[interested_observer]

Morning, The difference in sharpness between your images and your friend's images are difficult to compare due to the difference in subject matter and composition. The latest sample - the 5D is taken at noon, look at the sun angle, i.e., shadows, is in a constrained space, with lots of linear lines and squares, very contrasty, the eye knows what to expect and helps with the definition. Where as yours is very deep, almost infinitely deep. A great deal of foliage, that with a slight breeze will move, and its shape is difficult for the eye to predict, thus it is not going to aid in clearly making out defined shapes. Between the two sets of scenes - apples and oranges in the determination of "sharpness".

[liukaitc]

OMG!! I find the problem of my copy.
I know there is something not right with the sharpness.
it is about focus. the focus can pass infinity...when I pull it right on infinity. it is super sharp. but when doing autofocus, it pass inifinity. and resoulution decrease.
sorry, my English is not good.
I will post photo soon.

[liukaitc]

OK, here it is. Now I think everyone can understand the issue now.

when doing autofocus, the focus scale pass infinity(can do it manually too), and the resolution decrese.
but when I manually pull it right on infinity, the resolution is superb.

[joe.penn]

Fine tune AF with a +10 and see what happens. You can send it to sigma and they will calibrate it but you need to send the lens plus the camera body...

[Macario]

The lens looks fine to me.
You may asking too much from the lens and the sensor. Note that these 100% are at pixel level.

Yep, you are asking way too much. SHoot at an opbject that is only a meter away or so, and you will that it is very sharp. You cannot expext a wide angle lens to be super sharp on objects in the distance ( an for wide angle, that is already a few meters away)

[liukaitc]

Yep, you are asking way too much. SHoot at an opbject that is only a meter away or so, and you will that it is very sharp. You cannot expext a wide angle lens to be super sharp on objects in the distance ( an for wide angle, that is already a few meters away)

that is because you do not know how sharp this lens is
this lens is consider one of the best zoom lens on the market regarding resolution by some review.
when I manually put focus dsitance scale right at infinity. it is super sharp. you can clearly see all the detail all the way far away
but when I do auto focus. I do not know why the focus dsitance scale pass the infinity indicator. and the resolution drop quite a lot.
Is that the problem of the lens or the camera?
it should stop right on the infinity indicator line. why it pass that?

[liukaitc]

Fine tune AF with a +10 and see what happens. You can send it to sigma and they will calibrate it but you need to send the lens plus the camera body...

thanks, after +10 adjustment. It is fine now.
is that possible to get a copy that does not need AF adjustment?

[joe.penn]

thanks, after +10 adjustment. It is fine now.
is that possible to get a copy that does not need AF adjustment?

Not sure, can't really answer that - I do know that Sigma will calibrate the lens to your camera body, you would however have to send the camera body to Sigma along with the lens.

[hoanpham]

As far as i know, some lenses allow focus pass infinity, just to be sure for shooting condition in the extremes.
I shoot at -20 Celsius for days, and during the Houston summer. AF in camera should spot on.
Try AF adjustment in the K5, if not ok, send the lens back and get the new one.
My first copy has dead AF motor after a day, but i manage to test the lens manually, and finally send it back to get a new one instead of just cancel the buy.

In my experience, Sigma lenses has the highest rate of bad quality control. I have 3 AF sigmas, and have to return 2 of them.
Sigma also allows selling gray copies and the seller will stand alone for the guarantee, not by sigma world-wide.
Gray copies are cheaper, about 70-100 usd cheaper, but personally, I prefer world wide and longer guarantee if possible.

[liukaitc]

As far as i know, some lenses allow focus pass infinity, just to be sure for shooting condition in the extremes.
I shoot at -20 Celsius for days, and during the Houston summer. AF in camera should spot on.
Try AF adjustment in the K5, if not ok, send the lens back and get the new one.
My first copy has dead AF motor after a day, but i manage to test the lens manually, and finally send it back to get a new one instead of just cancel the buy.

In my experience, Sigma lenses has the highest rate of bad quality control. I have 3 AF sigmas, and have to return 2 of them.
Sigma also allows selling gray copies and the seller will stand alone for the guarantee, not by sigma world-wide.
Gray copies are cheaper, about 70-100 usd cheaper, but personally, I prefer world wide and longer guarantee if possible.

Yeah.now I know it is kind frustrated.
but we all know sigma lens has the best value.
if pentax make a 8-16 that is as sharp as the sigma one.
I am pretty sure it will be price over 1000.

[lesmore49]

Either the Canon or Pentax example do not seem sharp.

I thought long and hard about getting the Sigma 10-20 F 4....finally got the Pentax 12-24mm. The 12-24 is very sharp. I'm very happy with it. Expensive in Canada though.

[joe.penn]

The 8~16 is blistering sharp with incredible resolution, great build quality and comes with a great warranty - really can't go wrong with it...

[civiletti]

If you want to guage resolution, use a tripod and static subject. At that magnification motion and focus are critical, even at 8mm.

According to PhotoZone tests, the 8-16 is sharpest at 8mm. I find mine quite sharp, though I use 11-16 most of time to suit my subjects.

[chesebert]

thanks, after +10 adjustment. It is fine now.
is that possible to get a copy that does not need AF adjustment?

Yes. My first 17-70 did the same thing; the exchanged one is on the dot.

[interested_observer]

I am just asking some questions here - inquiring minds and all of that....

• Does the K5 AF well with other lenses?
• Is the problem just localized to only the 8-16?
• You might want to take you camera to B&H with you for the exchange and test the new one on the spot.