06-15-2011, 11:43 PM
(This post was last modified: 06-15-2011, 11:59 PM by Brightcolours.)
[quote name='wim' timestamp='1308178761' post='9270']
If you mean less desaturation in the centre and more towards the edges: that is what I mean by selective desaturation.
Well, let's just agree to disagree in that case. What [color="#ff0000"]you[/color] see is PF and some LoCa, what[color="#ff0000"] I[/color] see is PF, LoCa, and lateral CA. IOW, WE do not see the same things, IOW, don't use WE in this case unless you are of royal descent and head of state. I am not in the group with the same opinion here, so please don't say "we".
As I mentioned: not with Nikkor lenses, and as I mentioned, it was defined with yellow and blue; I was taught so about 35 years ago that CA was defined as yellow/blue artefacts.
Regards, Wim
P.S.: I am out of here, I don't have time for these discussions. As mentioned, I only wanted to add some hopefully useful info to this topic. You don't agree with me, but I didn't really expect anything else.
Cheerio.
[/quote]
Stop talking about desaturation, I have not mentioned desaturation.
You SHRINK the size of the offending channel. Lets say, red is projected slightly bigger. The red channel then needs to be shrunk, in order to match green and blue again. So.. while keeping the CENTER of the image in place, we shrink the image. Literally: The image may be 4000 pixels wide, and we might shrink the red channel to 3997 pixels, if that would be the amount needed to map red on the other information correctly again.
That is how one corrects LaCA. Some software does it that way, like Photoshop in its lens correction functionality, or DDP. Or you can do it by hand in PS too.
Some software or in-camera firmware does not correct CA, but masks it by desaturating coloured edges.
And yes, we do see the same thing, you just do not know what LaCA actually shows up as, so you label what you see wrong. Still it is the same thing we see, you and I.. PF.
Whoever taught you 35 years ago that CA was blue and yellow artifacts, taught you wrong. No biggie, as we are never too old to learn. For fun, I looked up "chromatische aberratie" in my "het objectiven boek" (the lens book) by Rudolf Smit, printed in MCMLXXIII, so 1973.
It mentions that blue gets bent ("gebroken") most in comparison to red, and from then on he just talks about red and blue edges around the contours of the image projected by the optics. Nothing about Nikon, nothing about yellow and blue artifacts being the definition of CA (LaCA), Nothing linking Nikon specifically to the definition of CA.
So, that was the state of art of explaining CA 35 years ago, and Rudolf Smit was teacher of photography at the "Amersfoortse Academie", did the test reports for the Dutch Foto magazin "Foto" and "Focus", if I am not mistaken.
On a side note, I have Nikon lenses from the 60's and 70's (ultra micro Nikkor 28mm f1.8, ultra micro Nikkor 55mm f2, original Nikkor 55mm f3.5 micro, Nikkor 35mm f2.8, Nikkor 50mm f2, Nikkor 85mm f1.8, Nikkor 135mm f3.5) and I have not noted a tendency to blue/yellow CA specifically, with them. Also looking at older designs being tested online, I tend to find red/green-blue CA (35mm f2, 24mm f2.8). 50mm f1.8 shows blue/yellow.
I know that whenever something you say gets corrected, you react this way. You do have the time for discussions, you just hate when someone disagrees with a part of what you wrote, or corrects part of what you typed up.
I do wish we could have normal discussions.
Anyway, sorry but what you labeled as LaCA simply is no LaCA at all. It shows no signs of being that in any way (lacks the directionality of LaCA, lacks the complementary colours, lacks the width and character of the coloured edges).
As such, it was not useful info.
If you mean less desaturation in the centre and more towards the edges: that is what I mean by selective desaturation.
Well, let's just agree to disagree in that case. What [color="#ff0000"]you[/color] see is PF and some LoCa, what[color="#ff0000"] I[/color] see is PF, LoCa, and lateral CA. IOW, WE do not see the same things, IOW, don't use WE in this case unless you are of royal descent and head of state. I am not in the group with the same opinion here, so please don't say "we".
As I mentioned: not with Nikkor lenses, and as I mentioned, it was defined with yellow and blue; I was taught so about 35 years ago that CA was defined as yellow/blue artefacts.
Regards, Wim
P.S.: I am out of here, I don't have time for these discussions. As mentioned, I only wanted to add some hopefully useful info to this topic. You don't agree with me, but I didn't really expect anything else.
Cheerio.
[/quote]
Stop talking about desaturation, I have not mentioned desaturation.
You SHRINK the size of the offending channel. Lets say, red is projected slightly bigger. The red channel then needs to be shrunk, in order to match green and blue again. So.. while keeping the CENTER of the image in place, we shrink the image. Literally: The image may be 4000 pixels wide, and we might shrink the red channel to 3997 pixels, if that would be the amount needed to map red on the other information correctly again.
That is how one corrects LaCA. Some software does it that way, like Photoshop in its lens correction functionality, or DDP. Or you can do it by hand in PS too.
Some software or in-camera firmware does not correct CA, but masks it by desaturating coloured edges.
And yes, we do see the same thing, you just do not know what LaCA actually shows up as, so you label what you see wrong. Still it is the same thing we see, you and I.. PF.
Whoever taught you 35 years ago that CA was blue and yellow artifacts, taught you wrong. No biggie, as we are never too old to learn. For fun, I looked up "chromatische aberratie" in my "het objectiven boek" (the lens book) by Rudolf Smit, printed in MCMLXXIII, so 1973.
It mentions that blue gets bent ("gebroken") most in comparison to red, and from then on he just talks about red and blue edges around the contours of the image projected by the optics. Nothing about Nikon, nothing about yellow and blue artifacts being the definition of CA (LaCA), Nothing linking Nikon specifically to the definition of CA.
So, that was the state of art of explaining CA 35 years ago, and Rudolf Smit was teacher of photography at the "Amersfoortse Academie", did the test reports for the Dutch Foto magazin "Foto" and "Focus", if I am not mistaken.
On a side note, I have Nikon lenses from the 60's and 70's (ultra micro Nikkor 28mm f1.8, ultra micro Nikkor 55mm f2, original Nikkor 55mm f3.5 micro, Nikkor 35mm f2.8, Nikkor 50mm f2, Nikkor 85mm f1.8, Nikkor 135mm f3.5) and I have not noted a tendency to blue/yellow CA specifically, with them. Also looking at older designs being tested online, I tend to find red/green-blue CA (35mm f2, 24mm f2.8). 50mm f1.8 shows blue/yellow.
I know that whenever something you say gets corrected, you react this way. You do have the time for discussions, you just hate when someone disagrees with a part of what you wrote, or corrects part of what you typed up.
I do wish we could have normal discussions.
Anyway, sorry but what you labeled as LaCA simply is no LaCA at all. It shows no signs of being that in any way (lacks the directionality of LaCA, lacks the complementary colours, lacks the width and character of the coloured edges).
As such, it was not useful info.