[Kirivon]

If an artifact can be removed as part of the raw conversion, I'm not really seeing why it is a problem. Of course, I've also never seen PF off my 77 either.

Under the right (wrong) lighting, results such as this are common:



In this crop, you can see the PF on the highlights of the salt and pepper shakers quite clearly. Also, there is green fringing and at the top edge of the tablecloth, and red fringing on the bottom napkin. I haven't figured out a way to neutralize these LOCAs in post processing, short of going full out and de-saturating the edges with masks in photoshop. This lens is sort of a savant of my lineup; if you are mindful of its weaknesses, its strengths make up for it by far. For the scene above I simply moved the shakers so that they weren't directly under the light.

[stevebrot]

In my humble opinion, this is longitudinal chromatic aberration, not purple fringing. Longitudinal CA typically shows green fringing behind the plane of focus and purple fringing in front of the plane of focus, like in this picture...

Good point. It may well be lo-CA.

The photozone review of the FA 77/1.8 Limited has a good discussion regarding PF and this lens along with some really good pictures of what PF looks like.

Pentax SMC-FA 77mm f/1.8 Limited Review / Test Report

Steve

[stevebrot]

...I haven't figured out a way to neutralize these LOCAs in post processing, short of going full out and de-saturating the edges with masks in photoshop...

I have had pretty good luck with the lat-CA and lo-CA sliders in Lightroom. I don't know whether these are supported in ACR outside of Lightroom.

Steve

[Digitalis]

I have had pretty good luck with the lat-CA and lo-CA sliders in Lightroom. I don't know whether these are supported in ACR outside of Lightroom.

Steve

they are in ACR, but for everything else I would doubt it. there are times when I wish that the FA77 would only have the transverse chromatic aberration that the K 50mm f/1.2 has - it's always red/blue fringing in the corners and is very simple to remove. Purple fringing is a real pain in the soft parts to remove, and in some situations it's impossible to remove; which is the annoying thing about lenses with this particular problem. Even Leica and Zeiss lenses suffer from PF it at the wider end of their aperture settings, so it isn't really just a pentax lens design thing.

---

Last edited by Digitalis; 11-30-2009 at 06:31 AM.

[stevebrot]

...Purple fringing is a real pain in the soft parts to remove, and in some situations it's impossible to remove; which is the annoying thing about lenses with this particular problem. Even Leica and Zeiss lenses suffer from PF it at the wider end of their aperture settings, so it isn't really just a pentax lens design thing.

No arguments here!

The tendency to have PF is not related to price or pedigree. Of the lenses that I own, only three have this issue:

• Pentax DA 18-55/3.5-5.6
• Pentax FA 77/1.8 Limited
• KMZ MC Zenitar 16/2.8 Fisheye

Of the three, the 77 Limited is by far the mildest offender. (I know...photozone indicates PF for the FA 35/2...though I have never had a problem...)

As noted a couple of times in the previous comments, some PF with current digital cameras is a characteristic of the FA 77 and represents a trade-off to a potential purchaser. A lot depends on your style of shooting and choice of subjects. For me with my choice of subjects and lighting, PF has seldom been an issue.

Steve

[Blue]

No arguments here!

The tendency to have PF is not related to price or pedigree. Of the lenses that I own, only three have this issue:

• Pentax DA 18-55/3.5-5.6
• Pentax FA 77/1.8 Limited
• KMZ MC Zenitar 16/2.8 Fisheye

Of the three, the 77 Limited is by far the mildest offender. (I know...photozone indicates PF for the FA 35/2...though I have never had a problem...)

As noted a couple of times in the previous comments, some PF with current digital cameras is a characteristic of the FA 77 and represents a trade-off to a potential purchaser. A lot depends on your style of shooting and choice of subjects. For me with my choice of subjects and lighting, PF has seldom been an issue.

Steve

My FA 77mm just arrived via UPS. My copy was made in Japan. Perhaps its the Vietnam versions that are susceptible to PF.


