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05-13-2012, 07:19 PM   #1
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Is my new sigma 8-16 a good copy?

check 100%crop and see what you think
I think it is not as sharp as many review says.
these pic are all took at 8mm and f5.6


Last edited by liukaitc; 06-02-2013 at 12:04 PM.
05-13-2012, 07:38 PM   #2
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Where are you focused on these shots? Focusing is pretty tough with this lens (on distant objects that is), at 5.6 and you are focusing distant then foreground will be oof.

Have you taken a load of shots yet? Are all snaps like this? This is a totally different beast than anything else you have (according to your signature) and it will take some time to get used to. Post a few close-ups shot at 8mm and 5.6...
05-13-2012, 07:50 PM   #3
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focus at far away subject
at 8mm, there is not much worry about DOF.
05-13-2012, 07:52 PM   #4
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That looks more or less normal to me. I've heard that this particular lens could be sharper at the wide end.


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05-13-2012, 08:01 PM   #5
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yeah. seems ok. but not as sharp as many review and people claim
at least I think my 16-50 at 16mm f5.6 is sharper than this (at center)

bought at B&H, so I can always exchange a new one within 1 month.

I will try to shoot more tomorrow to see
05-13-2012, 08:15 PM   #6
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Shoot at f11 and try to focus with live view, just in case...
Then you'll check the optics
05-13-2012, 08:37 PM   #7
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QuoteOriginally posted by liukaitc Quote
there is not much worry about DOF.
Exactly, the DOF is so great that the camera could have focused anywhere within that huge DOF. The concept of DOF and pixel peeping are incompatible. To pixel peep you need to ensure that the focal plane is placed exactly on the object you are peeping at.

In that short of the Play Area, it looks like focal plane was in the red pavers in the foreground just after where the grey concrete meets the red pavers.
05-13-2012, 09:43 PM   #8
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these look decent but i dont know the lens.

05-13-2012, 09:53 PM - 5 Likes   #9
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I am going to comment on the first image and crop. I am going to estimate that the fence posts are about 10' apart, so the distance to the woman sitting on the bench is about 40 feet? At 8mm, with a target range of 40', the field of view is 120' x 80' (see the dimensional calculator at http://www.tawbaware.com/maxlyons/calc.htm). The K5 sensor size is 4928 x 3264, or at that range each pixel is 0.024 feet or about .3 inch. If an average face is (I don't know) 8 inches wide, so that would be 24 pixels. How much facial definition can you get in 24 pixels of width? Not a whole lot of resolution there. Actually in the cropped image you can tell that she is Asian, looks somewhat tired - pretty good resolution for that. Take a look at the gentleman holding the child, and the child's face and hair style. At this distance for a Ultra Wide lens (in a cropped shot) - this is not bad at all in my opinion.

Where I am going here, is that with ultra wide angle lenses, you are pulling in a tremendous amount of additional scenery around the edges and pushing the center back away into the background to accommodate this additional area. So you have a lot more scene, its wide - however you have the same amount of pixels with which to record the scene. Therefore, each pixel will be recording a lot more information than say it would be with using a 30mm lens (normal for a cropped camera).

For the sake of argument, lets use the same scene with a 30mm lens. FoV would be 30' x 21' and each pixel would be ,07 inch, or for an 8 inch face 114 pixels across. This is nearly 5x more definition in just the horizontal axis, or 25 times more resolution in area.

The moral of this is, you are not going to get the resolution you are use to when you have an ultra wide lens mounted. There is that word again - ultra. The resolution and definition are being traded for a tremendous larger scene width and height - scene area. It has to go some where - and where it ends up is in the pixels. It does not mean that the lens is not sharp. You are just using the wrong standard of comparison.

As others have said, where are you focused and what is the aperture, thus your hyperfocal depth of field. I am thinking that the monkey bars might be a tad sharper, but then again it all depends on what you and the camera were focused on.
____________

The last set of images. Lets assume that the sidewalk is creased at 10 foot intervals, so you are about 70 feet from the street sign. In the crop image, you can read the street sign 28 th Ave, also almost able to read the walk/don't walk instructions on the push button and nearly able to see the license plate on the car. [If this was a TV show, I could zoom in again, sharpen, apply a (brand new from the MIT lab, beta version that i just received this morning from my friend) pseudohyperspectral sharpening mask, zoom again and then clearly see the license plate and that the owner is behind in his new registration tags, and parks at the beach since it has seagull poop on it. But this is just a mere plain Jane pedestrian Pentax camera, not an ultra professional Nikon or Canon. (just kidding).] If the focus was anywhere near that plane of focus, you are doing pretty well. How high is the lettering on the street sign? I am going to say what - 4 inches tall? You can almost make out the green sign across the street above the parked car with the license plates.
____________

Now if you are going to really make a comparison, then use the 8-16 at 16mm compared to your 16-50 lens at 16mm. Apples to apples. Then you are going to have to make a slight adjustment since the 8-16 is at the top end of its range, while the 16-50 is at the bottom end of its range. What you don't know is how each lens is optimized within its respective range of focal lengths. Take 2 images, focused on exactly the same point, using the same aperture (f8 should be a good sweet spot for each lens) so that you will have the same depth of field, at the same focus - infinity would probably be best. That, I think will be the best test - with a relative known "good" standard as a benchmark. My guess is, that they are going to be pretty equivalent. Any slight difference could easily be attributed to how each lens was optimized.

Bottom line - I think that the camera lens combination is pretty damm good!!!! (if this is a bad copy, I would like to see what a good copy could do?)



Last edited by interested_observer; 05-13-2012 at 11:25 PM.
05-13-2012, 10:34 PM   #10
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I have a similar problem with the lens
05-14-2012, 12:39 AM - 1 Like   #11
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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.
05-14-2012, 12:45 AM   #12
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QuoteOriginally posted by aneumoin Quote
I have a similar problem with the lens
IMO, it's not the lens' fault. For 'extreme wide landscape' the crop sensor has limitation.
We can improve it with a heavy tripod, mirror lockups, f11, lowest possible iso, and wind still condition.
Sharpening i PP does help a bit.

Bottomline, how often do you enlarge the photos as wall size and view it in 2 feet distance?
05-14-2012, 03:48 AM   #13
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this is a sample from canon 50d.
is that sharper than mine copy?

Last edited by liukaitc; 06-02-2013 at 12:04 PM.
05-14-2012, 03:59 AM   #14
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To answer that question, you need to set the cameras up side by side and take a photo of the same scene at the same settings in the same light.

05-14-2012, 04:04 AM   #15
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Yes and because:
Your photos are at f5.6, shutter speed 1/100, 1/50 and 1/60. iso 80 is not native.
Your friend's photos are taken with 1/500s, f7.1 - i don't know the native iso of the canon 50d.

Still, we are talking about pixel level here, so 1/100s-1/50s does matter.
f8 seems to be the optimal for this lens. Try 1/500s, iso 100/200, turn SR off. I don't think SR will work properly in extreme wide. Hold the camera stable during test shots.
Try first f7.1 as your friend has, same scene/light condition if possible.
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