[i83N]

Having couple of FF lenses I noticed that they have much more CA than apc ones on digital but les on film. My question is; is that because they have bigger image cycle or because counting is different?

[Na Horuk]

Um.. well.. if the lenses are older design (with older generations of coating) this might mean it has more CA than modern designs and coatings. More expensive lenses usually also have better CA performance. And primes/fixed focal length lenses should perform better than zoom lenses (although, modern zoom lenses have almost caught up)
The other thing is that the digital medium is slightly different. For example, the sensor is slightly reflective. It also captures colours differently. And finally, with digital photos its easy to look at 300% zoom and notice every "wrong" pixel. With film photos, you probably don't look at them at such magnification.

The good news is that with digital photos you can post process and use lens profiles to reduce quite a lot of CA.

Edit: Also, Pentax lenses are pretty good when it comes to lateral CA. Not so great when it comes to axial/longitudinal CA, though.

[Mazhe]

What kind of CA are you seeing? The red/green ghosts of transversal chromatic aberrations (TCA) or purple fringing? Are you using in-body automatic corrections?

Older lenses are actually almost always better on the TCA side, because post processing is expected nowadays, but are more prone to purple fringing.

[i83N]

I'm talikning about fa 50mm f1,4 and fa 43mm.

What kind of CA are you seeing? The red/green ghosts of transversal chromatic aberrations (TCA) or purple fringing? Are you using in-body automatic corrections?

Older lenses are actually almost always better on the TCA side, because post processing is expected nowadays, but are more prone to purple fringing.

Blue and yellow CA
Don't use in-body

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Last edited by i83N; 04-10-2014 at 05:00 AM.

[lytrytyr]

I'm talikning about fa 50mm f1,4 and fa 43mm.

The Photozone review of the FA 43 notes that
"Lateral chromatic aberrations (color shadows at harsh contrast transitions) are relatively pronounced for a "normal" lens with an average CA pixel width around 1.4px on the average at the image borders. This is not a big deal but the (younger) DA 40mm f/2.8 Limited did a better job here."

Pentax SMC FA 43mm f/1.9 Limited - Lab Test / Review - Analysis

[i83N]

The Photozone review of the FA 43 notes that
"Lateral chromatic aberrations (color shadows at harsh contrast transitions) are relatively pronounced for a "normal" lens with an average CA pixel width around 1.4px on the average at the image borders. This is not a big deal but the (younger) DA 40mm f/2.8 Limited did a better job here."

Pentax SMC FA 43mm f/1.9 Limited - Lab Test / Review - Analysis

Yes it's not a problem for me, just curious

[stevebrot]

What kind of CA are you seeing? The red/green ghosts of transversal chromatic aberrations (TCA) or purple fringing?

...or the blue/yellow of halo of longitudinal CA (LoCA) which is similar to, but different and distinct from purple fringing.


Some degree of TCA and/or LoCA is common even on modern lenses and is not any more common on vintage glass. Purple fringing, on the other hand is not CA per se since it does not exist on film images.* PF does cause false color, but it is not due to an optical aberration of the lens that results in different wavelengths focusing on different points at the focal plane (i.e. CA). The color of LoCA changes with focus while PF does not. LoCA also does not "bloom" or "spread" in the same many as severe PF.

Many vintage lenses tend to invoke PF more easily from a digital sensor than modern designs hence the generalization regarding PF an old glass. My experience has been that some do and some don't. Theory is that PF is caused by position, size, and geometry of the rear element causing a malignant spread of false signal through the sensors microlens grid...or something like that.


Steve

* I can fairly reliably generate PF with a couple of my lenses on digital, but have never seen the same with film images from the same lenses

[Digitalis]

Theory is that PF is caused by position, size, and geometry of the rear element causing a malignant spread of false signal through the sensors microlens grid...or something like that.

Interesting explanation, however I have used lenses on older digital SLR cameras without microlenses and PF doesn't seem to be any better- or worse.The funny thing is that they handled vignetting somewhat better than microlens equipped sensors do now.

[tim60]

Another factor is that until the mid 70s it was only practical to manufacture spherical surfaces, and the aspherical surfaces that followed, and have become more common enable additional optical design to reduce nasty effects of all kinds including CA.

[i83N]

Another factor is that until the mid 70s it was only practical to manufacture spherical surfaces, and the aspherical surfaces that followed, and have become more common enable additional optical design to reduce nasty effects of all kinds including CA.

But i see CA in lenses made not in 70s

[kh1234567890]

Interesting explanation, however I have used lenses on older digital SLR cameras without microlenses and PF doesn't seem to be any better- or worse.The funny thing is that they handled vignetting somewhat better than microlens equipped sensors do now.

This is to me the most plausible explanation of PF.

[stevebrot]

This is to me the most plausible explanation of PF.

LoCA? Yep, I have heard that too and many cases of LoCA are referred to as PF. After all, there is a fringe and it is purplish, right? Unfortunately, there is PF that is not LoCA, that being the kind where there is a bloom or where the fringing is not associated with plane of focus. The "white wedding dress on a sunny day" is probably the most alarming case.

I first became acquainted with PF when I bought my Canon G2. Back in those days it was considered to be a sensor issue and testing involved a flash photo of candy wrappers (crumpled cellophane). Before then, I had shot film for 30+ years and while I was familiar with both lateral and longitudinal CA, nobody talked about PF. It simply doesn't exist in film photography.

I suppose one of these days I should probably do some comparison photos. I have two lenses that are supposed to be notorious for PF (FA 35/2 and FA 77/1.8 Limited) and I also have several K-mount film bodies. I follows that if I can produce PF on digital, the same lens on a film body should also show it. Assuming, of course, that PF is a lens issue.


Steve

BTW...I tend to follow Falconeye's line of reasoning in the same thread. I also agree with him that lateral CA is the more important issue since it degrades sharpness across the frame.

[kh1234567890]

After all, there is a fringe and it is purplish, right? Unfortunately, there is PF that is not LoCA, that being the kind where there is a bloom or where the fringing is not associated with plane of focus.

It was more the overload bit rather than LoCA. Having scanned in hundreds of my old colour negs at a resolution similar to digital (2700 dpi) I don't recall seeing one where purple fringing was obvious. And yet it was one of the first things that bothered me when I started playing with digital.

PF seems to be caused by the three Bayer array colour channels saturating in a different way - RawDigger pixelpeeps of a PF twig against the sky, no demosaicing (except on the composite). Purple indicates saturated areas in the bottom two

[stevebrot]

It was more the overload bit rather than LoCA. Having scanned in hundreds of my old colour negs at a resolution similar to digital (2700 dpi) I don't recall seeing one where purple fringing was obvious. And yet it was one of the first things that bothered me when I started playing with digital.

PF seems to be caused by the three Bayer array colour channels saturating in a different way - RawDigger pixelpeeps of a PF twig against the sky, no demosaicing (except on the composite). Purple indicates saturated areas in the bottom two

Fascinating...(in my best Spock manner). Do you think this is an artifact of the image processing engine?


Steve

[kh1234567890]

Fascinating...(in my best Spock manner). Do you think this is an artifact of the image processing engine?

That is just the RAW file data from a K-7, no demosaicing or processing done on the three RGB channels (the G2 was same as the G1). As close to what the sensor readout is as you can get. The lens was M135/3.5. The (somewhat uninspired) photo is here, CA corrected and defringed. The RAW is here.