Sigma EX 30mm 1.4 Focus Testing. (advice?)

Hi; I've purchased a used Sigma 30mm.. but I'm not sure it's focusing correctly. ..or I'm not sure it's as sharp as it should be. I'd love any opinions here.

I know shooting at 1.4 gives you a sliver of a DOF.. but have a look here:
(in between each shot, I refocused on something further away before taking the shot)
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I had the same problem.. it looks decentered!

I sent it back to sigma and they could not correct it and gave me a new one.

According to this test, your lens's focus is spot on, but for testing you should really be using non-angled target test charts.

I am missing something or maybe I didn't look closely.

For a fast lens like this one, it's vital that you line up that test chart perfectly. It is not lined up in your test images, so that could contribute to the problem. What's happening here is that your camera is slightly closer to the left mm scale than the right one. As a result the image may be sharp on the left (closer) mm scale but will appear to front focus on the right one (where the 0 point is a bit farther).
But of course decentering can also be part of the problem. It's just that you need to eliminate all variables when testing in order to find out a problem like this.

Shooting these kinds of inclined targets will drive you crazy (it almost happened to me ) - you'll never be 100% sure if it is indeed focusing at the black bar at the center.

My advise is to shoot flat (perpendicular to your line of sight) targets (in bright daylight) using the dot-tune method - very fast and accurate, especially if your camera can run Magic Lantern firmware (dot-tune is already included in nightly release of Magic Lantern).

Put it on the tripod and align the paper.. if that is done well then you should have fairly accurate results.

I had similar results after I tested multiple times.
As you can see its backfocusing on the left and front focusing on the right.

No matter how I aligned the paper the results were the same.
I sent to sigma and they confirmed the lens was decentered.

Shoot real photos. If you notice a problem then do tests in a proper way. Your chart is misaligned. This is why I never recommend lens "testing". People set the test up incorrectly and blame the lens.

Sirrith wrote in post #16046638
Shoot real photos. If you notice a problem then do tests in a proper way. Your chart is misaligned. This is why I never recommend lens "testing". People set the test up incorrectly and blame the lens.

I understand your point but if the lens test is setup correctly and there is a problem why would I wait to find out in "real photos".

It might take months to figure it out and you will always doubt whether its technique, or camera shake, or subject etc... All the while its actually is a decentered lens!

My tests revealed a problem the week the lens arrived... I sent to sigma and they confirmed the problem and now I am shooting with a brand new lens that focuses perfectly!!!

Now when it's poorly done I KNOW it's my fault and can't blame the lens

Lexar wrote in post #16046802
It might take months to figure it out and you will always doubt whether its technique, or camera shake, or subject etc... All the while its actually is a decentered lens!

What I mean is shoot without testing until the moment you get any doubts, then test. If you have no doubts that means your photos are coming out perfectly fine, which precludes any reason for tests! But make sure you know how to test properly

I went nuts trying to use the chart. Your comment about the sliver of DOF was what I kep thinking about. I decided to make lines as simple as possible for the test.

I ended up using 5 AA batts lined up with offset. Put the camera perpendicular to the batts. Multiple shots later, the test showed the Sigma 30mm focused properly.