A few questions for Sigma 12-24 EX owners

I have been shooting with someone else's Sigma 12-24 EX for a few days now, and which I could buy if I wanted to.

I have been looking at tests of this lens on FF, and it looks like it is best at its long end. It also seems that you need to stop down to F/8 or F/11 to get reasonable results in the corners. Furthermore, even at F/11 there still is a lot of vignetting.

From my tests so far this all seems to be the case indeed. Best at 24 mm, a lot of vignetting even at F/11, but worst of all the extreme corners. You can see a marked fall-off in sharpness in the last 15 % or so of the corners, especially at the short end. This sharpness fall-off seems to be more or less the same in each corner.

My question is whether this is really normal, or whether this lens may need calibration?

Furthermore, due to the vignetting, there is a lot more noise in the corners than there is in the centre. How do you deal with this?

Thanks in advance for your replies!

Kind regards, Wim

Wim,

I believe a calibration may help, but ultimately part of the darkening of corners (which I don't classify as vignetting as I would from a hood being improper for the design) comes from the way the front element recedes (slightly) into the barrel as you zoom in to the 24mm end. (I only noticed this myself for the first time a few months ago, after having the lens for more than 1 year at the time... just play with the zoom ring while looking at the lens from the outside and you'll see what I'm talking about). The way the front element is recessed into the barrel like it is I believe factors into those darkened corners.

Also the unique shape of that front element ultimately has something to do with the edge and corner performance.

I could be wrong tho.

I like the lens for the exagerated effect, to me corner-to-corner sharpness isn't a major concern as I'm not using it to shoot landscapes.

Hi Alan,

nureality wrote in post #8505497
Wim,

I believe a calibration may help, but ultimately part of the darkening of corners (which I don't classify as vignetting as I would from a hood being improper for the design) comes from the way the front element recedes (slightly) into the barrel as you zoom in to the 24mm end. (I only noticed this myself for the first time a few months ago, after having the lens for more than 1 year at the time... just play with the zoom ring while looking at the lens from the outside and you'll see what I'm talking about). The way the front element is recessed into the barrel like it is I believe factors into those darkened corners.

Indeed it does, just checked. However, vignetting is less at 24 mm; it is worst at 12 mm. I guess that since the AOV diminishes from 122 to 84 degrees when zooming from 12 to 24 mm this has only very little effect. The hood design is an interesting thought, however, as I noticed, when shooting a whitewashed wall, that the short edges show almost straight bands of vignetting - this could well be caused by the two short ends of the tulip-shaped hood to be a little too long for the 12 mm end. Interesting. More shooting required .

It is supposed to make corner and edge performance better, AFAIK. This is why Nikon designs their shorter FF zooms like this too, and Canon the 14L and TS-E 17 .

Ok, I understand. Can you confirm however that the (extreme) corners are significantly less sharp?

TIA!

Kind regards, Wim