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09-16-2014, 04:28 PM   #1
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40mm XS bluriness/softness problem

So I'm having trouble with my Pentax 40mm XS pancake lens, it was a great lens very handy for street photography and for anything where I needed to travel light but one day while out in a bit of rain, (Damn Irish weather) it got a bit wet and it's never been right since. It still autofocuses ok but the lens seems a lot softer than before (it was never a super sharp lens) the corners are very soft even at f9, I looked through the lens with a torch and it seems fine, no condensation/fungus, so what could it be? (Pentax K5), any help appreciated
Full Res sample images here https://www.dropbox.com/sh/fjfsqc9fhxsq8kr/AADOnnCLmj8jrKOnh0oWtVQma?dl=0

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09-16-2014, 04:41 PM   #2
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The only issue that really stands out in my eyes is the ISO noise in the shadows ... because you shot this at ISO 400. I really would have used ISO 100 or 80 for this shot ... particularly since your shutter speed was so high at ISO 400.

You would arguably get better sharpness as well if you had stopped down to f/8 or f/11 or maybe even f/16. Diffraction "might" become an issue with some of the fine details at f/11 and f/16 but the added DOF would improve the visual perception of overall sharpness.

Other than that, I don't know how much more we can expect from a lens that retails for $250 or less (US).
09-16-2014, 05:11 PM   #3
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Have you tried autofocus adjustment on the K-5 menus? I have both the 40mm limited and XS version and both are pretty sharp wide open.....
09-16-2014, 05:53 PM   #4
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QuoteOriginally posted by effet.de.nuit Quote
So I'm having trouble with my Pentax 40mm XS pancake lens, it was a great lens very handy for street photography and for anything where I needed to travel light but one day while out in a bit of rain, (Damn Irish weather) it got a bit wet and it's never been right since. It still autofocuses ok but the lens seems a lot softer than before (it was never a super sharp lens) the corners are very soft even at f9, I looked through the lens with a torch and it seems fine, no condensation/fungus, so what could it be? (Pentax K5), any help appreciated
Full Res sample images here https://www.dropbox.com/sh/fjfsqc9fhxsq8kr/AADOnnCLmj8jrKOnh0oWtVQma?dl=0
Can you post a photo or 2 that were not taken at infinity focus?

09-16-2014, 07:19 PM   #5
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Have you tried manually focusing it to see if the auto focus is wrong? I used to own this lens and it was tack sharp at basically all f stops.
09-16-2014, 07:55 PM   #6
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Take some shots focussing with live view. That should eliminate focus error as a possible cause.
09-17-2014, 03:44 AM   #7
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Hello everyone and thanks for the answers but the image above was one of the clearer ones here is a recent pic to show the softness, (the others didn't upload it seems), I will try to take some that are not focused at infinity

---------- Post added 09-17-14 at 12:48 PM ----------

QuoteOriginally posted by JJJPhoto Quote
The only issue that really stands out in my eyes is the ISO noise in the shadows ... because you shot this at ISO 400. I really would have used ISO 100 or 80 for this shot ... particularly since your shutter speed was so high at ISO 400.

You would arguably get better sharpness as well if you had stopped down to f/8 or f/11 or maybe even f/16. Diffraction "might" become an issue with some of the fine details at f/11 and f/16 but the added DOF would improve the visual perception of overall sharpness.

Other than that, I don't know how much more we can expect from a lens that retails for $250 or less (US).
Hi JJJphoto, and ye that was a bit noisy but that was shot before the incident, I uploaded a recent photo to show the bluriness at f9, almost usable in the center but very soft on the outside, I don't usually shoot much over f8/f9 so diffraction shouldn't be much of an issue
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09-17-2014, 03:48 AM   #8
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Try cleaning/wiping the lens front and back element (maybe invest in a lens cleaning kit? its handy for all lenses). Make sure it is stopping down to the aperture you selected.
And yes, I think this lens is optimized for closer focus than infinity. Like, under 30m. The sample photos you posted so far are not terrible. Hot, hazy days tend to blur some detail, and since this is 40mm, your DoF is not nearly as thick as that of an ultra wide. The other "problem" for the XS is that it has no lens hood, due to its small filter threads.

09-17-2014, 04:34 AM   #9
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The edges in your shot seem to be blurry, almost like something is decentered. The blurriness doesn't change based on distance. In your dropbox file, the image labeled "after" shows this most prominently. The right side of the image is blurry in a weird way.

Here are two shots I have that show it's sharpness edge to edge:
https://farm4.staticflickr.com/3919/15111822355_e0be5fbe9a_o.jpg
https://farm4.staticflickr.com/3918/15111456322_2efe922afc_o.jpg

Is the "before" picture an older picture that you thought was sharp? And the other three are shots where you noticed the blurriness?

Edit - right, from your response above, that seems to be it. Can you find a relatively flat scene (a brick wall) and shoot it at F8? That will help determine if something is decentered.
09-17-2014, 05:39 AM   #10
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Your lens is definitely faulty - I can tell you that my f2.8 shots are better than those at f8-9 you've presented. The only decent shot is that nice green landscape - looks to be fairly OK ( subject to weather condition and air clarity ) - but my copy is absolutely stunning in the centre from f2.8 - far corners are already good at f5.6 and whole frame is more or less in sharp focus at f8.
09-17-2014, 11:55 AM   #11
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@Na Horuk Thanks but I already tried cleaning the lens, back and front still no change.


@JinDesu Thanks for the sample images and I remember my lens used to be about as sharp as yours, the landscape image was from a few months ago and was sharp enough (considering it was taken while paragliding) I added a photo taken at f5 and f8 of a bookshelf to the dropbox folder and it's clearly not ok, can rain really do that much damage?

@manntax Thanks, any idea what's wrong with the lens? I thought cleaning it would solve the problem but I can't see any condensation or fungus on/in the lens and it's not exactly a big lens
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09-17-2014, 12:10 PM   #12
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Rain shouldn't cause decentering unless the water caused something inside to come loose..

Usually decentering is caused by a shock to the lens (physical impact) that shifts an element off center/tilted. I can definitely see one side being blurry in your latest two images of the bookcase.

An alternative, one that I am not familiar with so I'm only guessing, is that the rain left blurry residue on one element within the lens. That residue was only left on one side of the lens and so it makes that side blurry. I wouldn't be on this explanation as the blur in your image is very straight vertically.
09-17-2014, 12:32 PM   #13
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Yeah, I can see the edges are a little odd in these photos, and its not just DoF/bokeh.
Jin is on the right track. I think you might want to get the lens serviced or exchanged (if warranty covers this). It seems like an odd thing to be caused by rain
09-17-2014, 12:57 PM   #14
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That definitely looks bad - my lens is already sharper at f2.8 - at f5.6 it excels ! Have a look below and see what a 40mm XS lens should be like . I would either find somebody and fix the lens - or sell it for spares since the condition of photos you've shown are unacceptable indeed . (EDIT : use Right-Click context menu and click 'View Image' or 'Open Image in new Tab' or similar - just to see the full 1280px photo. Also I uploaded these from my albums - with exif intact - not sure why I cannot see the Exif option above my images, but they were shoot with K-01 off camera - scaled down for upload and not sharpened in any way )

F2.8


F5.6
04-27-2016, 01:18 PM   #15
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Hi Effet.de.nuit
Did you ever sort out the problem with your 40mm xs lens??
My own 40mm was extremely sharp and had beautiful colour rendition until a few weeks ago when somebody banged into my camera at a crowded zoo and it has been jsut like yours ever since. would love to know if you sorted the problem out.
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