Testing longitudinal (axial) chromatic aberration (1 Viewer)

Jessie-66 · Dec 15, 2020

Hello friends,

I do lateral chromatic aberration (CA) testing when comparing binoculars on the edges of nearly black roofs, satellite antennas of the same color, power lines and poles against bright but gray skies.

How or with which observation objects can I check longitudinal (axial) CA?

Notes:
I do not have a tripod and booster. I have never been able to see axial CA consciously.
Yes, I know this is a luxury problem of bean counters and hair splitters, I should be happy not to notice every imperfection. But it still interests me. ;-)

Best regards
Jessie

Another thought from me:
Good mid-range binoculars are excellent for observing nature, and you can learn a lot about optics from their little, practically irrelevant imperfections (aberrations) if you research them and related topics in the WWW.

Maljunulo · Dec 15, 2020

Once you notice a "defect" or an "imperfection" you will forever be aware of it and it will plague and annoy you to no end.

To paraphrase: "Be careful what you look for."

Jessie-66 · Dec 15, 2020

You are very right, but this is just about technology, binoculars, I have had to deal with imperfect technology all my professional life, sometimes struggling. I love some people with obvious weaknesses, maybe that's why? I also like things with imperfections, modern mid-range binoculars, porro prism binoculars. Just by having a particularly nice feature that makes them stand out from the gray crowd, different from the mainstream, they must have. Look, my new Hawke APO has a particularly wide field of view, the focus is too smooth, too fast for my taste. I call it "my little Sensibelchen" for that reason. The german word "Sensibelchen" can not be correct translated, means something like "extremely sensitive, mentally very easily hurt person".

During my nature observations, optical flaws hardly bother me, rather ergonomic weaknesses. The beauty of nature wins over every optical nitpicking, even makes it ridiculous.
But I am still curious, technology was my profession and vocation.

Omid · Dec 15, 2020

Jessie,

Welcome to the binocular forum. Before you investigate longitudinal chromatic abberation (LCA) produced by various binoculars. You might want to learn about LCA in your own eyes. Did you know that human eye lens has a very strong longitudinal chromatic abberation (approximately 2 diopters)? Several studies have tried to "improve eye acuity" by adding an achromatizing lens in front of the eye but they have all failed to produce "super vision". Interestingly, new research indicate that LCA is used by the eye to accommodate on near objects (see, for example, Kruger et. al, Vision Research, Vol. 33 No. 10, 1993).

You eyes are not a camera and your retina is not a film or a CCD surface. Longitudinal chromatic abberation of your binoculars do not have the same effect on your visual perception as you might expect from photographic experience. This is not to say that LCA doesn't matter in binoculars. It does. But the human eye is very forgiving in this respect.

-Omid

Sterngucker · Dec 15, 2020

It is very easy to get a bit anal about these things, so I am with Maljunulo in post #2 on this.

Jessie-66 · Dec 15, 2020

Both Odysseus and Orpheus managed to sail past Siren Island without succumbing to her beguiling song.
When the Argonauts came close to Siren Island, Orpheus was able to drown out her song with his lyre. Almost the entire crew came out of the adventure in one piece. Only Butes nevertheless heard their beguiling voices, jumped from the ship and swam toward the island, but was rescued just in time by Aphrodite, who had him carried by the waves to Lilybaion in Sicily.[20]
According to Homer, who provides the oldest literary tradition of the Siren Saga, the two Sirens, who lived on an island, attracted sailors not only by their enchanting voice, but especially by their ability to know and reveal everything that happened on earth. If the sailors followed them to the island, they were lost and died. Their exact fate is not stated in the Odyssey and only pale bones of decayed people are reported. Apparently they did not serve as food for the Sirens. Nevertheless, Odysseus wanted to hear the sirens' song out of curiosity. On the advice of the sorceress Kirke, he had his companions' ears sealed with melted wax and tied himself to the mast of the ship. Thus he could hear the sirens' song, which promised to tell him the future during a short visit, but when he was enraptured and wanted to follow, his companions tied his ropes even tighter as previously agreed. Once out of earshot, the spell lost its effect.
(automatic translation from german Wikipedia)

Sirene (Mythologie) – Wikipedia

de.wikipedia.org

;-)

Sterngucker · Dec 15, 2020

I guess this is where I get off this train. Hasta la vista muchachos.

AlanFrench · Dec 15, 2020

I am skeptical that even 10x is enough magnification to reveal secondary color (longitudinal chromatic aberration). In achromatic refractors it generally reveals itself at higher magnifications.

Plus, under the bright conditions that might tend to reveal secondary color, most binoculars are significantly stopped down by our eye's pupil, My 7x42s may have a 6mm exit pupil, but under bright conditions my eye is only open to perhaps 2mm and I am using only 14mm of the aperture. I'm no longer seeing the aberrations of perhaps a 42mm f/3.6 lens, I am seeing those of a 14mm f/10.7 lens.

I am also firmly in the "My binoculars provide fine, detailed, entirely satisfactory views of birds - don't look for trouble" camp.

