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04-22-2011, 03:29 PM   #1
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HELP!!! My DA*50-135mm seems soft below f5.6

I have been shooting with my relatively new DA*50-135mm, and I noticed a consistent "softness" whenever shooting below f5.6.

I am not sure it's out of focus or motion blur, since the same scene at f5.6 looks really sharp, and I'm shooting from a far enough distance that front focus/back focus issues should not be present.

As an example, I have uploaded full size JPEGs as evidence.

The scene is daylight (slightly cloudy), shot at high speeds (min 1/750) to prevent motion blur, at apertures ranging from f2.8 to f5.6 - only the f5.6 looks sharp, the other images are slightly soft.

The sharp version (f5.6 1/750 ISO400 63mm):
f5.6 1/750 ISO400 63mm

Soft versions:
f2.8 1/3000 ISO400 58mm
f4 1/2000 ISO400 58mm
f4.5 1/1000 ISO400 63mm

Any help/suggestions will be greatly appreciated!


Last edited by Christine Tham; 04-22-2011 at 04:05 PM.
04-22-2011, 03:37 PM   #2
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I'm going to go out on a limb and say that the lens is simply that much sharper at F5.6 than below F5.6. I was never impressed with this lens's performance wide-open back when I used it, so perhaps you might be in the same boat though. It's been a while since I used the lens, however- so I could be totally wrong

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04-22-2011, 04:00 PM   #3
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You need to 3 resets all in your camera like tune up. You will be ok.
04-22-2011, 06:03 PM   #4
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Could you shoot a less busy scene at different isos to compare? It looks a little soft, particularly at f2.8, but that isn't the sort of scene that I shoot often. At the same time, I disagree with Adam, f2.8 is pretty sharp already and f4 should be quite sharp.



(shot at f4)

04-22-2011, 06:33 PM   #5
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QuoteOriginally posted by Rondec Quote
Could you shoot a less busy scene at different isos to compare? It looks a little soft, particularly at f2.8, but that isn't the sort of scene that I shoot often. At the same time, I disagree with Adam, f2.8 is pretty sharp already and f4 should be quite sharp.



(shot at f4)

I can't see your picture, but how do you get to post pictures in the Pentax Gallery? you have to be sponsored by Pentax or something? Nice shots, btw.
04-22-2011, 07:11 PM   #6
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QuoteOriginally posted by Rondec Quote
Could you shoot a less busy scene at different isos to compare? It looks a little soft, particularly at f2.8, but that isn't the sort of scene that I shoot often. At the same time, I disagree with Adam, f2.8 is pretty sharp already and f4 should be quite sharp.



(shot at f4)
Maybe my eyes have problem but your picture looks soft.
04-22-2011, 08:01 PM   #7
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Okay - I've taken a few more shots (50mm, 75mm, 135mm at f2.8, f4, f5.6 and f8 - total 12 pictures) in a consistent environment

camera on tripod, 2s delay shot - to eliminate motion blur

lens focused using Live View, and then focus locked - so no focus variation across shots

the focus is on the fur just below the bear's nose

ISO 100

Here's the link to the album containing the shots (also includes pictures from original post):
DA50-135 focus - Windows Live

My conclusion?

I think Adam is right - the lens is soft wide open - not too bad at 50mm but progressively worse at longer focal lengths

Quite sharp at f4 at 50mm

Needs f5.6 at 75mm

Really needs f8 at 135mm

Can someone else who owns the lens do a similar test and post their observations?

I'm kind of disappointed since I bought this lens for sports photography, and I don't really want to shoot at f8 all the time at 135mm to maximise sharpness.
04-22-2011, 09:24 PM   #8
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Just for giggles, I repeated the test on my primes: DA21, FA43, A50, DA70, A100, A135 - and they were all sharp even when wide open.
Pentax primes lens sharpness test - Windows Live

So much for the DA*50-135 being "as sharp as a collection of primes, but more flexible". No way, at least not wide open. At f8, *maybe*.

