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06-27-2009, 07:35 AM   #1
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DA 18-55 AL II advices

I just bought my first pentax a K20D and it came with the common kit lens 18-55.
I thought it was the best for me to start with this kit lens and see how it performed, then later if I liked the system (Pentax) buy better lenses.
Sorry in advance if this was already asked.
I wold apreciate if anyone has som tips for this lens like what are the best f stops for each focal lenght.
From my short tests I found out this lens is very soft at the corners in max aperture, in every focal lenght. To tell you the truth I was a bit dispointed with the results I got.
Thanks for any feedback.

06-27-2009, 09:23 AM   #2
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f/8 is pretty much the best aperture all around. At f/8 or f/11, it's actually about as good as most primes.

Not sure what you're comparing it to, but it's actually also better than most other kit zooms even wide open - although clearly, nowhere near as good as a decent prime or a more expensive zoom.
06-27-2009, 01:27 PM   #3
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I'm not comparing it to other lenses, I just took the pictures and saw the results.
Here is one of the photos that get me intrigued, it was taken at 18mm- f8, so I expected it to be reasonably sharp all over and that's not the case. Attention heavy image.
http://www.majhost.com/gallery/rupi/stuff/imgp0316.jpg
Its the original 10Mp jpeg image, no postprocessing at all (except the one that the camera does).
I don't understand why the sides are so blurred (especialy the left).
Please, do not comment on the compositon, bad light, etc, forget it, I know it's not a good photo is just to ilustrate my question.
Thank you for any feedback.
06-27-2009, 01:33 PM   #4
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Focus seems ok... No apparent motion blur... I think you lens is defective. Definitely. It shouldn't be like that, not even wide open. I had that lens too.

06-27-2009, 01:53 PM   #5
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QuoteOriginally posted by kristoffon Quote
Focus seems ok... No apparent motion blur... I think you lens is defective. Definitely. It shouldn't be like that, not even wide open. I had that lens too.
I'm sure It's not motion blur, speed was 1/500. well i have to test this lens in a more methodic way. If it's defective lens I still have the 15 days period to return it. It's better to solve this as soon as possible.
Please check this other image, same conditions, same blurred edges (again on the left).
http://www.majhost.com/gallery/rupi/stuff/imgp0312.jpg
06-27-2009, 02:20 PM   #6
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Here is an example shooting with 18mm @f16 with the kit lens, to my eye it is very sharp and not a bad lens at all.

06-28-2009, 09:26 AM   #7
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QuoteOriginally posted by rupi Quote
I'm not comparing it to other lenses, I just took the pictures and saw the results.
Right, but what was setting your expectations? I'm guessing you are used to the nearly infinite DOF of P&S cameras. The sample picture you posted appear sharp enough at the distance focus appeared to be - maybe 10 meters away? I think you're expecting f/8 to yield infinite and perfect DOF even when viewed at 100%, and that's just not realistic. The sides are not at the same distance as the focus point; they won't be in perfect focus. The people in particular are considerably closer. If you want to test the lens sharpness at the edges, you want a scene in which you know for sure there is something in focus at the edges. For example, something on an angle, not straight on.
06-28-2009, 11:08 AM   #8
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QuoteOriginally posted by rupi Quote
I'm sure It's not motion blur, speed was 1/500. well i have to test this lens in a more methodic way. If it's defective lens I still have the 15 days period to return it. It's better to solve this as soon as possible.
Please check this other image, same conditions, same blurred edges (again on the left).
http://www.majhost.com/gallery/rupi/stuff/imgp0312.jpg
The top of the tower would be about the same distance as the round ornament on the middle... I still say defective, but to remove all doubt you should shoot a flat wall from a 90 degree angle as Marc said.

