Nikon Micro-Nikkor 55mm f/3.5 pre-Ai ~ Lens Turbo II APS-C vs Full Frame

Working with various Nikon lenses to see if I can't answer the question of which lenses when used in conjunction with a Lens Turbo II focal length reducer exhibit unacceptable field curvature, here is a look at an old Nikon Micro-Nikkor 55mm f/3.5 pre-Ai lens.

 

 

Said tale to tell, when I was walking over to the port de plaisance in Saint Laurent du Var one early morning to take photographs of old cars, the Sony A6000 with this Micro-Nikkor slipped off my shoulder and hit the concrete sidewalk.  The camera took the brunt of the fall.  I couldn't believe it and didn't even feel the camera slipping down my arm.

Fortunately the camera only fell hard a foot or two.  One of the dials is a bit dodgy, now.  But other than a few dings on the camera, and one small chip on the focusing ring of the lens, there doesn't seem to have been much damage.  Both remain usable.

I bring this up in the event that the lens is now out of alignment.  I don't think it is as all my images remain clear and sharp across the field.  What's certain is that it's no longer absolutely pristine as it was before the accident.  *sniff*

Setup - 

• Sony A7 with straight-thru adapter - ISO100, 2 second timer, in-camera levels used to square the whole plot up
• Sony A6000 with Lens Turbo II focal reducer - ISO100, 2 second timer
  
• Manfrotto tripod - it's capable of securing an 8x10inch view camera, so it's sturdy enough for this
  
• Nikon Micro-Nikkor 55mm f/3.5 pre-Ai - shot at two f-stops - f/3.5 and f/8
• Rawtherapee RAW to jpg conversion - Auto-Match function (no "Capture Sharpen")
  

 

Comparison - 

Here is the scene setup.  As you can see, I moved away from using the apartment scrims (curtains) to shooting a copy of le Canard Enchaine' tapped to a flat wall.  I'm looking more carefully at field flatness, right?  Even given the all-too-often shoddy work standards around Paris, this wall is sufficiently flat for my purposes.

 

 

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

 

Comments - 

The Nikon Micro-Nikkor 55mm f/3.5 pre-Ai is sharp in the center wide open and at f/8 on both the A6000 APS-C with Lens Turbo II and the Sony A7 full frame cameras.

Looking at the extreme lower left corner of the scene at f/3.5 we see the edges are slightly out of focus.  It looks like they are equally soft between the Lens Turbo II APS-C image an the A7 full frame with straight through adapter.  

As with other lenses I've used in this way, the A6000 with Lens Turbo II corners at f/8 don't fully "clean up".  On the other hand, Sony A7 with straight-thru adapter f/8 images at the very corners are quite sharp, just as we would expect for the flat field macro design lens.

The Lens Turbo II induced field curvature "feels" very mild in this setup.  If I applied "Capture Sharpen" to the Lens Turbo II f/8 image it would appear to be sharper than the native Sony A7 full frame image out of the camera.