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05-08-2014, 01:17 PM   #1
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K3 with Sigma 17-70

Hi folks,

I've been shooting with a Sigma 17-70 as my primary walk-around lens for several years now. I've used it with a K10, K-7, K-5, and now, my K-3. It's only since I've started noticing significant image degradation on the edges of some images. I'm not a pixel peeper at all, but I've been seeing an unacceptable amount of blurring.

So what is happening here? Are the optics of the lens simply not good enough to keep up with the K-3? Is is possible it has sustained damage?

Attached is an example. It was shot at f7.1, 1/1000, 34mm.

Thanks for looking.

Attached Images
View Picture EXIF
PENTAX K-3  Photo 
05-08-2014, 01:32 PM   #2
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Was this bracketed per exif? That might have something to do with it.
05-08-2014, 01:47 PM   #3
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I always take two bracketed shots. One at regular EV and one under-exposed. Been doing this for years, so I don't believe it to be the source of the problem.
05-08-2014, 02:06 PM   #4
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Are you talking about the right side It seems a lot worse then the left side at a farther distance? I wonder if maybe your lens has become decentered or its severely back focusing.

05-08-2014, 02:16 PM   #5
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I found the Sigma quality check to be problematic. I had to swap THREE times to get an acceptable copy of my 17-70. And even then it's never sharp until f11 especially near the edges. Recently I took a shot of a mountain and submitted it for review in PEG. It was quite embarassing when almost everyone noticed that it was unsharp. I shot it at f8 on a tripod which caused really ugly smudging of the edges and corners.

Check your copy. Compare at f5.6, f8 and f11.
05-08-2014, 02:34 PM   #6
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Yeah, the right side is way worse than the left. I'm pretty sure this is a new phenomenon. I hadn't had problems in the 6 or 7 years previous.

dtmateojr: I will do that test you suggested.
Oldbayrunner: If the lens has become decentered, is this something that can be fixed?
05-08-2014, 04:17 PM   #7
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QuoteOriginally posted by slowdive101 Quote
Yeah, the right side is way worse than the left. I'm pretty sure this is a new phenomenon. I hadn't had problems in the 6 or 7 years previous.

dtmateojr: I will do that test you suggested.
Oldbayrunner: If the lens has become decentered, is this something that can be fixed?
Yes, you would need to send it to a repair center to have the lens elements re-aligned. I would call and tell them what the problem is and get an estimate first. If you send it in send copies of the photos also.
05-08-2014, 06:40 PM   #8
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QuoteOriginally posted by slowdive101 Quote
Hi folks,

I've been shooting with a Sigma 17-70 as my primary walk-around lens for several years now. I've used it with a K10, K-7, K-5, and now, my K-3. It's only since I've started noticing significant image degradation on the edges of some images. I'm not a pixel peeper at all, but I've been seeing an unacceptable amount of blurring.

So what is happening here? Are the optics of the lens simply not good enough to keep up with the K-3? Is is possible it has sustained damage?

Attached is an example. It was shot at f7.1, 1/1000, 34mm.

Thanks for looking.


I went through this years ago with a Sigma 17-70mm f/2.8-4.5 macro. It was softer on one side of the frame versus the other at 17mm f/2.8. That was with my K10D (really Samsung GX10). Sigma got tired of me sending them the lens and asked for my camera I sent it. They took two pics that show slight softness with my GX10 but not with their K10D. But I was not convinced you see all my other two or three lens were fine. How can my body AF need tuning if my other lens are great! Long story short -


I was very wrong. I still have that lens and its great. Its my go to when I am serious shooting, people, landscape, walk around and it fills that role with tack sharp pics even good pics at 17mm f/2.8.


I realize your making a 50% jump in resolution but DXO does not show a drop in the corners with the old Sigma lens. As it was one of the sharpest of the series.


A link to a guy who can test more cameras and lens then most -
LensRentals.com - Notes on Lens and Camera Variation


I strongly recommend auto-focus be checked on your K-3 with the Sigma and one other lens. If you want to send your lens to Sigma up to you. But do have Pentax check the body! Then from there you will know what is going on and can make the next move without guessing.

05-08-2014, 08:29 PM   #9
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I thought I'd post a few more photos for anyone who wants to see. The first two are taken with the 17-70 and show definitive blurring on the right edge. But the third photo (Union Storage) does not show the blurring. Why? Meanwhile, the fourth photo was taken with my Sigma 8-16, and it's tack sharp. This implies it's the lens—not the camera.

To make matters more complicated, I took dtmateojr's suggestion and did comparison test shots at f5.6, f8 and f11. The differences were negligible. In fact, I could not re-create the blurring in these test shots. This implies that the problem is user-generated. But I just don't see how that could be the case. The examples above are taken in good light at fast shutter speeds. I've been doing this for many years, and I don't see how I could all of a sudden have forgotten how to take clear photos.

Perhaps, as jamesm007 suggested, some diagnostics on the camera are in order.
05-08-2014, 08:34 PM   #10
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These two photos were taken with the 17-70 and show the clear blurring on the right.
Attached Images
View Picture EXIF
PENTAX K-3  Photo 
View Picture EXIF
PENTAX K-3  Photo 

Last edited by slowdive101; 05-09-2014 at 07:50 AM.
05-08-2014, 08:36 PM   #11
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These photos do not show blurring. First photo was taken with the 17-70, but there is no apparent blurring.
Second photo, just for comparison, was taken with an 8-16 and is tack-sharp.
Attached Images
View Picture EXIF
PENTAX K-3  Photo 
View Picture EXIF
PENTAX K-3  Photo 

Last edited by slowdive101; 05-09-2014 at 07:51 AM.
05-09-2014, 06:01 AM   #12
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The first set I am still picking up the same difference. The second set I am not.
05-09-2014, 06:45 AM   #13
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Yes, sorry, I had mentioned in the post above the photos that the first set shows the blurring. The second set do not however. The first photo in the second set was also taken with the 17-70. So why does this one not have the blurring? There seems to be some inconsistency, which makes me wonder if the problem is human error (ie—something I'm doing wrong). The second photo in the second set was taken with an 8-16mm and is tack sharp.

The bottom line is that I'm really finding it difficult to get to the bottom of this. It seems like the lens is the problem—not the camera—but then why are some photos taken with that lens sharp?
05-09-2014, 08:15 AM   #14
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My bad I spaced on your post and more looked at the photos....LOL Like yours lens prior, I have none of this with my 17-70mm DC. I am still in the mindset somehow the lens got knocked out of alignment. When have you ever noticed through operator error a photo show one side at approximately the same distance be more blurred then on the other. This does happen with lenses that are showing signs of , possibly in your case, the front element being tilted .

read this;
LensRentals.com - Testing for a Decentered Lens: an Old Technique Gets a Makeover
05-09-2014, 11:11 AM   #15
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I'm going to take the lens in for diagnostics. I hope the repair isn't too costly!
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