Sigma 10-20 Focus Issue W/Samples

[form]

I swear this lens is driving me insane. The issue seems to be focus-related. The problem shows up more at 20mm. I've tested it over and over and have never felt right about the performance. This is the one of my three lenses which I feel totally uncomfortable using.

Here's what I keep running into:

• Right side does not seem to focus at the same time as the left and middle.

• I can get the right side focused by setting the lens for a longer focus distance, but at the expense of the left and center.

• I can get the left and center focused by shortening the focus distance, but at the expense of the right.

I would like personal opinions as to what this might be caused by, and I would greatly appreciate any sharing of similar experiences. I currently I have little choice but to send it in to Sigma so they can evaluate it.

Thank You for your assistance.

[MagentaJoe]

Swap your lens for another from your dealer. When built correctly the lens will have none of what you are experiencing. I have the Sigma 10-20 and it's perfectly even across the frame at all focal lengths. You seem to have the same complaint as some others.

[form]

I suppose it's some relief to know it's not an isolated incident. Thanks. I'll have to send it in because I bought it online. Quite literally, I couldn't afford the local stores' ~35% higher price.

[MiG82]

I have heard that this is due to decentred elements, and unfortunately I have it too :(
I haven't had the best experience with Sigma, but it will take much more crap before I hand over twice as much for an equivalent Canon lens.

Edit: Removed "(hey wait, they don't even have an equivalent)". What was I thinking?

[form]

That's exactly what it seems like, the right side being more out of the proper distance relative to other elements than the left. The left and center have a similar, much deeper, more tolerant DOF overall, while the right is blurred almost all the time except in the focus distance "sweet spot"...which shouldn't be the sweet spot, and at which point the left and middle are totally soft.

As I said in another post, I got the chance yesterday to compare the canon 10-22 to my Sigma and the store's, and the center (and whatever side was clear) seemed sharper on the Sigmas.

I'm sorry; have you sent yours in? Mine's well under warranty (2 months old), and was DOA. I'm going to be sending it in as soon as the weekend's over. I don't know about you, but I can't live with, much less afford, $500 defects.

[MiG82]

"I'm sorry; have you sent yours in?"
I haven't got around to it yet because it's not very noticable in my case, but I certainly will because I don't think it's acceptable.

[form]

It's very noticeable in my case. I almost can't believe they let it leave the factory, the way it is.

What I probably should've done in the first place was send it right back to the seller the moment I was dissatisfied with its performance...but I didn't know exactly what the problem was, and even after a few initial tests I still couldn't rule out user error.

I suppose that's what I have to do from now on: Test every lens extensively upon receiving it, and if something's amiss that I can consistently identify and recreate, send it straight back immediately.

I don't think this is the way it should be, having to carefully scrutinize each new lens to make sure it works as well as it's supposed to. That IS technically the manufacturer's duty to consumers, before the product even gets distributed, isn't it? What are we paying for, after all?

Sorry if I'm ranting, but the subject bothers me every time I think about it.