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04-06-2014, 03:37 PM   #1
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DA* 16-50mm: rather crappy sharpness outside of centre

Hi everyone!

I went to a formation dancing tournament yesterday with the said lens that I borrowed from my dealer. It's a pretty pricey lens and I wasn't sure if the focal lengths would be ok for what I wanted to shoot. I was especially worried about the long end of the zoom range because the subjects I wanted to shoot are sometimes 10 to 15m away from me (and I am not allowed any closer). I never suspected I'd have a problem with the image quality!

After the tournament I took a group photo. Noone was moving around, the girls were actually sitting down. This is the photo I am talking about:

http://media.advico.de/photo/misc/hilden_group_2.jpg

It has full resolution, no copping was done and no post-processing in terms of sharpness. I did lift the colours up a bit. The EXIF info is still there, so you can see it was shot with a K-3, f/4, 1s/180, 26mm focal length (absolute). I used a Metz 58 AF-2 in P-TTL mode with a small mobile softbox over the flash. The flash was set to the widest possible angle - normal when it is stuck into a softbox. The camera focussed onto one of the girls in the middle of the photo.

Take a look at the row of girls. They are sharp in the middle. I know that most zoom lenses aren't that great at the edges (which is why I stopped down to f/4) but what this lens offers especially on the right side is absolutely hideous! Really weird is the difference between left and right. The left side seems a bit on the soft side (which I find a bit less than thrilling considering the price of the lens) but the right side is really gruesome. Not only this photo has this effect, not all, but many. The reason I wanted to try out this lens was because I found the softness of my kit lens (18-135mm) around the corners annoying. However, I can't remember a single photo shot with my kit lens being anywhere near as bad as this.

Am I too dumb to operate a camera? Is the lens broken? Or is this a problem with the shake reduction?

Kind regards,
Chris

04-06-2014, 03:43 PM   #2
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Well assuming you weren't holding the camera slightly off angle it sounds like a decentered lens. I am sure if you got a properly calibrated lens it would be sharp shooting at F4.

Note that at F4 if people should not be in the same focal plane there is still enough shallow depth of field for all the people not to be in focus.

Howie B
04-06-2014, 04:02 PM   #3
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It's very obvious, you're right about that. My immediate thought is that the girls on the right are beyond the DOF area that would be in focus relative to your position while the people in front are. The people in the right rear are well into bokeh territory while the last 3 people on the right gradually get out of focus. I think you should have stopped down a little more. Subjects on the edges of a shot are further away than those in front so you have to figure that in when you choose an F stop.
04-06-2014, 04:02 PM   #4
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There is definitely a problem with the lens. The hyperfocal at f/4 on APS-C with a 26mm lens is about 8.5m. Your subjects appear to be about 10 meters away with point of focus looking to be the knees of the women at center. At 10 meters the near focus should be about 4.5 meters with far focus at infinity. There should be plenty of DOF at moderate magnification (say computer display), but the edges are not just OOF, they are visibly "smeared". Are you able to do a controlled test with the lens or have you already taken it back? Any possibility there was goo on the rear element?


Steve


Last edited by stevebrot; 04-06-2014 at 04:08 PM.
04-06-2014, 05:08 PM   #5
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Wow that looks really bad. My DA*16-50 is evenly sharp at F4. Must be a problem with that lens.
04-06-2014, 05:26 PM   #6
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Well as a comparison, here is a test photo of a wide fence at maybe a similar distance with the ordinary 18 ~ 55mm at f/5.6 and 40mm.
https://app.box.com/s/b051d299249fd47b1b1e
Not perfect but much better that your photo
Notice that on your photo, the floor in foreground is sharply focussed whereas in my test image, the grass in the foreground show the normal blur by near dof.

So I wonder if your lens has an angular misalignment, maybe it has been dropped?
04-06-2014, 05:39 PM   #7
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yup, right side is a lot softer than the left side. very unusual. do some controlled tests of objects hanging on the wall or brick walls.
04-07-2014, 06:22 AM   #8
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QuoteOriginally posted by PixelGeek Quote
Hi everyone!

I went to a formation dancing tournament yesterday with the said lens that I borrowed from my dealer. It's a pretty pricey lens and I wasn't sure if the focal lengths would be ok for what I wanted to shoot. I was especially worried about the long end of the zoom range because the subjects I wanted to shoot are sometimes 10 to 15m away from me (and I am not allowed any closer). I never suspected I'd have a problem with the image quality!

After the tournament I took a group photo. Noone was moving around, the girls were actually sitting down. This is the photo I am talking about:

http://media.advico.de/photo/misc/hilden_group_2.jpg

It has full resolution, no copping was done and no post-processing in terms of sharpness. I did lift the colours up a bit. The EXIF info is still there, so you can see it was shot with a K-3, f/4, 1s/180, 26mm focal length (absolute). I used a Metz 58 AF-2 in P-TTL mode with a small mobile softbox over the flash. The flash was set to the widest possible angle - normal when it is stuck into a softbox. The camera focussed onto one of the girls in the middle of the photo.

