# Lens issue or user issue?



## Lizzytish (Jun 24, 2015)

Hey guys. So I bought a used Nikon 610 and a Sigma 70-200 2.8 lens and I am having some issues with it focusing. I am not sure if it's user related or the lens has some issues on its focus point. I also tried out my other Nikkor lens to make sure there wasn't any issues with the body. Just to clarify, I cropped out most of my room because it was a disaster and for you guys to better view my focusing issue.

Here is the camera at 2.8 zoomed to 185mm and the focus point is on the bolt. Focuses just fine.






Now here I am in the same location but with the lens at 70mm at 2.8 and it's focusing about 10 to 12 inches behind the focus point (the bolt). 




Why is this happening? Is it something I am doing wrong or does this seem to be a lens issue? I noticed it happening when I was out shooting a horse show and I would have my focus set somewhere on the horses face with my f stop at different values. Somewhere farther along in the background would be in focus rather than where my focus point would be set regardless if I zoomed in to my subject or had it set at 70. Please help. I need to know what I am doing wrong or if I need to send the lens back.

Also, please be nice. No A-hole comments pretty please. If you have nothing nice to say, don't say it at all.


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## Derrel (Jun 24, 2015)

The shorter the focal length, the more physical area the AF brackets cover. With a cross-type sensor that actually has a "+" shape, the actual focus sensing area can easily extend ABOVE the small focusing square. The actual focusing areas in many cameras extend beyond the AF squares. This is just one shot...and we do not have all the information needed to really diagnose this...you said "same location", but the image sizes are very different. You are close to the paper it seems: what is the minimum focusing distance of the lens?

Second: can you mentally envision where the AF bracket in use was when the 70mm shot  was made? ANd can you literally SEE the in-focus subject matter that the focusing area locked onto? Can you try to, in real time, at the scene, literally AIM the camera and SEE where it focuses, using your eye--and from that, deduce exactly where the actual focusing "area" is, in relation to the AF square?

Focus issues can be a big problem, and Sigma has had many of them; they have to reverse-engineer to make lenses that work with both Canon and Nikon cameras; focus issues can arise whenever a new camera that uses new protocols is developed.

More info would help. What focus mode (AF-S?)? Single-point? Actual distance, etc.


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## Lizzytish (Jun 24, 2015)

It is on AF-S. I was sitting a good 5-6 feet away from the paper and shot at 185mm and then at 70mm. I just cropped out the rest so you could see what was happening. I can manually set my focus point (obviously) which I did but I kept the focus point in the exact same location and focused on the bolt both times.


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## Derrel (Jun 24, 2015)

I typed in Sigma 70-200 f/2.8 specifications, and clicked on a review Sigma 70-200mm f 2.8 EX DG HSM II Macro Lens Review

In the review, the author noted that the first review copy he received had a foreign object inside the lens, and so he sent it back and was sent a second review lens, and it has such severe front-focusing that he sent it back, and was sent a third Sigma 70-200, and it too was defective. As he wrote:

"I was very disappointed to yet receive *another front-focusing copy* of the Sigma 70-200 DG II on my*third attempt*. Two of these lenses came from B&H and a third came from Amazon.com (just to mix things up). I tested these lenses on two Canon EOS 1Ds Mark III bodies (one is Canon-calibrated) and a Canon EOS 40D body. All delivered the same AF results - consistently front-focusing. I don't plan to try a fourth copy."

"The Sigma 70-200mm f/2.8 EX DG HSM II Macro Lens is *well built* - Sigma EX lenses generally are. The focus and zoom rings are nicely sized and relatively smooth-functioning with a nice amount of friction. My third copy of this lens has a little play in the MF ring, but the second was one of the nicer manual focusing lenses I've used."

-----Read the review...there's a consistent mis-focusing issue with the newest 70-200/2.8 II, the one released initially in 2007. There's plenty of sample-to-sample lens variability problems.

Here's another test: the lens focus testing chart and bolt you have allows the camera to focus on whatever distance the AF SENSING area locks onto; the AF sensing area is NOT necessarily the area of the AF bracket in use--there can be,and often is, a larger area that the AF sensing system actually uses. To cross check...how well does the lens focus close-up on a FLAT subject,with one depth plane? That's another test that would give another bit of performance data to evaluate things with.

Maybe the lens can have its focusing micro-adjusted at the 70mm setting?


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## Dave442 (Jun 24, 2015)

I agree to try the flat-test as well.  

Also, I installed a plug-in for LR called Show Focus Point. That shows the point used and if focus was locked and such. It also gives the focus distance and that could be useful as you could physically measure the distance from the sensor plane to the object and compare with the camera data (just down to cm so not that exact).


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