06-28-2009, 01:58 PM   #9
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QuoteOriginally posted by kristoffon Quote
The top of the tower would be about the same distance as the round ornament on the middle... I still say defective, but to remove all doubt you should shoot a flat wall from a 90 degree angle as Marc said.
Thank's
I'll do that as soon as possible. I really want to take any doubts about the lens quality.
06-28-2009, 02:54 PM   #10
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The kit lens I & II are both very good lenses in day time usage, very sharp pretty much at all aperture. I use my in camping or hiking, result are great. and AL II is a little smaller, but overall both are the same.
07-08-2009, 08:45 AM   #11
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Did the "brick wall test" with the 18-55 ALII lens and I think it is OK.
I guess I was expecting to high from this lens. It is decent, but not great.
If I want some sharpness at 18mm I have to shoot at f8.
But I really need to start collecting money for a better and more specific UWA lens
If someone wants to chek my test pictures (caution 10Mp images).
Thank's for the feedback.
07-08-2009, 09:04 AM   #12
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QuoteOriginally posted by rupi Quote
I'm not comparing it to other lenses, I just took the pictures and saw the results.
Here is one of the photos that get me intrigued, it was taken at 18mm- f8, so I expected it to be reasonably sharp all over and that's not the case. Attention heavy image.
http://www.majhost.com/gallery/rupi/stuff/imgp0316.jpg
Its the original 10Mp jpeg image, no postprocessing at all (except the one that the camera does).
I don't understand why the sides are so blurred (especialy the left).
Please, do not comment on the compositon, bad light, etc, forget it, I know it's not a good photo is just to ilustrate my question.
Thank you for any feedback.
The left side in this photo has more contrast in the subject, while the right side is shaded. I see more Chromatic Aberration in those contrasty areas, which makes the left side look softer to me. If you have software to remove CA, it might look better.
07-08-2009, 09:11 AM   #13
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QuoteOriginally posted by rupi Quote
Did the "brick wall test" with the 18-55 ALII lens and I think it is OK.
I guess I was expecting to high from this lens. It is decent, but not great.
If I want some sharpness at 18mm I have to shoot at f8.
Part of that is the lens getting sharper as you stop down, but part of it is also that the focus "plane" with most lenses is not completely flat. If you focus on a given spot one wall right in front of you, a lens really wants everything *at the same distance* to be in focus. But the sides of the wall are not at the same distance - they are farther away from you. The wall would have to curve toward you on both sides in order for the sides to be the same distance from you as the center.

Now, most lenses attempt to correct for this in their designs to *some* extent, but aside from macro lenses, most still focus on a curve. So the soft corners you see at wide apertures are at least partially the result of them being further away from you, and hence outside the focus zone. As you stop down DOF gets big enough that the corners becomes in focus.

Which is to say, virtually *all* lenses will do this to some degree; it's not a sign of a bad lens, but rather, of a bad test. Shoot a walls that is curved in the way the lens expects and the corners will look better even wide open. But of course, not perfect - lenses *are* usually sharper in the center.
07-09-2009, 10:12 AM   #14
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I think the kit lens is quite good, maybe give it a second shot (after being repaired, if needed) before dismissing it. I keep thinking to myself that I have to upgrade this lens, because it is afterall just a lowly kit lens. But I look at the photos I get, and I'm not dissappointed.

To further justify to myself that I shouldn't upgrade, I look at this lens review where the acclaimed FA31 ltd is compared to, of all things, the kit lens.

Pentax FA 31mm f/1.8 AL Limited observations robertsdonovan.com

Scroll down to the comparisons of the FA31 and 18-55 II at the F4, the kit lens looks VERY good to my eyes when compared to the FA31. The kit lens, IMO, is great as an outdoor lens. I've yet to find a comparison to the kit lens (for example, the DA 16-45) that would make me think to myself that I HAVE to upgrade it when it's compared in similar focal lengths and apertures....and yes I've been searching for one!

I'm thinking that investing in a versatile prime that would give me more low light (fa31), or macro capabilities (da35 macro) would give me more bang for my buck....everyone's different in that regard though.
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