Take a look at the row of girls. They are sharp in the middle. I know that most zoom lenses aren't that great at the edges (which is why I stopped down to f/4) but what this lens offers especially on the right side is absolutely hideous! Really weird is the difference between left and right. The left side seems a bit on the soft side (which I find a bit less than thrilling considering the price of the lens) but the right side is really gruesome. Not only this photo has this effect, not all, but many. The reason I wanted to try out this lens was because I found the softness of my kit lens (18-135mm) around the corners annoying. However, I can't remember a single photo shot with my kit lens being anywhere near as bad as this.

Am I too dumb to operate a camera? Is the lens broken? Or is this a problem with the shake reduction?

Kind regards,
Chris
Given there is a clear double image on the right hand side (see pearly earrings) I'd be surprised if a lens issue (as in decenter-ed) was to blame

The image looks for all the world like 'rotated' with shutter press but if it is a lens problem then would have to be a loose internal element, was this a heavily used 'demo' copy.?

Either way it not normal for this lens.

04-07-2014, 06:44 AM   #9
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This definitely should be the sweet spot for this lens and should be sharp wide open, edge to edge. Certainly at f4 you shouldn't see blurring. I would shoot a brick wall at various focal lengths on a tripod just to be sure -- it should be pretty clear, particularly at the wider end of the zoom.
04-07-2014, 09:44 AM   #10
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QuoteOriginally posted by awaldram Quote
The image looks for all the world like 'rotated' with shutter press
There is evidence in the shot of some rotational movement if you compare the sequins of the guy at far left with the guy at far right. I don't believe that would explain the overall weakness of right side though.


Steve
04-07-2014, 09:58 AM   #11
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QuoteOriginally posted by stevebrot Quote
I don't believe that would explain the overall weakness of right side though.
Nor the quite sharp floor tiles close in on the lower of the image
04-07-2014, 01:04 PM   #12
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Original Poster
Hey everyone!

Thanks for your thoughts!

Just to make it clear: I was holding the camera in my hand (no tripod anywhere to be seen), but this was a pretty wide angle and the shutter speed was at 1s/180. There should not be any visible movement due to an unsteady hand.

I found a photo that shows the effect even better:
http://media.advico.de/photo/misc/blurrrrr.jpg

Note the dude in the middle. You can see the cord on his blazer. But the guy on the far right seems to be getting ahead of himself (get a load of his chin!). If there is any blurring due to camera shake, it should be in the other direction.

Regards,
Chris
04-07-2014, 03:17 PM   #13
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QuoteOriginally posted by PixelGeek Quote
But the guy on the far right seems to be getting ahead of himself (get a load of his chin!).
I am not sure you can rule out subject motion here. The appearance is pretty much textbook ambient light ghosting.

If it were me, before pinning the blame on the lens I would do a controlled test, on tripod and without flash, of a stationary subject. The intent is to remove all variables that could be contributing to the softness issue. I would also carefully examine the rear element. Something tells me there is a smear of grease or a fingerprint on the side.

Assuming you have already returned the lens to the dealer, did you mention the problems you encountered?


Steve
04-08-2014, 01:20 AM   #14
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Bonjour!

I have my doubts about the ambient light ghosting, for three reasons:

1. It's only ever on the right side of the frame, never on the left and never in the middle. I shot 425 photos that Saturday, so I think there is enough material for a statistic evaluation.

2. I habbitually test out what settings I would need to be able to shoot without a flash. On this day I was at about f/2.8, 1s/50, ISO400. The shot was made with 1s/180 and f/4. The ghosting is just too bright for the ambient light IMHO and also far to wide considering the exposure time.

3. I never encountered this with the kit lens (18-135mm) and I've used that several times already for this kind of shoot.

The lens is still at my place. I had one of these 12 hour workdays yesterday - the kind we all love so very much. It was far too late to bring the lens anywhere by the time I got home. And since it was dark, I couldn't shoot any test photos either. What I could do was look at the lense very carefully under a light. I saw no signs of smudges, fingerprints or anything else on both the front or the rear element.

I will try to leave the office before 6 today and thus maybe still have some daylight when I come home, and if it's not raining, I'll take some photos of houses and walls.

Regards,
Chris
04-08-2014, 11:02 AM   #15
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QuoteOriginally posted by PixelGeek Quote
I will try to leave the office before 6 today and thus maybe still have some daylight when I come home, and if it's not raining, I'll take some photos of houses and walls.
Cool! I will be curious to see your results. The shopkeeper will probably also be thankful.


Steve
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