Clear skies, Alan

elkcub · Dec 15, 2020

Jessie-66 said:
Both Odysseus and Orpheus managed to sail past Siren Island without succumbing to her beguiling song.
When the Argonauts came close to Siren Island, Orpheus was able to drown out her song with his lyre. Almost the entire crew came out of the adventure in one piece. Only Butes nevertheless heard their beguiling voices, jumped from the ship and swam toward the island, but was rescued just in time by Aphrodite, who had him carried by the waves to Lilybaion in Sicily.[20]
According to Homer, who provides the oldest literary tradition of the Siren Saga, the two Sirens, who lived on an island, attracted sailors not only by their enchanting voice, but especially by their ability to know and reveal everything that happened on earth. If the sailors followed them to the island, they were lost and died. Their exact fate is not stated in the Odyssey and only pale bones of decayed people are reported. Apparently they did not serve as food for the Sirens. Nevertheless, Odysseus wanted to hear the sirens' song out of curiosity. On the advice of the sorceress Kirke, he had his companions' ears sealed with melted wax and tied himself to the mast of the ship. Thus he could hear the sirens' song, which promised to tell him the future during a short visit, but when he was enraptured and wanted to follow, his companions tied his ropes even tighter as previously agreed. Once out of earshot, the spell lost its effect.
(automatic translation from german Wikipedia)

Sirene (Mythologie) – Wikipedia

de.wikipedia.org

;-)

"Curiosity killed the cat,
But satisfaction brought it back."

Ed

NDhunter · Dec 16, 2020

Omid: I agree with you, your post seems on solid ground, everyone's eyes are different, and they are not cameras.

Sternucker, I also agree with you, Jessie has fallen off the deep end....this forum is not a fairytail.

Jerry

tenex · Dec 16, 2020

Jessie-66 said:
How or with which observation objects can I check longitudinal (axial) CA?
....I have never been able to see axial CA consciously.

To get back to your basic question: I don't think one can, it's not a distinctive effect like lateral CA. It manifests as a muddying of focus, and would be hard to distinguish from other aberrations that also reduce sharpness, except perhaps with specialized test equipment. (Is that the answer you were looking for?)

Jessie-66 · Dec 16, 2020

Thanks to all. I learned that due to the low magnifications of binoculars and reduced pupil diameter in bright light, longitudinal CA is not directly detectable, i.e., by color changes. This aberration leads to (further) blur, which is indistinguishable from blur caused by other aberrations without special test equipment.
And your answers also have a small psychological effect: I don't feel like a bad observer ;-)

Ed (elkcup), you made me laugh about the satisfactory resurrection of the courious cat. I wish the cat many new and curious lifes.

Patudo · Dec 19, 2020

AlanFrench said:
I am also firmly in the "My binoculars provide fine, detailed, entirely satisfactory views of birds - don't look for trouble" camp.

Clear skies, Alan

Wise words those. I recall it was Steve C (I think?) who mentioned that he'd taught himself how to see chromatic aberration and once he had, he could not unsee it. I don't look into (as opposed to looking through) my binoculars, look at them from the wrong end, etc.

Jessie-66: I used to visit a place, now sadly cut off by the virus, where looking through a good pair of binoculars made you feel as though you were seeing with the eyes of Zeus. Or Horus.

Jessie-66 · Dec 19, 2020

Patudo said:
Jessie-66: I used to visit a place, now sadly cut off by the virus, where looking through a good pair of binoculars made you feel as though you were seeing with the eyes of Zeus. Or Horus.

Your text builds me up again, about NDhunter's obvious ignorance with devaluation of Homer's Iliad and Odyssey, their impact on several languages, international science and art I am still amazed and frustrated. Perhaps all hope is not lost, therefore:

Iliad - Wikipedia

en.wikipedia.org

Fairy tale? No, world literature, general education of many people, peoples!
For inadequate education many people can not do anything, but devaluation of individual unknown great works and short references, excursions to them? In forum there is more than enough off topic, opinions without facts ...

tenex · Jan 2, 2021

tenex said:
To get back to your basic question: I don't think one can, it's not a distinctive effect like lateral CA. It manifests as a muddying of focus, and would be hard to distinguish from other aberrations that also reduce sharpness, except perhaps with specialized test equipment.

This issue has been nagging at me because I felt I answered a bit hastily. I've never seen longitudinal CA, and had only read about it requiring fine-tuning of a camera's autofocus with certain lenses, so I explained it away as just a minor form of blurring. I finally searched a bit and found that it's not.

LoCA occurs across the field rather than mainly toward the periphery, and can indeed involve false color as well as blurring. See the first photo below from a lens review at photographylife.com. I haven't experienced this myself, but I don't shoot closeups of bright objects with fast lenses wide open. The second photo with more depth is from Wikipedia, clearly showing purple in the foreground and green in the background.

Stopping down reduces LoCA, so presumably your pupil eliminates it for you in daylight, at least with reasonable quality binoculars. Has anyone ever seen this effect in the cheapest ones?

Jessie-66 · Jan 2, 2021

To complement tenex' post 2 other photos from the German Wikipedia on axial CA (photography):

Chromatische Aberration – Wikipedia

de.wikipedia.org

Longitudinal chromatic aberration reduced by stopping down, lateral CA is retained:

Chromatische Aberration – Wikipedia

de.wikipedia.org

(Longitudinal chromatic aberration in German language: "Farblängsfehler", lateral CA "Farbquerfehler".)

As a technical interested person, according photos from German Wikipedia I searched myself before opening the thread: Dark roof edges with great depth. Problem: I only saw lateral CA. I also looked in close-up: dark grey tiles with light grey grout, with not so bright artificial light (ceiling lamp) or light through the opposite window, standing and squatting. No color changes.

The art, imho, is to choose a suitable observation object with great depth and suitable colours/contrasts. And cheap, bad binoculars as tenex said. Or magnification of my 8x and 10x bins is too low.

Testing longitudinal (axial) chromatic aberration (1 Viewer)

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