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12-15-2014, 07:33 PM   #1
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soft/blurry photos below f8 with SMC Pentax-DA 18-55mm F3.5-5.6 AL II

Hi everyone,

I was hoping I could get a second opinion on this. At first I thought the lens was busted because it wouldn't focus at any zoom, and i also thought it was for really silly reasons, but after I started taking test shots I'm pretty sure the issue is the lens' ability to stay sharp at higher apertures (which would conveniently match up to reports in the lens review database). I took a handful of example shots indoors and at night, so I tried to eliminate as many variables as I could.

with my K5:
-used a camera stand
-used mirror-up remote shooting
-used iso 400
-used single, center auto-focus (targeted on the hurricane glass)

The fun part is that the photos are much sharper as the aperture goes past f8 even though shutter goes up to 2". Now, I realize that this kit lens has unfavorable reviews in the lens database here for soft/blurry photos when aperture is open wide, but my results seem a bit excessive to me. This is also best case for my lens given all the controls to take these shots, practicall it seems that f10 or smaller is best. The reason I even looked into this was because I was taking casual shots outdoors in broad daylight and all of the photos were all unusable, I had initially thought it was an auto-focus issue.

Are these lenses really that bad at the wide end or is my lens worse off? (as a side, I tried using a focus calibration chart and it seemed like, when wider than f8, the lens was not sharp within the area that was focused. I did notice a little but of front-focusing but that seems like a minor problem to this).

Below the EXIF, but in order:
1) f4
2) f5.6
3) f8
4) f10
5) f13

Attached Images
View Picture EXIF
PENTAX K-5  Photo 
View Picture EXIF
PENTAX K-5  Photo 
View Picture EXIF
PENTAX K-5  Photo 
View Picture EXIF
PENTAX K-5  Photo 
View Picture EXIF
PENTAX K-5  Photo 
12-15-2014, 08:14 PM   #2
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QuoteOriginally posted by Capslock118 Quote
Hi everyone,

I was hoping I could get a second opinion on this. At first I thought the lens was busted because it wouldn't focus at any zoom, and i also thought it was for really silly reasons, but after I started taking test shots I'm pretty sure the issue is the lens' ability to stay sharp at higher apertures (which would conveniently match up to reports in the lens review database). I took a handful of example shots indoors and at night, so I tried to eliminate as many variables as I could.

with my K5:
-used a camera stand
-used mirror-up remote shooting
-used iso 400
-used single, center auto-focus (targeted on the hurricane glass)

The fun part is that the photos are much sharper as the aperture goes past f8 even though shutter goes up to 2". Now, I realize that this kit lens has unfavorable reviews in the lens database here for soft/blurry photos when aperture is open wide, but my results seem a bit excessive to me. This is also best case for my lens given all the controls to take these shots, practicall it seems that f10 or smaller is best. The reason I even looked into this was because I was taking casual shots outdoors in broad daylight and all of the photos were all unusable, I had initially thought it was an auto-focus issue.

Are these lenses really that bad at the wide end or is my lens worse off? (as a side, I tried using a focus calibration chart and it seemed like, when wider than f8, the lens was not sharp within the area that was focused. I did notice a little but of front-focusing but that seems like a minor problem to this).

Below the EXIF, but in order:
1) f4
2) f5.6
3) f8
4) f10
5) f13
It indeed looks out of focus on f4. F5.6 is much better. Have you tried manual focus in live view mode with 4x amplification at F4? It will remove the autofocus issue in your problem. If the issue still pesists, I suspect your lens suffers from decentering. But do not make quick conclusion.

Last edited by starjedi; 12-15-2014 at 08:20 PM.
12-15-2014, 08:33 PM   #3
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I shot that lens quit a bit when my K-x, it's just soft at f4. I used it a lot at f8 outdoor on bright days with great results.
12-15-2014, 08:41 PM   #4
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That looks excessively soft. Before blaming the lens, you might be closer than the minimum focus distance (the EXIF says Focus Range = Macro), or maybe AF failed to lock onto the lamp. If that picture is merely missed focus, the later samples with higher f-stops will look more in focus because that's a side-effect of changing aperture.

Did you redo AF between shots? If yes, maybe the first shot is the only one that misfocused. Repeat the test, autofocusing only once, then flip the camera into manual focus so the same focus is held for subsequent shots. Or maybe use manual focus starting from the 1st shot if you know how to zoom in using liveview.

