[popo]

[quote name='PuxaVida' timestamp='1291465457' post='4754']

Did you also try - both aperture known & unknown- @ ISO 200 or higher?

[/quote]

I have now. Only did ISO800 at f/2. Same thing happens as for ISO100.

[Brightcolours]

[quote name='popo' timestamp='1291478894' post='4758']

Turning that around, why is there a need for a different mechanism when LoCA seems to me adequate to describe both. I haven't seen anything yet that suggests it isn't.





Full test output





Crop from bottom of top-middle.





Crop from top of bottom-middle.



Anyway, here's the result of my test. I created a test image with relative levels of 0% background, 25% for lower star backgrounds, and 100% for upper star backgrounds. Put the EF 85mm f/1.8 on the 450D, and manually focused on the vertical point of the middle stars at f/1.8. The lower contrast stars at the bottom show the expected regular LoCA colours, red/magenta-ish in front of the focal plane, and green-ish behind. Looking at the top 3 there's a lot of magenta "PF" on and in front for the focal plane. It's more interesting behind the focal plane, with a tiny amount of blue before going green mixing into yellow. The green/yellow thing seems dependant on the direction of contrast change with defocus.



This was obtained with one lens in one shot. It shows LoCA and PF happening, the only difference between them is the lightness of the region.



I'm open to discussion if there may be anything I've overlooked or misinterpreted here. Different lenses may exhibit different colours so could have the same test performed to see if that remains the case. I can repeat this for my other lenses on request.

[/quote]

No, it does not show PF and LoCA happening. It only shows LoCA happening (magenta blur to the front, green blur to the back).

All lenses that show LoCA (most wider aperture lenses and macro lenses) have exactly the same thing: Green blur on one side of the focal plane, purple on the other side.



Check photozone's more current reviews to verify that.



PF only is one colour, and only around very bright areas. It also usually only radiates to one side of bright "holes", where LoCA is in the whole blur/bokeh.



BTW: The PF examples I have... the top one, from the Sony 16mm f2.8 fisheye, does not seem to be PF now that I looked at it again. It seems to be NORMAL (La) CA, with green edges going from the "dark" into the bright, and purple edges going from the bright into the dark. It was a corner crop, so I am pretty sure that is normal CA and not PF (and certainly not LoCA).

[popo]

[quote name='Brightcolours' timestamp='1291480107' post='4760']

No, it does not show PF and LoCA happening. It only shows LoCA happening (magenta blur to the front, green blur to the back).

All lenses that show LoCA (most wider aperture lenses and macro lenses) have exactly the same thing: Green blur on one side of the focal plane, purple on the other side.



Check photozone's more current reviews to verify that.



PF only is one colour, and only around very bright areas. It also usually only radiates to one side of bright "holes", where LoCA is in the whole blur/bokeh.

[/quote]

On LoCA colours, I'm just leaving the door open to the possibility someone might have used less conventional "glass" which might result in a different style of aberration even if I've not seen one yet.



Back on PF, if it is only to one side, that sounds like lateral CA.



Does that purple stuff in the top-left of my shot not fit the typical description for PF? It's purple, it happens when it's bright, it also happens on the apparent focal plane.



Just to nail this, next time I'm out I'll try to remember the EF 85mm f/1.8 which I think we can agree does exhibit PF, and will try and find some green leaves to shoot at with various defocus and see what happens.

[PuxaVida]

I managed it also I think... The difference can be seen on red channel. With the known aperture, the image was brighter to my eyes also.



Photo was made on D700 with 50mm 1.8D, center weighted average metering. I had to use CWA metering because interestingly the body sets itself automatically to it when I twisted the lens. I shot at infinity focus towards a gray LCD screen.

[Guest]

[quote name='Brightcolours' timestamp='1291480107' post='4760']

No, it does not show PF and LoCA happening. It only shows LoCA happening (magenta blur to the front, green blur to the back).

All lenses that show LoCA (most wider aperture lenses and macro lenses) have exactly the same thing: Green blur on one side of the focal plane, purple on the other side.



Check photozone's more current reviews to verify that.



PF only is one colour, and only around very bright areas. It also usually only radiates to one side of bright "holes", where LoCA is in the whole blur/bokeh.



BTW: The PF examples I have... the top one, from the Sony 16mm f2.8 fisheye, does not seem to be PF now that I looked at it again. It seems to be NORMAL (La) CA, with green edges going from the "dark" into the bright, and purple edges going from the bright into the dark. It was a corner crop, so I am pretty sure that is normal CA and not PF (and certainly not LoCA).

