Chromatic aberrations terminology

[Laurentiu Cristofor]

It looks like I've been using the wrong terms to refer to some types of color fringing. But looking around, I'm still confused about what the proper terms should be.

Here is the set of fringing I am aware of and the terms I usually find it referred as:

- color fringing in high contrast areas, usually referred to as purple fringing (I'm sure I got this right). Usually purple, but I have a lens which likes to produce blue. On older lenses I see a worse version of it that I can only describe as purple blooming - it's not a simple fringe, but a blooming one . Can happen anywhere in the frame and stopping down usually minimizes it. Seems to also fall under the category of longitudinal chromatic aberrations, although that term seems to apply to more than purple fringing and it doesn't cover all reasons contributing to PF. Seems to be an issue with all focal lengths and particularly annoying in inexpensive telephotos.

- color fringing relative to the focal plane: green behind and red/purple in front. Not sure how this is called - it's referred to as bokeh fringing by photozone (I used to think incorrectly that it's called longitudinal chromatic aberrations). I see this on most fast lenses when used wide open. Most fast macro lenses also display this at apertures such as f/2.8. Fringing color is relative to focal plane and stopping down minimizes the effect. Annoying in portraits when missing focus on eyes because highlights will look either green or red.

- color fringing of purple/green variety which is more pronounced towards the edges of the frame. Fringing is also more pronounced if edges are tangential rather than radial. Seems to be called lateral chromatic aberration and I see this usually in fisheyes and wideangles, not so much in longer focal lengths.

Have I got this right? Any corrections or additions? Hopefully, we can make this thread a nice reference on this topic.

[visualopsins]

Great Laurentiu! Thanks for posting.

I would like to know what flare in highlights that causes similar color-fringing to CA is called. I say 'bloom'; there must be more technical term. Maybe flare covers it?

OF course we may begin with wikipedia infos.

[IAZA]

I definetly will always watch this thread. And I'm wait for picture samples
'Coz it give more explanation to me as my english is poor

[bogolisk]

+1

I'm so confused about that whole colourful mess: LoCA, PP, etc.

I hope some one (like Orio, Arkuu, Chris, etc.) would give a nice explanation.

[Laurentiu Cristofor]

OK, I went through my shots and I extracted some samples for the categories of color fringing I listed before. These are all unprocessed 100% crops and I kept them small on purpose so you don't have to scroll forever just to watch CA samples


Bokeh fringing (edit: aka longitudinal chromatic aberrations=LoCA)

This shows as green fringing behind focal plane (upper part) and purple-reddish fringing in front of it (lower part). They disappear in the focal plane, but DOF is really thin in these shots.

Super Takumar 50/1.4


Pentax FA 100-300/4.7-5.8


This is from the same shot as above, but from behind the focus plane, to show the green fringing in its splendor:


And another shot - green on the sand above, purple on the insect leg below:


Cosina 55/1.2@f/4

[Edit note: 2011/12/06 - I used to think this is purple fringing, but it's actually bokeh fringing (LoCA) in front of the focal plane:]



Lateral chromatic aberrations

This is worse towards the edges.

Samyang 8/3.5 fisheye

Upper-left corner shows a lot:


But center looks very good:



Purple fringing

[Edit note: 2013/05/13 - I now realized all these samples also fall under LoCA - I don't really have any example of purple fringing.]

I left the worse for last. I hate this. Keep in mind that these are very mild samples - I usually don't keep shots in which PF is worse than this, so I can't show you the peak of this abomination.

Tamron adaptall SP 60-300/3.8-5.4 (edit: This actually looks worse because of a WB issue - the BBAR coating of Tamron adaptall lenses is confusing the AWB feature of modern cameras with the effect of accentuating purplish tints)


Tamron adaptall SP 300/5.6

Note that this also shows bokeh fringing on the wings:


Surprisingly, the SP 60-300 zoom seems to have less PF than the SP 300 prime. One for the zooms I guess.

Of course, at 100% we're pixel peeping, but this is not about criticizing lenses, only about showing samples of aberrations manifesting themselves as color fringing.

Hope this helps. And please correct me if I'm wrong in the labeling.

[Edit note: 2011/12/06 - the original PentaxForums urls for the images had changed, so I updated this post with the current ones. I also made a few corrections and additions marked as edits based on my current evaluation of this subject.]

