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02-27-2011, 06:37 PM   #1
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Purple fringing - is it more prevalent on the K5?

I've noticed quite a few of my photos have a purple fringe around bright lights - here is an example:


The fringing seems more prevalent at high ISO.

I've also noticed purple fringing on my K10D, but not at this level. Of course, I generally don't go above ISO800 on the K10D, whereas on the K-5 I've been shooting at lot of photos at ISO3200.

Any comments?

02-27-2011, 06:43 PM   #2
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There have been a few threads on this topics, here's one of them.

I can say from personal observations that there does seem to be more PF with the K-5 than with my previous bodies.
02-27-2011, 06:51 PM   #3
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Between sensor spots, AF issues and PF the K-5 is taking a beating. It has the potential to be such a great camera. The PF does seem to be an issue for some people, but others seem to be just fine. Sounds like a QC problem.
02-27-2011, 07:01 PM   #4
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Thanks - interesting read!

I also found this blog article that seems to suggest that purple fringing can be camera specific:
OK1000 Pentax Blog: Reducing Purple Fringing and Sensor Blooms

Sounds like there's not much I can do about it.

I'm reasonably certain my K10D does not produce artefacts that are as pronounced - I will try and take some test shots comparing the two cameras on the same scene and same lens.

02-27-2011, 07:08 PM   #5
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QuoteOriginally posted by Winder Quote
Between sensor spots, AF issues and PF the K-5 is taking a beating. It has the potential to be such a great camera. The PF does seem to be an issue for some people, but others seem to be just fine. Sounds like a QC problem.
The sensor stains are what they and the issue is hopefully resolved (I had to return two K-5 bodies due to stains). The AF issue is still up in the air, but it sounds like a problem that's less about QC and more about a design/software issue (maybe). As for the PF, I don't think that's a QC issue, nor do I think different bodies have different levels of it. I've now owned 3 bodies and can't say there was any difference between them in terms of PF. However, there is variation from lens to lens and shot to shot, so the fact that some people are having more issues with it is likely due to what they're shooting and the lens they're shooting it with as opposed to a QC issue.
02-27-2011, 07:25 PM   #6
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Okay - here are some test shots - all are taken on the A135mm/2.8 lens - manual focus

K10D:


K-5 EV +1:


K-5 EV -1:


K-5 EV 0:


I think the issue here is that the K-5 appears to be over-exposing by about 1 EV compared to the K10D. The K-5 EV-1 photo appears roughly the same as K10D in terms of purple fringing.

The K10D has a KatzEye focusing screen.

The K-5 has a focusingscreen.com focusing screen.

I suspect the focusingscreen.com focusing screen is causing a K-5 exposure error.

Based on this, I think I might have to ditch the focusingscreen.com screen and buy a KatzEye.
02-27-2011, 07:56 PM   #7
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I have a theory that as resolution increases, we are going to see more and more of this sort of thing. I do wonder if it is a side issue with weak AA filters, which Pentax has chosen to use as a way of getting as much resolution out of their cameras as possible.
I have a friend who uses a Canon 7D, and I know he is fighting with PF all the time.
02-27-2011, 07:58 PM   #8
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I guess you found some answer to your question


BTW, check focusing as well. When I got my FA135/2.8 on K5, I had thought it was very prone to PF as well. Turns out that it needed focus compensation and the PF was totally gone.

02-27-2011, 08:05 PM   #9
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I found both my K10D and K20D underexpose compared to my K-5. I have not noticed any purple fringing on my K-5
02-27-2011, 08:12 PM   #10
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I think I've pretty much decided there's not much difference between the two cameras based on my test shots (once the exposure difference is compensated for), but the real issue is comparing the viewfinders, the focusingscreen.com screen is well ... terrible ... compared to KatzEye.

I was hoping to save money by buying focusingscreen.com - guess I should just have ponied up the cash to buy KatzEye in the first place.

Oh well - lesson learnt. Will go ahead and order a KatzEye now (seriously considering going for OptiBrite this time)
02-27-2011, 08:46 PM   #11
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Do you have a Katzeye on hand to compare against the focusing.com screen? You sound like you do not have the Katzeye yet?
02-27-2011, 08:51 PM   #12
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What lens was used in your first photo?
With regards to your other photos, as someone who also owned the A 135mm f/2.8, it is not that terrific in terms of optical performance with its 4 element design. I think the superior image resolution of the K-5 just shows up the shortcomings of certain lenses all the more obvious.
02-27-2011, 09:17 PM   #13
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QuoteOriginally posted by gtl Quote
Do you have a Katzeye on hand to compare against the focusing.com screen? You sound like you do not have the Katzeye yet?
I don't have the new KatzEye Plus - i was comparing the focusingscree.com screen on K-5 with the KatzEye on my K10D.

Anyway, I just bought the KatzEye Plus with OptiBrite, so I am looking forward to receiving it.

QuoteOriginally posted by creampuff Quote
What lens was used in your first photo?
With regards to your other photos, as someone who also owned the A 135mm f/2.8, it is not that terrific in terms of optical performance with its 4 element design.
I just checked - the first photo is DA21mm Ltd.

I agree that the A135mm/2.8 is not the world's best lens, but it has a lot of personality and character.

I find Canon lenses for example really sharp but lacking a bit in personality. The old Pentax lenses look softer and more flawed, but makes photos more interesting (just my opinion, of course). The DA Ltd lenses are sharp, but retain some of the Pentax "character" - at the end of the day I like alternating between shooting on modern lenses (with lens correction) and "old school" lenses (with no lens correction).
02-27-2011, 10:06 PM   #14
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IC. Great. You can compare the 3 different grades of screen then!
02-27-2011, 10:13 PM   #15
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QuoteOriginally posted by gtl Quote
IC. Great. You can compare the 3 different grades of screen then!
Yeah!

There wasn't a lot of difference in brightness between my old KatzEye and the focusingscreen.com screen - but the KatzEye screen area was a lot smoother - I can actually see circular marks on the focusingscreen screen which are quite distracting and muddy the view. Also the split prism goes dark really quickly. Maybe that's why it causes the K5 to over-expose (I use centre weighted metering).
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