[/quote]



However the article (http://toothwalker.org/optics/chromatic.html) you provided as a reference actually says that purple fringing *is* LoCA?

[Brightcolours]

[quote name='Lomskij' timestamp='1291512786' post='4767']

However the article (http://toothwalker.org/optics/chromatic.html) you provided as a reference actually says that purple fringing *is* LoCA?

[/quote]

No, it does not. As I have said (and there is plenty to be found about it) the article is talking about loCA and showing loCA (green/magenta).



There is also something ELSE to be found, that is PF.



They are two separate things, and the article only touches on PF at the end to debunk "sensor blooming" and such as being a cause for PF. Of course, some "PF"-cases can actually be attributed to loCA, the magenta part. But that then is just a case for wrongly identified PF.



In short, the term purple fringing gets used for a number of different phenomena. It gets used for LaCA where magenta shows up as one of the offending colour edges. It gets used for magenta showing up with LoCA. And it gets used for purple/blue-ish or even red-ish occurrences that are neither LoCA or LaCA. And that, according to me, is PF.



What popo showed was clearly LoCA, with a green or purple edge ALL OVER the bokeh edge parts. That is very very inherent to loCA... it is coloured bokeh. And that is very different in character to the two cases of PF is showed, they are not related to bokeh but only to light intensity seeming to "radiate" into the dark surroudings, not even and not bokeh like as with LoCA.

[popo]

[quote name='Brightcolours' timestamp='1291553467' post='4768']

There is also something ELSE to be found, that is PF.

[/quote]

Can you give some samples which show what you consider PF which, at the same time, can not be either lateral or longitudinal CA? Preferable whole images not crops which lose context.



I'm about to go an try the leaf test although as always the weather is never right when you want to go outdoors...

[Guest]

[quote name='Brightcolours' timestamp='1291553467' post='4768']

No, it does not. As I have said (and there is plenty to be found about it) the article is talking about loCA and showing loCA (green/magenta).



There is also something ELSE to be found, that is PF.



They are two separate things, and the article only touches on PF at the end to debunk "sensor blooming" and such as being a cause for PF. Of course, some "PF"-cases can actually be attributed to loCA, the magenta part. But that then is just a case for wrongly identified PF.



In short, the term purple fringing gets used for a number of different phenomena. It gets used for LaCA where magenta shows up as one of the offending colour edges. It gets used for magenta showing up with LoCA. And it gets used for purple/blue-ish or even red-ish occurrences that are neither LoCA or LaCA. And that, according to me, is PF.



What popo showed was clearly LoCA, with a green or purple edge ALL OVER the bokeh edge parts. That is very very inherent to loCA... it is coloured bokeh. And that is very different in character to the two cases of PF is showed, they are not related to bokeh but only to light intensity seeming to "radiate" into the dark surroudings, not even and not bokeh like as with LoCA.

[/quote]



Ok, let me quote that again:



"As the human eye and autofocus systems are particularly sensitive to green light, both manual focus and autofocus tend to bring the green image in sharp focus. The other colors of the spectrum are left defocused and add up to a magenta fringe. For this reason purple fringing is more common than green fringing."



To me it clearly says that PF is LoCA - just in this case you get purple fringing only, without its green counterpart.

[wim]

[quote name='Lomskij' timestamp='1291557085' post='4771']

Ok, let me quote that again:



"As the human eye and autofocus systems are particularly sensitive to green light, both manual focus and autofocus tend to bring the green image in sharp focus. The other colors of the spectrum are left defocused and add up to a magenta fringe. For this reason purple fringing is more common than green fringing."



To me it clearly says that PF is LoCA - just in this case you get purple fringing only, without its green counterpart.

[/quote]

Even toothwalker can be wrong. And we're talking optical systems of the non-living kind here.



The problem with what we call PF rather than any of the chromatic aberrations or CA like lateral chromatic aberrations or LA, LoCa, spherochromatism or longitudinal chromatic aberrations, is that due to the fact that it actually isn't a proper chromatic aberration, it can coincide with chromatic aberrations. One of the differences between LoCa, and even lateral chromatic aberrations, is that these only occur on one side of the contrast transition. PF may occur everwhere surrounding the contrast transition, plus it may occur everywhere in the image, in focus, out of focus, and anywhere from the centre to the extreme corners, whereas proper chromatic aberrations do not occur in the centre of an image, generally speaking, and LoCA=a only occurs in the OOF area of an image.



