Nikon Nikkor 24mm f/2.8 Ai ~ AA filter "sharpening" effects

Writing a recent entry on rediscovering the Nikon Nikkor 24mm f/2.8 Ai and the fact it actually has a flat field afterall, I stumbled on something that I'd like to consider here.

Capture Sharpening.

This is something that Lightroom and Rawtherapee provide.  It is a function that attempts to offset the effects of Anti-Aliasing filters.  AA filters are used to combat moire in digital sensors.  Canon is famous for using strong AA filters.  Sony, from what I understand, has much lighter AA filters in many of their mirrorless camera offerings, including the NEX/A6xxx and A7 products.

I've been using Rawtherapee's Capture Sharpen without really thinking about it.  My images are "sharper", so what's not to like, right?

A couple years ago I acquired a very low mileage (ie: <700 click) Sony A7 full frame light grabbing mirrorless monster.  While this is only the Mark I version of a long line of great Sony 24 mpixel cameras it really performs.  The sensor is very quiet (ie: no noise) and is far sharper than any Canon DSLR I ever used (and I used a lot of them). Do I really "need" Capture Sharpen to crisp images up???

Using images from a prior post I applied Capture Sharpen to images at two apertures to see what effect the function had on the basic off the sensor image.

Setup - 

• Sony A7 - ISO50, 2 second timer, in-camera levels used to square the whole plot up
• Manfrotto tripod - it's capable of securing an 8x10inch view camera, so it's sturdy enough for this
  
• Nikon Nikkor 24mm f/2.8 Ai - shot at f/2.8 and f/8
• Rawtherapee RAW to jpg conversion - Auto-Match function plus Capture Sharpen

Comparison - 

Here is the scene setup.  It's just a pair of closed gaze scrims in our apartment.

 

 

[As always, click on the image and look at it to 100percent file size to see whatever there is to be seen.]

 

 

Comments - 

Looking at the images at f/2.8 we can see where Capture Sharpen function lives up to its name.  Capture Sharpen'd images at f/2.8 are "sharper" looking that images out of the camera at f/8.  And at f/8, Capture Sharpen takes images yet another step further into "sharp."

I am "good" with all this, until I start looking at the contrast in the out of focus regions (that little peek between the scrims).  It's there that something interesting is taking place.  The "soft smoothness" of the out of focus rendition is starting, to my eyes, become a little harsh.  The light/dark transitions have become rather "steep" and "contrasty."

Now I'm confronted with a reality of software processing "enhancements."  I ask myself several things - 

• Is this really how I want my images to appear?
• Does software intervention go some ways toward eliminating optical effects?
• What if native lens rendering, defects and all, are what attracted me to a set of lenses in the first place, only to be removed by software?

That last question is something rather interesting.  

For instance, let's say a lens manufacturer like, oh, let's take Nikon as an example, _deliberately_ designed their old manual focus lenses to be soft wide open and sharpen up as the aperture is stopped down.  

Let's say Nikon knew their Japanese customers _loved_ soft rendering under certain circumstances to create a "delicate" look.  

Let's say Western customers know little to nothing about any of this and just want "sharp", "sharp, "sharp" at all costs and at _all_ apertures.  Or, let's say that modern AF systems require a certain level of resolution wide open to focus accurately.

Which leads me to a related conversation made some years ago around the photo-forums.  That was the subject of "focus shift" between wide open and stopped down.  In particular, I remember comments about Nikon Nikkor 50mm f/1.4 lenses being prone to this dastardly defect.  Oh the horror.  Oh the hopelessness.  Oh the hand wringing.

Only... if a lens is designed to be deliberately soft wide open it will give the Japanese markets desired "delicate" effect.  It will exhibit under-corrected spherical aberration behind the point of focus.  One of the things about under-corrected spherical aberration is that there is a region, not just one point!, where an image will appear to be in focus.  

The implications of this are several fold and it might take several tumblers of the "Good Stuff" to think through all this and to come to an enlightened understanding of what's really going on.  I'll comment a bit more on these things in a future post.

Coming back to the effects of Capture Sharpen on softer images shot wide-open, I see where it's possible to make such an image appear as "sharp" as anything shot at other apertures.

The questions are: Is this really what I want?  Or do I want to retain the "character" of a lens as it was originally designed?