Blur Radius vs Blur Falloff ~ Cosina Cosinon 55mm f/2.8

The Cosina Cosinon 55mm f/2.8 is a tessar formula, first element focusing lens.  I'm trying to adapt is to miniature format soft focus work by using the first and second element separation control of the focusing ring to manage softness level.  Mated to a helicoid and setting the softness level on the focusing ring, the helicoid is used to effectuate the focus itself.

To show how first and second element separation effects softness level, I graphed Blur Radius against Blur Falloff.  Further, to control highlight "softness", I added a number of different Soft Focus filters to the investigation see to what degree they do their job. 

Here's how to read the following graphs. 

Comments ~

It should be easy to see how the focus ring on the Cosina 55mm can effect the level of softness in an image.  And it should be easy to see how Soft Focus filters add softness over the base optics.

While not shown here, but illustrated earlier, the Cosina tessar formula lens is better corrected for closer focused subjects when the lens is shot wide open.  Stopped down, infinity cleans up nicely. 

I believe this proves the concept of using first element focusing lenses on miniature formats in Soft Focus work.