In short, chromatic aberrations have a spherical component, PF doesn't. That is the big difference.



As to exact colours: that is always hard, because colour hue and colour intensity depends on processing a lot, but also on the lenses and camera used. Generally speaking, PF is bright purple, but may be a bit more bluish, LoCa generally varies from dark red, almost brownish red, to magenta in the foreground and cyan to dark green in the background, and lateral chromatic aberrations vary from dark to bright blue to purplish blue on the inside of high contrast transitions (cente of image side) and green to green yellow to bright yellow to burnt orange on the outside of high contrast transitions (away from the centre of the image).



There is a very good example of PF in the 50L APS-C review:



As is quite clear, PF often encircles the high contrast transitions, and it occurs both in OOF and in fous areas, and it occurs from the centre to the extreme corner.



LoCa, Spherochromatism, or longitudinal aberrations:



85L FF LoCa from this site. BTW, in the 85L II FF test you can also see PF in the bokeh picture around the nose of the statue, which is in focus, around the highlights in the Christmas decorations (?) towards the bottom (OOF), and also around the eye and eye brow of the statue (OOF). Here is that picture, which also shows LoCa of course:



And here is a detail of the statue, which shows PF more clearly:



Note that because the nose is sharp, this cannot be bokeh fringing, LoCa, or whatever you want to call it, but only PF.



Lateral chromatic aberrations, also from this site:



The inside blue and outside yellow aberrations are clearly visible. This is from a Nikon lens, but I can't remember which one.



Another good example, but with quite different colours, is this:



From the Tokina 11-16 review here on Photozone. You can see that dark blue to purplish blue alternates with green, depending on whether it occurs on the outside or inside edge, relative to the centre of the image.



In short, just based on colour one can't decide which aberration we are dealing with, one also has to examine the actual characteristics.



For proper PF it still stands that it has a non-spherical component, and that it occurs all over the picture, and may encircle high contrast transitions completely in a single colour, single fringe, which makes for the big difference with proper chromatic aberrations, be it lateral or longitudinal.



HTH, kind regards, Wim

[wim]

[quote name='Brightcolours' timestamp='1291470806' post='4755']

If different colours have different focus planes, it may well be that AF systems are made to be more receptive to green in order to get the best results for us, the viewers of the results. Of course, black and white are not colours of light, so the same applies.



PF and LoCA are NOT the same thing. LoCA is green and magenta.

PF is purple to blue-ish (usually, it can also appear towards red oddly enough).

Nice PF example from the Sony 16mm f2.8 fisheye:



[/quote]

This is actually LA, maybe enhanced a little by PF due to the extremely high contrast transitions, but definitely lateral colour aberrations: green on one edge, purple and blue on the opposite edge.

PF in lovely "orbs":

Yep, PF

PF like we know it from compact digitals:

Nope, lateral colour aberrations again. Check the green fringing on the opposite edges to the blue ones.

Longitudinal Chromatic Aberration:



LoCA from Canon EF 100mm f2.8mm macro:





Photosites do not "react" to eachother,

Actually, they do, from an electronic POV. The charge in one may affect the charge or relative charge in the surrounding ones. This is why there was a black pixel phenomenon, f.e., early on with the 5D II.

LoCA is lens dependent. PF is lens dependent too, and seen mostly with cheaper compact digital cameras. Manufacturers have made changes in back element coating to combat PF, Sigma has introduced the DG(DC) line and Tazmron the Di(Di II) line specifically for PF (not LoCa). Nowadays you do not see PF very often anymore.

You still see it a lot. IMO it is not only lens dependent, but also sensor assembly dependent. I reckon that reflections internally to the filter assembly on top of the sensor, which as we all know in effect is a half-mirror, may also contribute to fringing effects. AFAIK, even the AA-filter itself may contribute to these effects.

You do see a lot of LoCA still, specifically with wide aperture lenses and macro lenses.

Not that often with macro lenses. Normally, lenses with relatively long tubes and smaller apertures show virtually no LoCa. There are exceptions, of course, but from my experience macro lenses have relatively few problems with LoCa.

LaCA ("normal" CA) is mostly seen with standard zooms and wide lenses, but also with other lenses. Some brands show laCA more (often) than others (Nikon, Tokina, Pentax come to mind).

Don't forget Sigma, especially their wides. The 12-24 EX is a prime example for LA (of the blue-green variety).



Kind regards, Wim



P.S.: Could not quote all of your images, unfortunately. The reply editor didn't let me.