I have owned the following Sigma lenses:</p>

<p>28-105mm - Aperture stuck after 18 months, lens rendered useless<br>

400mm f5.6 - AF dead on arrival<br>

400mm f5.6 - Aperture stuck after 12 months, lens rendered useless<br>

10-20mm - Good lens, the only Sigma lens that worked well for me (although I only used it occasionally)<br>

12-24mm - Worked reasonably well at first, now image quality is dire in one corner to the point where I have to crop all my images.<br>

50mm f1.4 - AF was out on arrival but +20 in the AF adjust got it back to normal. 2 months later and the AF has somehow moved so +20 is not enough to compensate. Lens needs to go back.</p>

<p>I only own the 12-24mm and the 50mm 1.4 now. The 12-24mm is out of warranty so I'm stuck with yet another paperweight. As soon as the 50mm comes back from Sigma it will be sold. I've completely had it with them. The only good thing about Sigma lenses is the glass in them. Everything else is trash. It wouldn't be so bad if their repair dept even knew how to fix the things.</p>

[robatkinson]

<p>Thanks for the reply Jamie, but I am confident that once I get a good copy of the 50mm it won't break on me.. And besides I have a three year replacement warranty on it, so I dont really mind if it gets busted. I'm not a pro photog so its not going to cost me a job or anything if it stops working down the line..</p>

<p>The assurances on the body are good though. And I'm not seeing a bit of a trend with out of the box issues with the lens. I can just keep exchanging and testing the 50mm until I get a good one. The shop is only down the road so I could keep exchanging it everyday if I wanted to.. I think for the mean time I'll just get another one to test out, the solid built, sharpness, 77mm filter size etc. of the sigma are too nice to pass up easily.</p>