04-22-2011, 09:41 PM   #9
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I find my 50-135 sharp @ 2.8 < 120mm. By f4 it is razor sharp across the whole range. Sounds like something is wrong with your copy if you've ruled out af issues.
04-22-2011, 10:04 PM   #10
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QuoteOriginally posted by twitch Quote
I find my 50-135 sharp @ 2.8 < 120mm. By f4 it is razor sharp across the whole range.
Unfortunately, it's all relative.

I will agree that the DA*50-135 is sharper than other zooms I've used, it may even be the sharpest zoom out there.

I guess it's over-inflated expectations - I bought into the fanboy hype that it was "as good as a set of primes" and I'm finding out how false that comment is.

At f4 around 75mm, it's reasonably sharp (according to my test) - as long as I don't pixel peep - but being used to shooting nothing but primes for the last few years I am not really happy with the quality.
04-22-2011, 10:19 PM   #11
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QuoteOriginally posted by Adam Quote
I'm going to go out on a limb and say that the lens is simply that much sharper at F5.6 than below F5.6. I was never impressed with this lens's performance wide-open back when I used it, so perhaps you might be in the same boat though. It's been a while since I used the lens, however- so I could be totally wrong
I'm fussy, I zoom to 100% to check sharpness of all my keepers, and don't hesitate to use the 50-135 wide open <120mm. Maybe you are even fussier than me perhaps though? I'm 3,000km from my photo library so can't post examples though.
04-23-2011, 01:11 AM   #12
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Hi Christine,

I didn't take a look at your pictures, since the first link didn't gave a picture. It can be a focusproblem. So you can check ff/bf at near distance. It should be sharp using liveview, since then you don't use the AF-module in your camera. Then again it could have a different problem focussing at infinity.

I have also this lens. Just looked breafly into my bunch of pictures but I rarely use this lens wideopen. Found one at f3.2 and 135mm

So this lens can produce sharp images at wider appertures. Otherwise I would have sold it already.

Greetings Ron.
04-23-2011, 02:17 AM   #13
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Thanks Ron.

Yes, I am aware that it is possible to take nice pictures with the lens. I have taken at least a thousand shots on the lens, for example all my triathlon photos that I posted in the sports photography thread were taken on this lens, and some of them were even wide open at 135mm.

It's just that after using the lens for a little while, I have noticed a consistent softness at longer lengths wide open. It may not show up as much on some scenes compared to others, but the softness is always there when I pixel peep.

I guess my expectations were just unrealistic. The lens is not a replacement for a set of primes, and will never be. Most of my primes in the same range are sharper wide open than the DA* 50-135 is at f8.

If you rarely use this lens wide open (I don't either) then you may be like me - subconsciously compensating for less than optimal results at low f numbers. Of course, we photographers tend to worry more about DOF than sharpness, but I found myself worrying about sharpness even when I desire a shallow DOF on this lens.
04-23-2011, 02:42 AM   #14
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DA*50-135 isn't stellar lens. You can easy replace it with tamron and sigma OS equivalents. I'v found myself avoiding using it. Long time ago i'v noticed at f2.8 is less sharp and less contrasty than FA77 at f1.8!!!! the best and sharpest spot it has at 90mm. But Christine, its definetely not as bad as shows examples of yours. It is noticable less CONTRASTY AT f2.8 but there is no less details. It would be perfect lens to shoot portaits at f2.8 and postprocess it in slightly overexposed and desaturated style if you know what i mean (what i don't do).
04-23-2011, 03:02 AM   #15
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QuoteOriginally posted by Christine Tham Quote
If you rarely use this lens wide open (I don't either) then you may be like me - subconsciously compensating for less than optimal results at low f numbers. Of course, we photographers tend to worry more about DOF than sharpness, but I found myself worrying about sharpness even when I desire a shallow DOF on this lens.
It is more that I play with shallow DOF with FA*85mm and DA*55mm then I do when I go out with this lens. The AF with SDM is a bit slow to me for sports, so I don't use it for that much. It is more for having DA* and no trouble with environment (dust and rain) and mostly those pictures are more comfortable to take with f5.6 or so.
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