What's wrong with my lens? :o(

JumboBeef

JumboBeef

Suspended / Banned
Messages
978
Edit My Images
Yes
Here is a photo taken with my 12-24mm Sigma DG HSM. I have been thinking some of shots have been looking soft, particually on the lefthand side, and this looks pants :o(

test.jpg


Hi res here (1Mb).

Canon 40D, 12mm, f/9, 1/125, ISO 100.

What's wrong? :help:
 
Its de-centered.

To confirm, find a flat brickwall and shoot it at f/8. Without re-focusing, turn the camera upside down 180 degrees and re-shoot the same shot.

If the softness "flips" sides from left to right on the upside down image, you have a de-centered lens.

Good luck :)
 
This is a very common problem with this lens...probably the most reported issue with any Sigma lens out there. The good news is that it can be fixed but needs to be sent to Sigma for re-alignment....I've seen reports of free service outside the warranty period too.

HTH

Bob
 
As long as you have a vat paid receipt, Sigma are very good and will turn the repair round quickly. Give them a call.

service@sigma-imaging-uk.com
Telephone: 01707 329999

Postal Address:
Sigma Imaging (UK) Ltd.
13 Little Mundells
Welwyn Garden City
Hertfordshire
AL7 1 EW
 
Thanks!

The lens is UK bought, but it is four and a half years old now. Any idea how much they will charge and how long it will take please?

How does it become de-centred? The lens has never been dropped or bashed.

Thanks again.
 
:runaway:

OK, just had a long chat with Sigma.

They say they doubt it is de-centred. They say it would have to have been like that since new (which it hasn't) or has taken a bash (which it hasn't).

They can only recalibrate the front and back focus (which will cost £33.95) and will take two weeks. If it is de-centred, they will need to send it back to Japan, and it will take eight weeks! I might not see it again until October!

Plus, they have said they would recommend I send the camera body in with it too(!), so they can set the lens up to the body.

I asked them about 10-20. I though maybe I should buy a 10-20 and once this lens retuns, sell it. I always though because this lens is about four and a half years old, the 10-20 would be a better lens. However, they tell me the 12-24 I have is still the current model and at around £600 is 'better' than the 10-20 (around £400) as it can be used on full frame cameras, whereas the 10-20 can't. Is this true?

Anyway, I've taken some more test shots (just snaps, no C+C!)

This was taken this morning on my 40D, f9, 1.125, ISO 100

test3.jpg


Hi res here (1+Mb)

Now with the same lens, but using my wife's 40D body at the same settings (f9, 1/125, ISO 100)

test2.jpg


Hi res here (1+Mb)

Both shots are as they came out of the camera (RAW) and only had a little of sharpening.

It doesn't look as bad now :thinking:

But............

Here is a shot from a set for a client taken a few days ago:

tesco_test.jpg


Hi res here (1+Mb)

....to me, that looks soft on the left again (and it has been cropped, so the worse, the far left, is not there.

What's wrong? What can I do to put it right! :bang:

Arrgghh! :gag:

Thanks!
 
These lenses are known to have that sort of problem. I have sent mine to Sigma for calibration and am still waiting. Mine is 10-20.
Sigma tel 01707 329 999
 
Did you do the brickwall test I suggested further up.

This test is definate to check a de-centered lens.

If you missed my post, its the second one.
 
Okay, here's my take on what's likely to be happening......others may disagree though.

One of the elements in your lens is decentered...the optical centre of the lens is not on the centre axis through the whole assembly. This causes some divergence or convergence of the light resulting in a slightly OOF area somewhere on the sensor. The f/stop used will vary the amount of error and it will not appear in all images due to increased DOF at smaller apertures. Some of the elements will may rotate and if the decentered one does (it normally doesn't) then the OOF area will move with it and may even be outside the area of the sensor (your sensor is wider than tall so the problem is more likely to appear along a side than at the top or bottom of the image).

Can anybody expand on that ?

Bob
 
puddleduck said:
Did you do the brickwall test I suggested further up.

This test is definate to check a de-centered lens.

If you missed my post, its the second one.
Click to expand...

Yes (sorry) I will have a look at doing that tomorrow. One question though........why wouldn't the softness go around with the lens when you turn the camera upsidedown? What does it prove? Surely the softness would flip over, even if it was another issue with the lens, or even the body? :thinking:
 
I haven't been outside to shoot the wall yet but I will shortly *wimp raining smilie*
 
You must log in or register to reply here.
Back
Top