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12-27-2010, 08:50 AM   #1
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Does the K5 Amplify Purple Fringing?

First off I know there is another thread on this topic, but it seems to have died without the big question being answered so I devided to make a new thred...

It is recently been brought up that the K5 may be more prone to, or amplify the effect of purple fringing in high contrast situations. For those that owned a K10, it was known to be particularly more sensitive to PF/CF than lets say the K20 or the K7, and now it sounds like the K5 may have the same quirk.

Here is a review that specifically discusses the issue.
Field Review: The Pentax K-5 (Day 3) The Phoblographer

It would be great if someone could setup a scene with high contrast (in front of a window, or bright lamp) and take some comparison shots with the K5 and K7.

If you are curious, the other thread is called "CA/CF evaluation..."

12-27-2010, 12:04 PM   #2
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Hi,
I notice purple fringes, but not with all my lenses.
Here are some exemples :
Sigma 70-300 APo, a cheap lens, i've got a lot of CA in very contrasted situations :
http://www.flickr.com/photos/lepimento/5284288136/ (i removed it with Lightroom)
Here, with a tamron 17-50 F2.8+ polarized filter, cons-day, no CA :
Untitled | Flickr - Photo Sharing!
Same lens, same situation, no CA :
Untitled | Flickr - Photo Sharing!
12-27-2010, 12:32 PM   #3
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I did notice some purple fringing, but only when shooting in very specific conditions with my DA55-300

Sky was cloudy but bright, subject was backlit from sun behind thin clouds, lens was wide open at 300mm.

Other than this situation (which I duplicated), I've not seen any major purple fringing.

Pat
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12-30-2010, 09:49 PM   #4
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I noticed in a review where the writer posted a picture that was properly exposed and another where it was underexposed (4 stops) and then pushed in post. There were two things I noticed in the underexposed/pushed image: 1) the noise was higher (as expected) and 2) purple fringing on the high-contrast tree-on-sky was much less. This makes sense when you think about it.

I haven't owned any other Pentax cameras so I can't compare, but I wonder if the PF may be a little higher because the K-5 is set to meter to the left more than previous models. It that is the case, some negative exposure comp and push in post may be helpful in problematic scenes.

12-31-2010, 03:17 AM   #5
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QuoteOriginally posted by PixleFish Quote

It would be great if someone could setup a scene with high contrast (in front of a window, or bright lamp) and take some comparison shots with the K5 and K7.

If you are curious, the other thread is called "CA/CF evaluation..."
Actually doing said test would have been the only reason to create yet another thread. I thought about doing a controlled comparison but now I lost interest.
12-31-2010, 11:02 AM - 1 Like   #6
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QuoteOriginally posted by falconeye Quote
Actually doing said test would have been the only reason to create yet another thread. I thought about doing a controlled comparison but now I lost interest.
hmmm thats helpful...

I guess I should apologize for participating in the pentax comunity and trying to help out...
01-03-2011, 10:20 AM   #7
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After reading this thread I paid attention into some of shots and surprisingly I've witnessed the same problem with some shots I've made with some of my favorite lenses. Here is an example that I've had with my DA* 50-135 F2.8 I believe The strong light from behind causes sucha thing. That has nothing to do with the quality of the body or the lens.
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01-03-2011, 10:46 PM   #8
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QuoteOriginally posted by cem.kumuk Quote
After reading this thread I paid attention into some of shots and surprisingly I've witnessed the same problem with some shots I've made with some of my favorite lenses. Here is an example that I've had with my DA* 50-135 F2.8 I believe The strong light from behind causes sucha thing. That has nothing to do with the quality of the body or the lens.
I believe it has everything to do with the lens or the body, for example my M 135 f3.5 fringes like crazy, while my K35 f3.5 never showed any fringing.

01-04-2011, 12:43 AM   #9
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if you consider more megapixels 'amplifying' then yes... otherwise no.
01-04-2011, 01:04 AM   #10
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QuoteOriginally posted by ve2vfd Quote
I did notice some purple fringing, but only when shooting in very specific conditions with my DA55-300

Sky was cloudy but bright, subject was backlit from sun behind thin clouds, lens was wide open at 300mm.

Other than this situation (which I duplicated), I've not seen any major purple fringing.

Pat
I notice PF from my K20D and the DA55-300 in exactly these same conditions, wide open @ 300mm, as well. I would imagine that a tighter crop with more pixels to work with might "amplify" the effect somewhat.
01-04-2011, 01:50 AM   #11
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QuoteOriginally posted by VaSA Quote
for example my M 135 f3.5 fringes like crazy
AOL! Funny thing is, I never noticed it on film. Is this color of a wavelength that film is quite insensitive to, or is something else going on?
01-04-2011, 05:35 AM   #12
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QuoteOriginally posted by gazonk Quote
AOL! Funny thing is, I never noticed it on film. Is this color of a wavelength that film is quite insensitive to, or is something else going on?
Well, you simply never enlarged your negatives as mush as you do with your JPG files when reviewed at 100% on your screen (without even talking about the crop factor effect that enlarge the PF even more)...

And to be honest, a 100 iso consumer neg is maybe noisier than what the K5 can produce at 800 iso, if you take the resolution into account (nothing scientific here, but based on about 200 rolls scanned on a Minolta Elite II scanner through Vuescan)...
01-04-2011, 07:37 AM   #13
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QuoteOriginally posted by dlacouture Quote
Well, you simply never enlarged your negatives as mush as you do with your JPG files when reviewed at 100% on your screen (without even talking about the crop factor effect that enlarge the PF even more)...
Not so sure about that, I have a decent slide projector and liked "wall-peep" my pictures
But of course, using the 135mm on a crop sensor enlarges the size of any PF borders.
01-04-2011, 07:53 AM   #14
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I'm not a technical person on cameras or lenses, but I have always had the same experience regarding PF.....Some lenses do it ,others don't. I never found any relationship to the body, from the DS to the K20D, it has always been a lens problem.

I had an old Quantaray 70-300 that would PF at almost any backlighting, you could count on it. It was decent otherwise, but the PF was almost always a problem.
I sold it and got the Bigma 50-500 and PF would be very hard to produce with it even if you tried. Same bodies, just a different lens.
I suspect that if you have a lens that does the PF it would be more pronounced on a16MP sensor than on a 6MP sensor....should be easy enough to test? Maybe some should go back to the DS or get some lenses that don't PF so much? Just saying.......
Best Regards!
01-04-2011, 08:34 AM   #15
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QuoteOriginally posted by gazonk Quote
Not so sure about that, I have a decent slide projector and liked "wall-peep" my pictures
Hummm, I don't know... At 100% on a conventional 1280x1024 16" monitor, a K5 image is the equivalent of a 1.30m-wide projection of an APS-C image, thus being the equivalent magnification of a 2m-wide 24x36 image, which is quite a projection.
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