Recently I came across a few Nikon MM variable iris objectives in China recently that I had never seen before. These look exactly like a normal 10x-A but with an iris section with a locking aperture control ring marked with NA (numerical aperture). This units are being advertised for $150-$300 USD each in China so expect these to sell for $600-900 USD when they appear eBay if they aren’t there already. Photo credit is almost impossible to say who owns the image, one seller is 店铺： 达实工控 (Store: Dashi Industrial Control )
The top section is some kind of mount adapter installed over the MM thread mount.
My guess was correct and they are selling on eBay USA and for more than I expected, $700 and $1595. These two sellers “borrowed” the photos and description from the Chinese seller’s site. That’s a nice profit if they can get the $1600. The asking price in China is ¥1145 yuan or about $159 USD. If you are thinking about trying to order one from China message me so I can talk you out of it. It’s not worth it, I know from multiple bad experiences.
The Nikon 10x MM objective: https://www.closeuphotography.com/10x-lens-test
More info on the Nikon 10X MM objective: https://www.closeuphotography.com/nikon-10x-measuring-microscope-objective
More on MM objectives: https://www.nikon.com/products/industrial-metrology/lineup/measuring_instruments/measuring_microscope/accessory/