F31fd: Is this still the magical camera? Locked

Started Feb 2, 2014 | Questions thread
This thread is locked.
photoreddi Veteran Member • Posts: 7,973
Re: Examples - DPR's own full size samples

Kim Letkeman wrote:


The point is not whether you can get CA with this camera, I can get it with pretty much any camera/lens you care to mention in certain scenarios, it's whether it's a big issue with this camera as you earlier contended, it isn't.

So you say ... but the PF is definitely a huge issue. When it strikes, it is almost impossible to remove from images without leaving obvious traces.

You should learn to use lightroom then, it's a doddle, no issues.

Lightroom handles CA fairly well (if not too strong) ...

Lightroom handles PF very poorly ... you generally have to perform nasty surgery and even then it leaves marks everywhere.

You must have a different version to me, no problems with red/green/blue/purple CA, it all works.

Purple fringing is not CA.

Everything I've seen in articles on the topic says that purple fringing is one form of CA. Lloydy even started a thread over five years ago on the topic in which you replied many times, never once claiming that "Purple fringing is not CA." Did you at some time afterwards changed your definition of PF?

Using Jpeg, I find that PFKiller works extremely well in dealing with CA (purple variety, however, CA (green variety) is a little more difficult to deal with.

Anyway, I've been playing with Raw a little and was pleasantly surprised to see that S7Raw's CA - 'Auto' function works very well. Simply using the CA - Auto button, typically, gets most of it.



One of your "CA" replies in that thread that didn't refute the PF/CA association :

So here is a clearer treatment of your example ... your blown up crops taken to 300% and recropped for clarity ... it is obvious now that the yellow side is mostly dealt with -- only a little fringing remaining, but the blue side still remains fairly strongly. In fact, I can still see CA even in your "fixed" image ...

I then applied the Shay Stephens CA remover action to the original and recropped a third time. This time it really is pretty much gone. I resized back down to a reasonable size for posting, so it is not quite as obvious again, but I think the point comes across pretty well.


And from other sources, so far I've found them to be unanimous :

The term purple fringe used to describe one aspect of chromatic aberration dates back to at least 1833. However, Brewster's description with a purple fringe on one edge and a green fringe on the other is a lateral chromatic aberration. A general defocus of the shortest wavelengths resulting in a purple fringe on all sides of a bright object is the result of an axial or longitudinal chromatic aberration. Quite often these effects are mixed in an image. Axial chromatic aberration is more subject to reduction by stopping down the lens than lateral chromatic aberration is, so the purple fringing can be very dependent on f-number: a larger f-number (smaller aperture) reduces axial aberration.



Chromatic Aberration, also known as “color fringing” or “purple fringing”, is a common optical problem that occurs when a lens is either unable to bring all wavelengths of color to the same focal plane, and/or when wavelengths of color are focused at different positions in the focal plane. Chromatic aberration is caused by lens dispersion, with different colors of light travelling at different speeds while passing through a lens. As a result, the image can look blurred or noticeable colored edges (red, green, blue, yellow, purple, magenta) can appear around objects, especially in high-contrast situations.



New Color Fringe Correction Controls

One of the new enhancements to Lightroom 4.1 RC2 is the addition of new color fringe correction controls. What exactly is a color fringe correction? This blog post is intended to explain the problem and the solution we’ve provided in Lightroom 4.1.(For ACR customers it will also be included an upcoming version of ACR7 for Photoshop CS6, currently available as a public beta)

The content in this post has been written by Eric Chan, the developer primarily responsible for implementing the solution. (Photos have been attributed where requested.)


Red-green and blue-yellow fringes at the image periphery result from lateral chromatic aberration. This problem is relatively easy to fix, and ACR & LR already have tools to do so. On the other hand, purple and green fringes in out-of-focus areas and along high-contrast boundaries are much more problematic. These fringes result from axial chromatic aberration (wavelength-dependent focus shift), aberrations in sensor microlenses, and flare. In most cases, purple fringes appear in front of the plane of focus, and green fringes appear behind the plane of focus. The aberrations can happen anywhere in the image, not just the image periphery. Sometimes, they are so strong that they’re easily spotted in small previews, such as proxies and thumbnails (thus, not only visible at 100% pixel view!). Axial CA affects nearly all lenses, from inexpensive cell phone lenses to very expensive top-of-the-line lenses. It is particularly pronounced with fast lenses at wide apertures. Hence, an improved defringe control should appeal to photographers shooting portraits, events, weddings, sports, etc. — anytime that high-speed lenses are used.


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).
Adobe’s existing “Remove Chromatic Aberration” checkbox (introduced in Camera Raw 7.0 and Lightroom 4.0), and its predecessors (Profile-based “Chromatic Aberration” slider, and manual Chromatic Aberration sliders) handles issue #1 (lateral CA) only.
The previous Defringe popup menu (Off / Highlight Edges / All Edges) in Camera Raw 7.0 and Lightroom 4.0 handles issue #4 (CCD charge leakage) only.
Up till now, Adobe did not have solutions for problems #2 (axial CA) and #3 (flare).

Notes on Axial (Longitudinal) CA

The new Defringe controls are designed to fix axial (longitudinal) CA, color aberrations due to ghosting or flare, and color aberrations (thin fringes) due to charge leakage, which affects some CCD sensors. Here’s some context on axial/longitudinal CA:

It can happen anywhere in the image (not just image borders).
It affects nearly all “fast” (wide aperture) lenses, typically most visible at the wider apertures (e.g., f/1.4 thru f/2.8).
Fringes become less visible as you stop down the lens (e.g., more visible at f/2, less visible at f/8).
Fringes are usually most visible just in front of or just behind the plane of focus.
Fringes typically appear purple/magenta when they’re in front of the plane of focus, and appear green when they’re behind the plane
of focus.
Even at the plane of focus, high-contrast edges (especially backlit) may show purple fringes due to flare.



Note: The formatting (several types of bulleted indenting) in the article greatly improves the readability, which would have taken too much time to apply to the above quote from the Adobe article.

Post (hide subjects) Posted by
MOD kwa_photo
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow