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03-28-2016, 02:59 PM - 1 Like   #1
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Is this what they mean by chromatic aberration?

Hi All,

Not sure if I got the right term or if it's CA, but when I got my K-3 I shot pix of the moon with a used lens and noticed the green and red outlines on the moon. Oh well, I figured that it was just an older lens. However, when I used my new 18-135, I noticed the same thing when I zoomed in; coloured outlines (red and green) on objects. It's very noticeable around the first smoke stack, the red brick one.

I'm using Corel AfterShot Pro2 as my RAW viewing software.

So:
  • Am I just guilty of pixel peeping and can stop rocking myself to sleep at night in the fetal position?
  • Is this the standard output from the K-3?
  • Do I need to tweak some initial settings?
Any insight appreciated.


A jpg of the RAW photo is attached.


Take care,
Newfie

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03-28-2016, 03:13 PM - 1 Like   #2
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Hey there, hows it going?
QuoteOriginally posted by Newfie Quote
However, when I used my new 18-135, I noticed the same thing when I zoomed in; coloured outlines (red and green) on objects. It's very noticeable around the first smoke stack, the red brick one.
Seems like you are describing lateral CA. If you shoot jpeg, there is an in-camera correction tool available. If you shoot raw, many software allows automatic lens profiles, and some others allow just manual CA corrections.
Pretty much any lens will have some degree of CA (axial/longitudinal or the lateral: lateral is more easy to fix), though some more than others. Usually it is most noticeable at wide open apertures in the edges of the frame with high-contrast subjects. You can look at lab tests of lenses, as many reviewers check CA on the lens and give it some sort of rating. Note that there are other optical faults beside CA, which have different causes.

QuoteOriginally posted by Newfie Quote
Am I just guilty of pixel peeping and can stop rocking myself to sleep at night in the fetal position?
Yes. But also no. I mean, we all do it. One you notice it, you cannot unsee it. But keep in mind that most audiences will not really notice it, unless it is really destroying the image. CA rarely makes or ruins a photo. But I know that it can annoy photographers. Thankfully, lens profiles are a thing. While I don't like distortion and vignetting corrections, CA correction is quite good.
QuoteOriginally posted by Newfie Quote
Is this the standard output from the K-3?
CA is a lens problem, not camera problem. But a camera with a much smaller MP count will have fewer pixels capturing the CA, so it might appear less noticeable. So yes, a modern camera with high MP will capture everything beautifully, even optical faults. New cameras are simply more demanding on lenses than older sensors /film

QuoteOriginally posted by Newfie Quote
I'm using Corel AfterShot Pro2 as my RAW viewing software.
So check lens profiles for that lens. You can try manual adjustments as well, or make your own profile. There should be a tab with a database where you can choose brand, or possibly it will be found for you automatically.
03-28-2016, 03:15 PM   #3
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Looks like purple and green fringing to me, yes, a form of CA. Something to do with lightwaves and colour frequencies not matching up .....(as you can tell the technical side of it is beyond me!). Can be tricky to remove as simple colour channel de-saturation (eg magenta) doesn't always work. But there are specialised tools within software like LR that might help.
03-28-2016, 03:36 PM - 1 Like   #4
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Good tech (but clear) explanation

Chromatic aberrations

03-28-2016, 03:40 PM   #5
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The 18-135 is particularly prone to this sort of CA, especially near the edges. But it's gone with one click of a button in LR. I'm sure the Corel software will have something similar, perhaps involving manual correction with a slider. It really is a non-issue these days.
03-28-2016, 04:19 PM   #6
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Thanks Gang,

Yep found a way to manually get rid of it in Corel AfterShot Pro 2. However, the program doesn't have the K-3 or it's lenses in the database. I'm off to the Corel forum to see if other Pentaxians have developed custom settings or good work flows.

Take care,
Newfie
03-28-2016, 04:23 PM   #7
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For a shot like that with my 18-135, it's essentially a landscape... that's where I take it off and put the 60-250 on. I've seen similar effects many times on the 18-135 wide open at 135mm.
03-28-2016, 05:26 PM   #8
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QuoteOriginally posted by mcgregni Quote
Looks like purple and green fringing to me, yes, a form of CA. Something to do with lightwaves and colour frequencies not matching up .....(as you can tell the technical side of it is beyond me!). Can be tricky to remove as simple colour channel de-saturation (eg magenta) doesn't always work. But there are specialised tools within software like LR that might help.
Greetings, my understanding of purple fringing is when a shot is taken where there is too much contrast. I would get this a lot when shooting with my Nikon N8008s film SLR using a AF Nikkor 70~210mm non D Lens. I went back into the instruction manual and discovered that a program i, e, Pd, Program Dual compensated for when the lens was set beyond 135mm. So, essentially it becomes a different lens. That did the trick for me as I never again ignored the commands.
Thanks for your comment, always fun to learn something new.

Rgds,

Tonytee

03-28-2016, 05:27 PM   #9
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I typically use the in-camera correction for CA with the 18-135 whenever I use it. Works well.
03-28-2016, 07:10 PM   #10
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QuoteOriginally posted by Newfie Quote
Hi All,

Not sure if I got the right term or if it's CA, but when I got my K-3 I shot pix of the moon with a used lens and noticed the green and red outlines on the moon. Oh well, I figured that it was just an older lens. However, when I used my new 18-135, I noticed the same thing when I zoomed in; coloured outlines (red and green) on objects. It's very noticeable around the first smoke stack, the red brick one.

I'm using Corel AfterShot Pro2 as my RAW viewing software.

So:
  • Am I just guilty of pixel peeping and can stop rocking myself to sleep at night in the fetal position?
  • Is this the standard output from the K-3?
  • Do I need to tweak some initial settings?
Any insight appreciated.


A jpg of the RAW photo is attached.


Take care,
Newfie
What you have there is purple fringing and sometimes it could appear to be different colors. The fringing is a result of the lens being not quite apochromatic. As not all wavelengths are focused in the same plane, you get colored ghosts at borders with great contrast. There are few fully APO lenses made, and even fewer are zooms... Good post processing software can automatically detect the fringing and correct it. Hope this helps.

Tony
03-29-2016, 03:18 AM - 1 Like   #11
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You might have to update your software to the latest version to get updates for new cameras and lens profiles. And there might be a way to make your own. Good luck!

(and I don't agree with purple fringing comments; to me purple fringing is the purple colour on high contrast edges; it is different from axial or lateral CA because those are a measurable shift in colour spectrum, and can be aligned. Purple fringing doesn't happen on just one direction, but it happens around any high contrast edges. Its not a shift, its a "glow")
04-05-2016, 11:24 AM   #12
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QuoteOriginally posted by Paul the Sunman Quote
The 18-135 is particularly prone to this sort of CA, especially near the edges. But it's gone with one click of a button in LR. I'm sure the Corel software will have something similar, perhaps involving manual correction with a slider. It really is a non-issue these days.


About six clicks--the "remove CA" checkbox was a good start, but there was still some pesky fringing in those branches.

This adjustment took about two minutes from import to export. It's fantastically easy to manage in Lr, not sure about the OP's Corel software.

But yes, relax--this is one of the easiest lens distortions to fix in post.
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