Sigma 10-20mm problem

[hairball]

Hi, all

This is my first post here, but I have been very much enjoying the podcast and i am wondering if you can help me decide if my lens is faulty.

I have recently bought a second hand Sigma 10-20mm EX which are known to occasionally have a soft focus problem on their left sides. well, mine appears to be one of them I'm sorry to say.

I have just created a gallery of pics that are identical but for the aperture and it's here Picasa Web Albums - Steve Hill - Test pictures

I set the camera on a tripod, locked the mirror, waited 6-7 seconds before opening the shutter with a remote, it's windless evening, and i used manual focus.

They're taken in order starting from the largest aperture to the smallest, and I am sure there's a problem but sadly i cannot send it back to Sigma for warranty repair as the warranties are "not transferable". They will repair it, but they want £90! That's a bit much for my taste, but I would really like a lens that is not soft in focus.

Does anyone have any advice or ideas?

Many thanks in advance.

[Marko]

Thanks for the compliment hairball - much appreciated!
In terms of your lens though.....Imo this is a very poor test. It's difficult to see accurate results here because of the plane of focus. Both the camera and the subject need to be perfectly straight and they all need to focus on the same place for all apertures. Here, you are shooting wide angle on an upward angle with a subject that is not flat.

Depending on where you focused for this image it makes perfect sense that the left side WOULD be soft.

I'd redo this test indoors with a newspaper taped on a straight wall and the camera PERFECTLY straight. Focus on text at the center of the viewfinder. This way, the entire subject is in the same plane as the camera which is impossible with the subject you choose. If the left side is soft after this test, you have a bum lens. In my experience, it's rarely the lens though.

Good luck!

marko

[hairball]

Hi, Marko

Nice to hear from you and thanks for the advice. I will now dig out some newspaper and tape and create a new and fairer test.

Thanks again!

[hairball]

I taped newspaper to the wall, centred my lens on the handy printing marks on the paper and shot a few pics with the Sigma and the kit Canon 17-85mm. The latter has come out MUCH sharper across the whole picture. The conditions were the same and I have copied the shots with the same aperture and put them side by side for comparison.

Picasa Web Albums - Steve Hill - Lens test

What do you think?