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Guest Message by DevFuse
 

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No visible CA even in the bokeh area


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5 replies to this topic

#1 videogamemaker

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Posted 15 March 2011 - 04:46 AM

It was my understanding (but not sure why I think this is true) that CA can be corrected along the edges of sharp objects, but not fully for the out of focus areas. Is this true? I always thought it was because you could figure out how many pixels worth (in a full size raw image) of CA to subtract out for the focus plane, but items out of focus exasperated the aberrations and there was no way to know just how far out of focus they were to subtract the right amount out from the blurry edges.

I ask because I noticed this from the 2nd X100 vs X1 shootout on flickr:

Posted Image

The X1 image has some CA (acceptable, but it's there) on the blurry tree in the background (on the leaf edge too, but any good software would take care of that). The X100 image has none on the leaf, which the jpeg engine could be correcting in camera, but neither does the blurry tree in the background. This points to the lens actually having a near perfect lack of CA, right? Is this a logical conclusion or am I missing something related to how lenses and CA works?

#2 brkl

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Posted 15 March 2011 - 05:20 AM

They are different kinds of CA. Lateral CA is the regular kind and can be fixed in PP. Longitudal CA colours everything beyond the focus plane slightly green and IIRC everything in front of the focus plane slightly blue. They are different phenomenona. Longitudal CA has to be fixed in the lens and it does seem like the x100 lens is good at that.

#3 videogamemaker

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Posted 15 March 2011 - 05:32 AM

They are different kinds of CA. Lateral CA is the regular kind and can be fixed in PP. Longitudal CA colours everything beyond the focus plane slightly green and IIRC everything in front of the focus plane slightly blue. They are different phenomenona. Longitudal CA has to be fixed in the lens and it does seem like the x100 lens is good at that.


Thanks for the clarification. Now I am curious if the lens is just plain awesome at having a lack of both CA or if it's corrected in lens for Longitudal, and in camera software for lateral.

#4 wchutt

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Posted 15 March 2011 - 07:14 PM

It was my understanding (but not sure why I think this is true) that CA can be corrected along the edges of sharp objects, but not fully for the out of focus areas. Is this true? I always thought it was because you could figure out how many pixels worth (in a full size raw image) of CA to subtract out for the focus plane, but items out of focus exasperated the aberrations and there was no way to know just how far out of focus they were to subtract the right amount out from the blurry edges.

I ask because I noticed this from the 2nd X100 vs X1 shootout on flickr:

Posted Image

The X1 image has some CA (acceptable, but it's there) on the blurry tree in the background (on the leaf edge too, but any good software would take care of that). The X100 image has none on the leaf, which the jpeg engine could be correcting in camera, but neither does the blurry tree in the background. This points to the lens actually having a near perfect lack of CA, right? Is this a logical conclusion or am I missing something related to how lenses and CA works?


There's yet another sort of CA that has little to do with the lens. The sensor's micro lenses can have CA of their own. Most purple fringing is a combination of sensor bloom and micro-lens CA.

Here's a reference: (scroll to the bottom of the page)

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I am willing to speculate the X100's low lateral CA and minimal level of purple fringing artifacts has to do with the micro-lens array being carefully designed to match the lens' optical characteristics.

It is possible that EXR processor firmware repairs lateral CA much like newer Nikon DSLRs and LUMIX G series micro-4/3 cameras. The few X100 RAW files I've been able to process myself with Raw Photo Processor did not exhibit lateral CA, which could mean it's the just the lens/sensor combination. We'll eventually find out.

#5 disign

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Posted 16 March 2011 - 01:39 AM

Yes, two types of chromatic aberration axial (longitudinal), and transverse (lateral).
Axial aberration is very well controlled in the x100, a true apochromatic lens design. You can not hide axial aberration with in camera software.
There is a touch of transverse aberration visible in the raw files I saw, but pretty much under control. It's not up to the level of voigtlander apo lanthars 125/180, but is very good for a modern lens. Lens engineers seem to rely more and more on software to correct aberrations. X100 is correcting perfectly these slight traces of transverse aberrations.
So regarding aberrations the lens is a stellar performer.

#6 videogamemaker

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Posted 16 March 2011 - 04:45 AM

Yes, two types of chromatic aberration axial (longitudinal), and transverse (lateral).
Axial aberration is very well controlled in the x100, a true apochromatic lens design. You can not hide axial aberration with in camera software.
There is a touch of transverse aberration visible in the raw files I saw, but pretty much under control. It's not up to the level of voigtlander apo lanthars 125/180, but is very good for a modern lens. Lens engineers seem to rely more and more on software to correct aberrations. X100 is correcting perfectly these slight traces of transverse aberrations.
So regarding aberrations the lens is a stellar performer.


Thanks to both of you for the excellent explanations. I feel much more informed now.




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