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09-26-2010, 05:41 PM   #1
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DA70mm purple fringe... why?

Hey all,

(I hope this is the right area to post this, as it is about one lens.)

So, I downloaded the photos I took today and was flipping through them when I noticed some very prominent purple fringe on a number of photos that I took with my DA70 at f2.4 (using my K-7).

I normally shoot RAW, but todays photos were all shot JPG as I forgot to switch back after playing around the day before.

What would have caused this to happen to badly? Was the chrome just too bright? (I can't tell how blown it was as it was shot JPG.) I wouldn't expect it to happen with this lens, especially not so close to the center.

(You can also see a tiny bit of red/blue fringe in the rear wheel and brake disc, that's more like what I would expect.)

Here's the full image (shrunk) and 100% crops from a few areas.

Any ideas? How can I prevent this? (Apart from not taking anymore photos )









09-26-2010, 05:53 PM   #2
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This behavior is quite common, and will happen with any lens due to the refraction that occurs when strong light bounces off of of highly-reflective surfaces. That's just plain optics for you

It can be a lot worse with other lenses, and judging by how the regular version of this photo looks, I'd say you should be quite pleased with the results!

Adam
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09-26-2010, 06:35 PM   #3
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I agree with Adam, that amount of fringing given the subject, especially wide open, is a good result.
09-26-2010, 07:17 PM   #4
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I agree with the others - this amount of PF is nothing to worry about.

I'll also add that with some lenses, the PF is also a function of the focus point - with these lenses, high-contrast edges that are back-focused will exhibit more PF. I don't know if the DA70 falls into this category, but if the PF really bothers you you could try experimenting with changing the focus to see if it helps to reduce the amount of PF.

09-26-2010, 09:45 PM   #5
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As others have said, this is mainly an issue wide open with very high contrast edges. So don't shoot those kind of edges wide open if this pretty small amount of fringing is a problem for some reason (like maybe in a print 11x14" or larger).
09-26-2010, 10:15 PM   #6
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QuoteQuote:
Gregx999: Any ideas? How can I prevent this?
Yes, you can use smaller apertures--that would allow you to make large prints without a problem. As everyone has said; there is nothing out of the norm in this shot.
09-27-2010, 06:10 AM   #7
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Ok, I just need to more careful with chrome I guess.

Here's a similar shot taken with my DA15. I didn't include any 1:1 zooms, but you can definitely see less purple fringing in this shot. Zoomed in, it's there, but maybe only 10-20% of what's there in the shot with the DA70. (True, the bike is larger in this shot than the other, but it still seems the DA15 was controlling the fringe a bit better.)

09-27-2010, 09:08 AM   #8
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What I see in the second picture are less pronounced shadows, which means less direct light, which would reduce purple fringing on any lens. Those two lenses are rather good when it comes to purple fringing; you would see considerably more with your kit lens at a wide-angle setting.

As Adam and Marc have said, this is a problem with optics--one of the many things in photography where the image captured differs from the scene as our eyes see it. I would recommend spending some time trying to create purple fringing in your shots, so as to better understand what causes it, and then find ways to reduce or avoid it. (Look for high contrast scenes, like trees backlit by a bright sky or chrome next to black leather.) That will serve your future photography better than just a warning flag popping up every time you see chrome.

Hope this helps.

04-20-2011, 09:51 AM   #9
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Fringe with Mirrored Lenses?

Is there a distinction in the amount of fringe between glass and mirror lenses?

Thanks very much!
daviddstubbs

Last edited by daviddstubbs; 04-21-2011 at 10:45 AM.
04-20-2011, 09:59 AM   #10
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The K-5 has a CA module built-in for lenses. Have you tried using this to see if would help?
Aside from this it looks as though there is some lateral CA in the scene also(atop the PF), which I think would likely be addressed using lens profiles with apps such as(LightRoom, Adobe Camera Raw etc).

And finally, for the most part PF is very easy to deal with.
I'm not saying its not an issue, because edge contrast PF will often be associated with edge blooming. However, it is very easy to fix either with software such as Helicon Focus and many of the editing software available today.

Still, it is never fun to have to deal with this after the fact.
And there's no doubt that some lenses are far more apt to controlling such things in such conditions. But... for the common shooter, we are left with software control measures due to the costs of better glass.
04-20-2011, 10:55 AM   #11
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As others have said, it's nothing out of the ordinary.

Moreover, the first shot looks great when viewed at web resolution, and the fringing isn't at all apparent. Nice shot!
04-20-2011, 02:15 PM   #12
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QuoteOriginally posted by GregX999 Quote
Ok, I just need to more careful with chrome I guess.

Here's a similar shot taken with my DA15. I didn't include any 1:1 zooms, but you can definitely see less purple fringing in this shot. Zoomed in, it's there, but maybe only 10-20% of what's there in the shot with the DA70. (True, the bike is larger in this shot than the other, but it still seems the DA15 was controlling the fringe a bit better.)
The DA70 shot is at f2.4. You don't say what the DA15 aperture was, but even wide open it is f4.0. PF is mitigated at smaller aperture settings.
04-20-2011, 02:20 PM   #13
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QuoteOriginally posted by daviddstubbs Quote
Is there a distinction in the amount of fringe (not chromatic aberration) between glass and mirror lenses?

Thanks very much!
daviddstubbs
PF can occur with any lens anywhere there is a high degree of contrast. For instance, it is quite common to see PF on tree branches against a sky, especially if the sky is overcast or blown out. PF can be reduced by stopping down the lens. It can also be removed in post-processing.
04-20-2011, 03:08 PM   #14
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This must be a bad week for the da 70 first my harsh bokeh shot and now this evidence of purple fringing.
04-20-2011, 04:38 PM   #15
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QuoteOriginally posted by selar Quote
This must be a bad week for the da 70 first my harsh bokeh shot and now this evidence of purple fringing.

Sent from my GT-P1000T using Tapatalk
Not a bad week for the DA70 at all. Any lens can exhibit harsh bokeh and/or PF under certain conditions and in certain situations. It is the photographer's job to get the best out of his equipment.
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