Help is my lens in need of a repair

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smithyt68i

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Craig
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Hello,

I brought a sigma 70-200 2.8 EX apo a few weeks ago and have not been quite sure its focusing properly. I have seen various things about front and back focusing but Im not sure its doing that. im just not really getting the images that i should with this lens, slightly out of focus and not sharp. Any one got any advise ? or am i seriously just not getting the settings right

[url=http://www.flickr.com/photos/craigsmithphoto/5253348137/] Craig Smith Photography-20 by Craig Martin Smith Photography, on Flickr[/URL]

[url=http://www.flickr.com/photos/craigsmithphoto/5253347751/] Craig Smith Photography-2 by Craig Martin Smith Photography, on Flickr[/URL]
 
On what camera, and what settings?
 
sorry forgot that bit,
Nikon D300s
Contiuneus focus
high iso
500/800th
F4
centre focus point
 
So do you think it is rear focusing ? sorry still abit new to this. i will also make the pictures public so the full images can be viewed
 
Number 1:- Unless I'm reading it wrong, the exif shows it is focused at infinity and the ISO is 2500.

Was it in autofocus or manual?
 
Number 2 also shows it at infinity at ISO1250
 
You may have two problems, in the second photo the problem appears to be motion blur if you look at the none moving feet they are quite sharp.

Are you using the Dynamic Area AF 3D tracking option.
 
It is severely backfocusing and there may be two reasons. a) the lens calibration is completely off; b) the photographer accidentally focused on the fence instead of the player due to very fast action.

You should do a test on a static object first to rule out b).

If it is a) then you could try AF micro adjust. If that fails, then back to sigma or to the shop.

A time saving tip: get Nikkor.
 
i tried a few different settings yesterday, as i was getting very frustrated as i was not getting the good results.

I started with 51 3d but then went down the one of the lower options.

The more I look at some of the results from yesterday I think i do have a back focus issue. The back round looks better than the subject. Am I right?

[url=http://www.flickr.com/photos/craigsmithphoto/5254017536/] Craig Smith Photography-20 by Craig Martin Smith Photography, on Flickr[/URL]

[url=http://www.flickr.com/photos/craigsmithphoto/5254017250/] Craig Smith Photography-19 by Craig Martin Smith Photography, on Flickr[/URL]
 
An easy way to check for back focusing is to put the camera on a tripod and take a photograph using the center focus spot. Then take the same photo using live view on the same spot and compare the images. The live view uses contrast detection whereby it just adjust the focus until it sees a sharp image.

Ideally both images should be focused on the same point if not mess about with the AF fine tune. Although I have never found it that effective on zooms as there seam a bit inconsistent throughout the zoom range.
 
If you're using the 51-point 3D tracking it could well be that the camera has simply "jumped" over and locked onto to the higher contrast between the window and the white panel.
 
Go and take a photo of something static but with lots of sharpness, eg a brick wall using your centre af point. Take the photo at a 45 degree angle with an obvious marker in the middle, something like an easily distinguishable crack or a chalk mark. If that comes back pin sharp in the centre then its not back focussing.

The speed of focussing with your camera means that with action pics, as soon as your subject moves off centre you'll focus on the background, like might have happened on the shots you posted
 
IMHO, internet forums are far too hasty to see the word Sigma and pronounce some kind of lens error.

It can happen, but actually not very often and Sigma are pretty good at fixing it. Much more often, it is user error and in this case the evidence for that is strong. The lens appears to missing the subject focus, or rather the camera is. The lens will only focus on what the camera/user tells it to.
 
daugirdas said:
It is severely backfocusing and there may be two reasons. a) the lens calibration is completely off; b) the photographer accidentally focused on the fence instead of the player due to very fast action.

You should do a test on a static object first to rule out b).

If it is a) then you could try AF micro adjust. If that fails, then back to sigma or to the shop.

A time saving tip: get Nikkor.
Click to expand...

Gosh, a thread about a sigma lens, where yet again you slate them, no supprise, but at least here is a suggestion it may be user error

smithyt68i said:
i tried a few different settings yesterday, as i was getting very frustrated as i was not getting the good results.

I started with 51 3d but then went down the one of the lower options.

The more I look at some of the results from yesterday I think i do have a back focus issue. The back round looks better than the subject. Am I right?

[url=http://www.flickr.com/photos/craigsmithphoto/5254017536/] Craig Smith Photography-20 by Craig Martin Smith Photography, on Flickr[/URL]

[url=http://www.flickr.com/photos/craigsmithphoto/5254017250/] Craig Smith Photography-19 by Craig Martin Smith Photography, on Flickr[/URL]
Click to expand...

One of the settings on the d300 and d300s is for continuous focus lock delay time, meaning if you are using a set focus point, you can set a delay before the camera refocuses on a new subject if it picks a new subjerct up

HoppyUK said:
IMHO, internet forums are far too hasty to see the word Sigma and pronounce some kind of lens error.

It can happen, but actually not very often and Sigma are pretty good at fixing it. Much more often, it is user error and in this case the evidence for that is strong. The lens appears to missing the subject focus, or rather the camera is. The lens will only focus on what the camera/user tells it to.
Click to expand...

Absolutely agree with you.
 
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