[Leica] Tale of Two Telyts Part Deax - The Evil Twin - Doug Herr's observation

[rpalmier at depaul.edu (bob palmieri)]

Doug Herr wrote:

  Prompted by this discussion and an off-list question I checked a couple
of my 560/DMR files and found color fringing adjacent to some very
bright off-center twigs/grasses etc.  The color fringing was identical
(green) on both sides of the twigs leading me to believe it's not a
chromatic aberation in the lens, rather it's where the red and blue
channels hit their limits before green did.


Doug:

Thanks for digging into this further.  Yes, since I understand lateral 
chromatic aberration to be a variation in magnification with 
wavelength, your effect is quite likely due to some sensors running out 
of headroom before others.

In fact, this also explains how a similar effect could occur with 
different film layers hitting their own limits at different light 
levels.

It also explains why the CA correction features in RAW converters don't 
fix this kind of thing, since they vary the respective magnification 
levels among the channels (I think.)

Plus, it reinforces my intuition that a lens with that much actual CA 
probably wouldn't produce such great images under conditions of normal 
exposure.

I expect that a few more bits of useful info will come to light soon, 
but for the moment I think the collective wisdom of the list leads to 
the following useful ideas:

1. Watch them edges in the blown highlight areas.

2. If you see any of this stuff, attack it with the Desaturation Brush. 
  (Once again, a great reason to feel lucky to be shooting in the Age of 
Computer-Based Corrections.)

3. As my hockey playing buddies say, "Shoot!!!!!!!!!!!!  
Shoot!!!!!!!!!!!!!!!!"

Bob Palmieri