(j/k I don't want to be the source of an urban legend)

[HermanLee]

This is going to sound sort of hokey, but given a back-lit tree branch, yellow/blue CA will generally show yellow (often vague) on one side of the branch and blue on the other. PF, on the other hand, will be blue or purple on both sides. CA is also visible as a color band extending a set distance (x number of pixels) from a light/dark boundary. PF is of inconsistent width and will span gaps. And finally...CA is generally correctable in Lightroom or ACR using the CA correction feature. PF does not correct except by de-saturating the blue and/or purple channels. (At this point it is important to note that CA is actually present throughout the frame, not just where you can see it. The result is a generalized decrease in sharpness both with color and b&w photos that improves when the CA is corrected in PP.)
...
Steve

Hi Steve,

Sorry for the late reply. Just got back from long Thanksgiving vacation and been busy at work.
That's a very extensive explanation yet simple enough to understand. I guess you have a talent to be a teacher
Thanks for taking your time to explaining this difference. Now I understand where and what to look for CA or PF.

[HermanLee]

In my humble opinion, this is longitudinal chromatic aberration, not purple fringing. Longitudinal CA typically shows green fringing behind the plane of focus and purple fringing in front of the plane of focus, like in this picture, linked from Photozone.de (this is from the review of the DA*200/2.8, another Pentax lens which has a real problem with purple fringing and longitudinal CA):

Cheers!

Abbazz

Wow, how many type of CA that exist?
At first I thought there were only CA against PF but now there is another type of CA.
But thanks for pointing this out, Abbazz.
One more thing to learn today.

[HermanLee]

Hi guys,

I have a question for those who knows and already tried this. (Pls don't make assumption )

Do you see purple fringing on your photos in an extreme contrast condition taken with Pentax FA 77mm/1.8 Ltd on your 35mm FILM CAMERA ?

The reason I asked this because I can see a little bit purple fringing on extreme contrast photo taken with my K20D and FA 77Ltd.
Not that it's a big deal to me because I can always remove it in PP.
What makes me curious is after reading the review at photozone.de. Here is the quote about purple fringing:

"Please don't let you put off by this problem though. This happens only in extreme contrast situations when the bright portion is at or beyond the contrast latitude capabilities of the sensor. "

Photozone tested the lens using K10D and it seems from the quote, the problem is with the digital sensor capability on K10D.
So, does anyone know about this and probably made a test with their film camera?

Thanks in advance.

So back to my original questions, regarding whether the PF can also be seen in film or not and whether the statement from Photozone about the current sensor's capability as being the culprit, it seems that Photozone's conclusion is not correct.

Based on the answers here, it seems not because of the sensor's limitation but more of a lens design's limitation.
Unless there is a limitation of the film capability to cause PF.
Could it be possible that PF from FA 77Ltd only happen on certain type/brand of film?
If yes, what brand/type of film that will not show PF of FA 77 Ltd at all?

Thanks,

[stevebrot]

So back to my original questions, regarding whether the PF can also be seen in film or not and whether the statement from Photozone about the current sensor's capability as being the culprit, it seems that Photozone's conclusion is not correct.

Based on the answers here, it seems not because of the sensor's limitation but more of a lens design's limitation.
Unless there is a limitation of the film capability to cause PF.
Could it be possible that PF from FA 77Ltd only happen on certain type/brand of film?
If yes, what brand/type of film that will not show PF of FA 77 Ltd at all?

Thanks,

There are a number of opinions regarding PF on this forum and a number of theories at various places on the Web. The lens/camera manufacturers are keeping mum regarding causes, though it enough to say that PF has been the bane of digital photography from the beginning.

Here is the general situation as I understand it:

• Most, if not all, lenses can invoke PF on current generation digital sensors
• Some lenses are worse than others regardless of manufacturer
• "Digital" lenses are no better (DA* 15/4 being a good example)
• The presence of PF on film is debatable. I have never seen a convincing example, but am keeping my eyes open and will post it to this forum when/if I see it. With any luck, I will be able to do a direct comparison using both the K10D and one of my film cameras.
• Probably the best evidence for the lack of PF on film is the fact that older film users (like myself) had never heard of PF prior to our digicam purchases. CA, yes...PF, no.
• Some believe that PF is just plain old lateral CA. This notion is compelling since severe lateral CA looks a lot like PF.
• Others believe that PF is CA or flare of the microlenses on the sensor
• Still others believe that PF is a sensor artifact of unknown cause

I, for one, an unwilling to accept the notion that PF is a defect in lens design per se, though it is obvious that lens design must be a contributing factor.

