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10-28-2014, 04:21 PM   #1
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Is this normal for the 18-55 WR?

I got a flea in one ear about it in another thread, so I'm asking here...
18-55 WR on a K-01, bad picture quality at close range, is my lens a dud or is this normal performance?

Downscaled image (16->6MP), for scale & position of the detail in the frame:


A 100% crop, maximum quality jpeg:


I don't believe that halo should be there (top left) at all, not at f/5.6.
Maybe it's just the "macro" (read "marketing") focusing range that's to blame?
Thanks in advance

10-28-2014, 04:25 PM - 1 Like   #2
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Do you have lens corrections enabled? Sometimes the aberration correction option can introduce unwanted artifacts. The photo looks fine otherwise.

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10-28-2014, 04:33 PM - 1 Like   #3
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Damn, if this had come up a couple months ago, I could have taken a very similar shot.

I'll try to find something that approximates this and post it tomorrow.
10-28-2014, 04:35 PM - 1 Like   #4
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I had the previous version with a slightly different optical formula, but yeah they do tend to be a bit soft at 55mm and it is quite possible that close-focusing is worst -- stop down to f/8 or f/11. DOF is pretty thin there even at f/5.6 if you are close. It is little soft, but it hardly looks terrible...

10-28-2014, 04:40 PM   #5
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QuoteOriginally posted by Adam Quote
Do you have lens corrections enabled? Sometimes the aberration correction option can introduce unwanted artifacts. The photo looks fine otherwise.
Sorry, should have said it...
RAW, minimal PP, now I notice that the correction of chromatic aberrations modifies the look of the halo, but by an insignificant amount.

QuoteOriginally posted by vonBaloney Quote
I had the previous version with a slightly different optical formula, but yeah they do tend to be a bit soft at 55mm and it is quite possible that close-focusing is worst -- stop down to f/8 or f/11. DOF is pretty thin there even at f/5.6 if you are close. It is little soft, but it hardly looks terrible...
Ok, relieved to hear that...
In my experience a 50mm on the K-01 will be noticeably softer at f/8 than at f/5.6 due to diffraction, on a test chart at least...
As for thin DoF, I think focus was ok, and would not blame it for softness.

Thanks all for the prompt responses, posts upvoted.
10-28-2014, 06:13 PM - 1 Like   #6
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Yep, that looks about right. The 18-55 is an excellent 20-40 and a pretty poor 18-20 and 40-55. Both these ranges improve dramatically stopped down by 2/3 or 1 full stop.
The 18-55 performs best at about 35mm - notice the lens is at it's shortest extension at 35 and longest at 18 and 55. I think the lens is optimised for mid focal length.

The 18-135 is a lot better...
10-28-2014, 07:08 PM - 1 Like   #7
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Are you sure about your focus point?

The 18-55 is soft at 55mm, but it appears that the focus point may be behind this particular flower.

BTW...you should probably upload high quality JPEGs (zero compression) rather than a compressed image.


Steve
10-28-2014, 07:12 PM - 1 Like   #8
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Stop this lens down to f9 on sunny days, use at around 35mm for best results.

10-28-2014, 08:26 PM - 1 Like   #9
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I've seen this halo in wide open photos of kit lens! nothing unusual to me. just stop it down to f/8!
10-29-2014, 02:55 AM   #10
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QuoteOriginally posted by stevebrot Quote
Are you sure about your focus point?
The 18-55 is soft at 55mm, but it appears that the focus point may be behind this particular flower.
I believe the stamen and the lower-left petal are dead in focus... even if they are a soft mess...

QuoteOriginally posted by stevebrot Quote
BTW...you should probably upload high quality JPEGs (zero compression) rather than a compressed image.
Steve
The 100% crop is full quality, as stated. The other was just to give you a feel for how close/far to the corners/center was the flower, and there's a 1MB limit on images for me.


QuoteOriginally posted by calsan Quote
Both these ranges improve dramatically stopped down by 2/3 or 1 full stop.
Shi... vers... I forgot that at f/5.6 it IS indeed wide open at 55mm... guess I'm too used to primes...

Thanks all!
10-29-2014, 05:21 AM   #11
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QuoteOriginally posted by LensBeginner Quote
In my experience a 50mm on the K-01 will be noticeably softer at f/8 than at f/5.6 due to diffraction, on a test chart at least...
As for thin DoF, I think focus was ok, and would not blame it for softness.
Eh...f/8 is a pretty good place to be on APS-C cameras. Diffraction will start to become a factor around f/11 and be noticeable at f/16.
10-29-2014, 06:13 AM   #12
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QuoteOriginally posted by vonBaloney Quote
Eh...f/8 is a pretty good place to be on APS-C cameras. Diffraction will start to become a factor around f/11 and be noticeable at f/16.
It really depends on pixel pitch... on my K100D Super, well, maybe even f/11 was the hot spot, on a K-01, I believe f/5.6 is best, at least at that focal length...

Pixel pitch for the former is ( 24mm * 1000 ) / 3'008 = 7.98μm, for the latter ( 24mm * 1000 ) / 4'928 = 4.87μm (figures rounded to the nearest decimal)
Diameter of Airy disk is 7.5, 10.7, 14.7 and 21.3μm at f/5.6, f/8, f/11 and f/16 respectively.
Thus, when viewed at 100% magnification of course, the K100D is diffraction limited only at f/16 (7.98μm * 2 = 15.96μm < 21.3μm), while the K-01 is diffraction limited at f/8 (4.87μm * 2 = 9.74μm < 10.7μm)

I also agree that shooting wide open is more a limitation to image quality than it is being right there on the brink of diffraction... however I wouldn't be shooting much at f/8 on a K3 if I were to seek the absolute maximum picture quality and sharpness for a particular purpose (disregarding for the sake of the argument all other artistic and technical limitations)...

Of course the K-01 at f/8 will still resolve more than the K100D at f/11... but that's not because of diffraction!!!
10-29-2014, 07:56 AM   #13
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QuoteOriginally posted by LensBeginner Quote
It really depends on pixel pitch... on my K100D Super, well, maybe even f/11 was the hot spot, on a K-01, I believe f/5.6 is best, at least at that focal length...

Pixel pitch for the former is ( 24mm * 1000 ) / 3'008 = 7.98μm, for the latter ( 24mm * 1000 ) / 4'928 = 4.87μm (figures rounded to the nearest decimal)
Diameter of Airy disk is 7.5, 10.7, 14.7 and 21.3μm at f/5.6, f/8, f/11 and f/16 respectively.
Thus, when viewed at 100% magnification of course, the K100D is diffraction limited only at f/16 (7.98μm * 2 = 15.96μm < 21.3μm), while the K-01 is diffraction limited at f/8 (4.87μm * 2 = 9.74μm < 10.7μm)

I also agree that shooting wide open is more a limitation to image quality than it is being right there on the brink of diffraction... however I wouldn't be shooting much at f/8 on a K3 if I were to seek the absolute maximum picture quality and sharpness for a particular purpose (disregarding for the sake of the argument all other artistic and technical limitations)...

Of course the K-01 at f/8 will still resolve more than the K100D at f/11... but that's not because of diffraction!!!
Diffraction is generally more lens-dependent than sensor-dependent. For example, on FF, the Canon 85/1.2 is already showing (marginal) effects of diffraction at f/5.6. With most lenses, once you are more than 2 stops down, center sharpness begins a slow decline. Of course, once you are stopped waaay down, you get the worst of both worlds.

WRT "absolute maximum picture quality and sharpness" at f/8 on the K-3, well, that depends. f/8 on many lenses leads to a slight decline in center sharpness but an increase in edge sharpness due to the increased DoF compensating for field curvature.
10-29-2014, 08:01 AM   #14
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My personal non scientific experience is that fast lenses have their sharpest rendering at 5.6 and kit lenses performed better at f9.
10-29-2014, 08:21 AM   #15
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Two stops from wide-open is a good rule of thumb, but it is only a rule of thumb -- depends on the lens...
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