Correction of CA before the digital world?

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b_gossweiler

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As far as I understand it, CA is caused purely by lens inperfection. Today, everybody thinks that correction of CA is a must in processing an image.

I just wonder now, how was CA corrected before images were processed digitally? Or was it not at all?

Beat
 
I am assuming that CA stands for Chromatic aberration. I am not aware of any way of correcting chromatic aberration before the digital world. the only way to prevent that is buying a better lens. I remember my first telescope- tasco refractor- what a piece of junk. By looking into that telescope, you would see chromatic aberration at its finest.

Bob- the slide shooter at heart
 
Not at all sure about this, but isn't the answer that light hits film molecules in a less-uniform way than it hits a pixel on a sensor array?

John
 
[quote author=johnbeardy link=topic=97'1.msg65647#msg65647 date=1272524'36]
Not at all sure about this, but isn't the answer that light hits film molecules in a less-uniform way than it hits a pixel on a sensor array?

John
[/quote]Film "Grain" was not a uniform distribution. But I do not think this has anything to do with CA or correcting it. CA and distortion are properties associated with poor quality lenses. Now that we can have a digital process to correct this, I am financially in a position that I don't have to buy cheap lenses. I can say that I have never used the CA Correction in LR or have I needed to. Even though most of my lenses are Pentax, and while they may not be entirely free of CA, It is thankfully so small as to be ignored. Perhaps I should process some of my P&S camera photos with LR. Those cameras with Lucite lenses should exhibit CA worthy of correction.
 
My 18-2'' lens needs CA correction when its at 18mm but most of my other lenses are pretty good. Harsh lighting / contrast can cause it even in expensive lenses. The CA correction in LR is very good, I was not so happy with the Aperture 3 CA tools but the latest 3.'.3 release has supposed to have fixed it.
 
I have heard several times that CA Is more strongly visible on sensors than film, especially the dense sensors of non-FX cameras.

It certainly seems true, at least I have an old Nikon 2''mm lense from the 7''s that was "good" back then, but is horrible for CA now. Don't think the lens changed.

Is it true?
 
I'm certainly no authority, but my quick and dirty research indicates that CA was a lesser problem with film, transparency and paper, than with digital sensors, as Linwood say.

I presume there were specific exceptions. I'd expect astro, or other ultra high contrast genres presented special problems. Denis P., Bennett?
 
Yes Brad. It was (is) a problem with astro-imaging. You can minimise by using a reflecting telescope rather than a refracting telescope but still... It is mostly noticeable with the Moon or bright planets like Venus but on everything with poor optics. This is why we prefer to take shots at each wanted wavelength with their own focus and combine thereafter to make a true (or false) color image.

Nik. Note that Adobe Labs just released their Adobe Lens Profile Creator that can take CA in account.
 
Thanks for your responses, helps me understand a little more about the subject.

Beat
 
As a step further, some systems like my Panasonics, do the CA correction in camera,

Dave
 
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