Steve

[egonomic]

There are a number of opinions regarding PF on this forum and a number of theories at various places on the Web. The lens/camera manufacturers are keeping mum regarding causes, though it enough to say that PF has been the bane of digital photography from the beginning.

Here is the general situation as I understand it:

• Most, if not all, lenses can invoke PF on current generation digital sensors
• Some lenses are worse than others regardless of manufacturer
• "Digital" lenses are no better (DA* 15/4 being a good example)
• The presence of PF on film is debatable. I have never seen a convincing example, but am keeping my eyes open and will post it to this forum when/if I see it. With any luck, I will be able to do a direct comparison using both the K10D and one of my film cameras.
• Probably the best evidence for the lack of PF on film is the fact that older film users (like myself) had never heard of PF prior to our digicam purchases. CA, yes...PF, no.
• Some believe that PF is just plain old lateral CA. This notion is compelling since severe lateral CA looks a lot like PF.
• Others believe that PF is CA or flare of the microlenses on the sensor
• Still others believe that PF is a sensor artifact of unknown cause

I, for one, an unwilling to accept the notion that PF is a defect in lens design per se, though it is obvious that lens design must be a contributing factor.

Steve

Purple fringing is longitudinal chromatic aberration, and would only be absent on a 'normal' (non-apo, reasonable apertures) lens with perfectly corrected coma and spherical aberration, and even then only within the plane of focus - this is well established even in old optics bibles such as Optics by Eugene Hecht. The use of low dispersion glass minimises longitudinal chromatic aberration. Purple fringing only occurs in front of the plane of perfect focus (the area can appear in focus but is in front of the flat plane of perfect chromatic convergence).

Lateral CA is not purple fringing. Lateral CA is almost always yellow/blue or red/cyan in those pairs on opposite sides of high contrast transitions and can occur within the plane of focus with non-APO lenses.

Purple fringing is less visible on film, but is still present, I have observed it even with very good lenses (Leica 50mm Summilux E60) on film at larger apertures.

The Voigtlander 180mm APO-Lanthar and Coast Optics 60/4 do not display purple fringing at the magnifications of current sensors, ever.

[Blue]

. . .
The Voigtlander 180mm APO-Lanthar and Coast Optics 60/4 do not display purple fringing at the magnifications of current sensors, ever.

For $4500, a lens better be better than very good. It should be 5x better than a 60mm Tomioka or at least walk on water. Besides, its a macro and the 180mm is another ballgame. I'm certainly not inclined to replace my Tammy 180mm f2.5 with an f4 lens. Besides, the former is for IR/UV work. There are a couple of special Pentax 85mm f1.4 lenses out there for that.

Purple fringing is less visible on film, but is still present, I have observed it even with very good lenses (Leica 50mm Summilux E60) on film at larger apertures.

One of the original points brought up is that photzone went out of the way to force the FA 77mm to pf but didn't on the DA 70mm. Regardless, both these lenses are compact, auto-focus and well made and quite good optically.

[Lowell Goudge]

Purple fringing is longitudinal chromatic aberration, and would only be absent on a 'normal' (non-apo, reasonable apertures) lens with perfectly corrected coma and spherical aberration, and even then only within the plane of focus - this is well established even in old optics bibles such as Optics by Eugene Hecht. The use of low dispersion glass minimises longitudinal chromatic aberration. Purple fringing only occurs in front of the plane of perfect focus (the area can appear in focus but is in front of the flat plane of perfect chromatic convergence).

While I do not dispute that longitudinal CA produces purple fringing in OOF zones in front if ideal focus, I believe there is a destinction between longitudinal CA and the "blooming" of purple surrounding subjects typically in strong backlit situations, that is attributed to sensor design

[farfisa]

You're also not going to see a lot of purple fringing on the FA77 by f/4.

[Blue]

You're also not going to see a lot of purple fringing on the FA77 by f/4.

Not only is it slow, its a UV macro lens.