Try to repeat the test moving a little further back, just in case you are too close for the lens. The 18-55 has a minimum distance of 25cm or 10 inches.

12-15-2014, 08:58 PM   #5
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I have had 3 copies of the 18-55. They perform similarly to yours. They are soft wide open, and soft before 20mm and after 50mm. They perform reasonable well at f/5.6 and up, just like your shots indicate. Mine always performed worse with a UV filter. It seemed to affect the contrast.

I actually like the lens for casual shots of people and street scenes, but it is not a razor sharp lens. It is a compromise lens at a very low price.

If you want sharp in a zoom, be prepared to spend some serious money.
12-15-2014, 09:06 PM   #6
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Looks to me there is a severe front-focus FF issue... since you have the k-5, perhaps, you could try to AF fine adjustment with -5 to -10 setting on that lens. Also, it looks like you have the focus point set to the right side.
12-15-2014, 09:20 PM   #7
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Yes, I think you should manually focus on the lamp from a reasonable distance, then go through the aperture range.


At the moment, you don't know whether it's the lens or the autofocus that's giving you grief.
12-15-2014, 10:48 PM   #8
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There is definitely something wrong - the left side is fuzzy/blurry even at f/13. Were you using center-point AF? I've owned three copies of the early first version 18-55, and have never seen softness like that, even wide-open. You need to do some testing, to see whether the problem is your AF, or the lens.

12-16-2014, 02:05 AM   #9
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Do your test in daylight first; the K5 is known for (front if I'm not mistaken) focusing issues in artificial light. I have the problem as well but haven't used it for a while in artificial light.
12-16-2014, 02:09 AM   #10
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QuoteOriginally posted by paulh Quote
There is definitely something wrong - the left side is fuzzy/blurry even at f/13. Were you using center-point AF? I've owned three copies of the early first version 18-55, and have never seen softness like that, even wide-open. You need to do some testing, to see whether the problem is your AF, or the lens.
+1

Your lens seems to be decentered in some way. I had it, used with great success on my first body K10D and it was all but soft at 18mm - softness was kicking in only at above 50mm zoom setting. Your lens has odd shaped aberrations on left side and this sort of blurring is usually associated with decentered or misaligned glass elements inside, after it's suffered severe shock.

This is actually the only lens of which I really regret selling !
12-16-2014, 04:38 AM   #11
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Try using the lens with Live View!
12-16-2014, 04:57 AM   #12
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If your testing on a tripod I suggest you turn shake reduction off if you haven't already done so.
12-16-2014, 04:58 AM   #13
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Wow what help, thank you all so much thus far. I'll respomd to each of you

@starjedi - yes I have tried manual focus in live view when trying a focus chart but I didn't have confidence in it. The camera seemed to perform differently in live view. I'll try this again after a few suggested it.

@deadjohn - I noticed it said macro too but I'm not sure why. It was mostly zoomed in (~45mm) but the base of the camera was about 2'-3' away from the focus target.

@hamiltom - my experience is almost consistent with yours except the soft focus for my lens seems to be at any focal length, not just at the extremes. These shots for instance were around ~45mm.

@aleonx3 - I tried fine adjustment when I used a focus chart but only when I was using f5.6, I'll try that again under another aperture.


@clackers / @paulh - center focused but I'll note that I'm pretty sure ff or bf is happenening because after the camera focuses I can still improve the focus by a bit, always a counter clockwise adjustment by a hair.

@sterretje - I'll test daylight today. This issue came up because of focusing problems in the daylight.

So curious question: what does live view benefit from that view finder does not? I've been blaming the lens so far because my 50-200 doesn't seem to have a problem, but since I definately cannot use that lens indoors my perception might have some bias. Informal outdoor testing seemed sharp though I'll get some outdoor shots today.
12-16-2014, 05:05 AM   #14
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Live view uses an alternative method to determine focus in AF over the viewfinder. It's slower so its not used much for many aspects of dSLR work but it typically is more accurate. The K-01 only has that method. Its useful on tripod and when speed of capture is not essential.
https://www.pentaxforums.com/forums/6-pentax-dslr-discussion/202226-normal-cd...than-pdaf.html
http://lxcellent.blogspot.com/2012/12/understanding-cdaf-and-pdaf.html
12-16-2014, 06:20 AM   #15
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You don't have a UV filter on the lens? If you do take it off and see if things improve.
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