[Edit note: 2013/05/13 - PentaxForums keeps changing the urls. In case they keep changing, here is the folder where all the samples are available: http://www.pentaxforums.com/forums/members/21910-laurentiu-cristofor/albums/2119-color-fringing-samples/]

[blende8]

I think you got this right (from my amateur perspective).
I would add that the third variety is the classic aberration, because it appears within the plane of focus.

The first is the most controversially discussed one. Some say that it is a lens-only issue; some say it is a sensor-only issue, but most probably it is a combination of both. The lens is definitely involved. Someone from Zeiss told me that it has to do with the UV (and to a lesser degree IR) parts of the light that are not completely suppressed. Normally they are enough suppressed to not contribute to the image, but if the light intensity is extremely high even 0.1% becomes visible. Since the optical system is not perfectly corrected for UV light, it is slightly out of focus and creates the colored borders.

[Orio]

I repeat, I am no phisicist, but I am convinced that it is wrong to say that you can speak of chromatic aberration only when an object is in focus.
I will look for the opinion of a knowledgeable person.

[visualopsins]

Thank you blende8! I think you are correct here to identify and include UV factor. The "haze" that cannot be seen with eyes but appears in photos, which is reduced by using "UV/Haze" filter. This may also be cause of 'flare bloom' I described in earlier post.

[Laurentiu Cristofor]

[Laurentiu Cristofor]

[poilu]

a sample of sensor bloom
it appear only where the sensor is overcharged (overexposed),
it is called sensor bloom because it doesn't appear on negative who cannot get overcharged

[blende8]

[Laurentiu Cristofor]

This article also has some good samples and descriptions: http://toothwalker.org/optics/chromatic.html. Interesting description for LoCA. I don't seem to have experienced that too often - i.e. purple fringing that can turn into green fringing if focused slightly differently (see first samples).

poilu - thanks for the sample of sensor bloom. I suppose the center of the lights is overexposed and that's why it comes out white instead of showing the glass color. Which lens took that shot?

[gearsNcogs]

[AhamB]

[poilu]

[LucisPictor]

Some really good links:

http://en.wikipedia.org/wiki/Lens_(optics)#Aberrations

http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/aberrcon.html

http://www.cartage.org.lb/en/themes/sciences/physics/optics/Optical/Lens/Lens.htm

http://wps.aw.com/wps/media/objects/877/898586/topics/topic12.pdf

http://www.britannica.com/EBchecked/topic/430511/optics/37971/Lens-aberrations

[visualopsins]

Courtesy of the publisher, John Wiley & Sons, Inc., a couple of complete chapters from the 6-volume multi-K$US bible of lens design, in pdf!.

Chapter 29 "Aberrations": http://media.wiley.com/product_data/excerpt/95/35274037/3527403795.pdf

Chapter 36 "Human Eye": http://media.wiley.com/product_data/excerpt/09/35274038/3527403809.pdf

Lots of mathematics, lots of optical physics, lots of colorful illustrations!

(re-post. with forum search broken I can't find original )

[Laurentiu Cristofor]

I've looked over most of these links and they don't cover chromatic aberrations in particular, neither do they have practical examples. What I want to know is what the different types of fringing are called.

[vilva]

[vilva]

[Laurentiu Cristofor]

[Laurentiu Cristofor]

[Laurentiu Cristofor]

The original samples have disappeared for some reason - you can still find them here though:

http://www.pentaxforums.com/forums/members/laurentiu-cristofor-albums-color-fringing-samples.html

I just wanted to add an errata - I was reminded of it in a recent thread: the Cosina sample is actually not PF, but LoCA - I examined more carefully the images and realized it only showed in front of the focal plane and that it changed to green fringing after that. The PF examples using Tamron are good though.

I collected my recent thoughts on this topic here:

http://laurphoto.blogspot.com/2011/11/chromatic-aberrations.html

[taunusreiter]

color fringing can be caused by coma or by longitudinal chromatic aberrations (German: Farblängsfehler).

The first should be quite easy to correct for an optical designer. The latter isn't that easy. First, you have to correct the errors with objects in focus, but that don't mean that the objects out of focus are corrected as well. With a zoom lens this is quite impossible.

If you don't have any color fringing it's probably an apochromatic corrected lens.