Chromatic Aberrations ~ software intervention and a Sigma 24mm f/3.5 i-Contemporary

It was rather surprising to me that my Sigma 24mm f/3.5 i-Contemporary lens shows as much chromatic aberration as it does.

 

If I believed the Marketing Wizards I would've thought computer optimized optical design (such as what I was led to believe is used in current auto-focus lens design) would've been a vast improvement over earlier hand calculations (such as what was generally used to guide manual focus lens design).  Clearly this is not always the case.  There is something more going on.

 

Image processing software comes with lens correction profiles.  They correct for geometric distortion, vignetting, and chromatic aberration.  So I thought I'd have a look at how .lcp files modify the character of a currently manufactured lens.

 

I'm not sure if users can select individual corrections in RentWare products.  I imagine that people don't know nor care about the underlying automation.  In the case of RawTherapee, I _can_ select the corrections I want and I use this ability for this comparison.

 

Setup ~

• Sony A6300 set on a tripod
• +1EV (because of the strong white back-light)
• 2 second self timer, ISO100
• focusing on the stick
• Processed in RawTherapee 
  

Voila! a mundane scene of my Rescue Orchid - 

 

 

In RawTherapee I took three processing steps and share the results in the following image.

• Demosaic and color management only as the starting point
• Add chromatic aberration correction to the starting point
• Add Capture Sharpen to chromatic aberration, demosaic, and color managed image

 

 

Comments ~

 

The effects of software intervention on image processing should be rather obvious.  My Sigma 24mm f/3.5 i-Contemporary lens goes from showing a lot of chromatic aberration to becoming a sharper looking image at the first step of software chromatic aberration control. Then adding Capture Sharpen and the image takes another leap in perceived "sharpness."  After applying just these two software tools the lens behaves very well.

 

Which raises another question: Are there any tools a person can use when shooting with old lenses?  Can software correct chromatic aberrations in old lenses that do not have lens correction profiles?  I will try to answer this in the next blog post.