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07-12-2012, 08:38 PM   #1
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DA*60-250 Purple fringing

Just picked up my new DA*60-250, it seems to purple fringe quite a bit. Is this a bad copy or par for this lens? Clearly visible on outline of white car.

Full size jpgs here:https://skydrive.live.com/#cid=611FA57D8D41A33A&id=611FA57D8D41A33A%21536



07-13-2012, 02:46 AM   #2
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While Photozone does indicate highest CA's for that lens at 200-250mm and f4, it says they are moderate. And indeed that PF doesn't appear too bad - Lightroom would eliminate that in a second.

I am jealous that you got an actual delivery out of CRK - I've been waiting 6 weeks for my DA* 300 and there is still no firm ETA.
07-13-2012, 04:46 AM   #3
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QuoteOriginally posted by rawr Quote
While Photozone does indicate highest CA's for that lens at 200-250mm and f4, it says they are moderate. And indeed that PF doesn't appear too bad - Lightroom would eliminate that in a second.
Correct me if I'm wrong, but aren't CA and purple fringing two different things? It seems like I remember reading some reviews where Photozone said that a lens had low CA, but suffered from fringing...
07-13-2012, 05:09 AM   #4
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CA and PF are one aspect of the same thing.

Wikipedia etc have confirming descriptions of this, and DXO's write up of CA is also a good one:

"...So-called ‘purple fringing’ is essentially due to lens longitudinal chromatic aberration, causing the blue or/and red channel to be slightly defocused with respect to the green channel. When only the blue is out of focus, fringes appear blue. When both red and blue are defocused, fringes appear purple."
Chromatic aberration

07-13-2012, 05:37 AM   #5
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QuoteOriginally posted by rawr Quote
CA and PF are one aspect of the same thing.

Wikipedia etc have confirming descriptions of this, and DXO's write up of CA is also a good one:

"...So-called ‘purple fringing’ is essentially due to lens longitudinal chromatic aberration, causing the blue or/and red channel to be slightly defocused with respect to the green channel. When only the blue is out of focus, fringes appear blue. When both red and blue are defocused, fringes appear purple."
Chromatic aberration
Well, however it works, I believe that Photozone's CA measurement is not always the entire story when it comes to fringing.
07-13-2012, 11:03 AM   #6
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QuoteOriginally posted by rawr Quote
CA and PF are one aspect of the same thing.

Wikipedia etc have confirming descriptions of this, and DXO's write up of CA is also a good one:

"...So-called ‘purple fringing’ is essentially due to lens longitudinal chromatic aberration, causing the blue or/and red channel to be slightly defocused with respect to the green channel. When only the blue is out of focus, fringes appear blue. When both red and blue are defocused, fringes appear purple."
Chromatic aberration
I wouldn't take Wikipedia as the final word on this particular subject. However, even the Wiki states that not all PF can be attributed to ca.
QuoteQuote:
The term "purple fringing" is commonly used in photography, although not all purple fringing can be attributed to chromatic aberration. Similar colored fringing around highlights may also be caused by lens flare. Colored fringing around highlights or dark regions may be due to the receptors for different colors having differing dynamic range or sensitivity -- therefore preserving detail in one or two color channels, while "blowing out" or failing to register, in the other channel or channels. On digital cameras, the particular demosaicing algorithm is likely to affect the apparent degree of this problem. Another cause of this fringing is chromatic aberration in the very small microlenses used to collect more light for each CCD pixel; since these lenses are tuned to correctly focus green light, the incorrect focusing of red and blue results in purple fringing around highlights. This is a uniform problem across the frame, and is more of a problem in CCDs with a very small pixel pitch such as those used in compact cameras. Some cameras, such as the Panasonic Lumix series and newer Nikon DSLRs, feature a processing step specifically designed to remove it.
On photographs taken using a digital camera, very small highlights may frequently appear to have chromatic aberration where in fact the effect is because the highlight image is too small to stimulate all three color pixels, and so is recorded with an incorrect color. This may not occur with all types of digital camera sensor. Again, the de-mosaicing algorithm may affect the apparent degree of the problem.
Here is another discussion about ti as well.

http://www.dpreview.com/learn/?/Glossary/Optical/chromatic_aberration_01.htm

Last edited by Blue; 07-13-2012 at 11:12 AM.
07-13-2012, 11:55 AM   #7
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I dont see any CA. This looks more like PF due to sensor bloom/ charge leakage at high contrast edges.
07-13-2012, 11:57 AM   #8
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Adobe also had a good discussion on the subject with some useful examples when they introduced the improved fringing removal tools in Lightroom:

QuoteQuote:
"Color Fringing Defined
Types of Fringing
Color fringing (usually visible on high-contrast edges in the image) can result from several physical phenomena:
- Lateral (transverse) chromatic aberration (red/green fringes, blue/yellow fringes),
- Axial (longitudinal) chromatic aberration (purple and green fringes),
- Flare due to lens-lens and sensor-lens reflections (ghost images), and
- Charge leakage in CCD sensors (thin purple fringes)."
New Color Fringe Correction Controls

07-13-2012, 10:04 PM   #9
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No Purple fringing when stopped down:

12-01-2012, 02:47 PM   #10
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I'm having the same problem. Picked up my 60-250 the other day and noticed significant PF today.. will post pictures soon.
12-01-2012, 04:59 PM   #11
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Just got mine as well (funny, that -- thanks B&H), and have mainly been shooting wide open, as I am using it on the Q. So far I have not seen any significant PF, and only mild longitudinal CA.
12-02-2012, 07:32 PM   #12
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To be honest, I havent seen any PF issues with my copy after that first shot, I deleted the photo I put up in the first post, but I think it might have been a reflection off a blue car from the white car I photographed. ::face palm::
12-05-2012, 01:20 PM   #13
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QuoteOriginally posted by selar Quote
Just picked up my new DA*60-250, it seems to purple fringe quite a bit. Is this a bad copy or par for this lens? Clearly visible on outline of white car.

Full size jpgs here:https://skydrive.live.com/#cid=611FA57D8D41A33A&id=611FA57D8D41A33A%21536
For the price CA and PF should not be a constant problem ! Lets hope Pentax relaxes its price policy .
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