This is a special version Carl Zeiss Planar 85mm f/1.4, made with with special coatings for infrared light.
F / EF / M42
2010 - 2014
f/1.4 - 16
This "Prototype" IR lens appears almost the same as the standard ZF Planar lens (non-IR version). The only aspect distinguishing it is the blue coating and "ZF-IR" stamped on the front. The production IR lens, which stated: "For Industrial Use" on the box, came with locking screws for the focus and aperture rings (like the ZF-I "industrial" lenses).
These ZF-IR range (25, 50 & 85mm) are referred to as a "unicorn" lenses, in that you're extremely unlikely to ever see one. This prototype version would make that seem common, as it would not have been intended that they left the factory. I didn't even know that it was a prototype until it turned up... when asked about it, the seller told me that he'd acquired it in a bankruptcy from an a close acquaintance.
As far as I know both production and prototype versions are optically the same.
Here is a graph to show how infrared light transmission of the ZF-IR compared to the standard ZF lens. This will provide higher shutter speeds and/or lower ISO for IR photographers, but more importantly low, or zero, hotspot. I assume that this reduces hotspot by allowing IR transmission in both directions. Letting any stray IR light to go back out the way it came in, rather than being reflected back. The blue coating is also on the rear, which could suggest this.
A fast lens producing so little hotspot is pretty amazing, but with this level of sharpness & contrast on top it's nothing short of spectacular! I was initially skeptical that Zeiss's IR coatings could make such a difference, but this lens is solid evidence that they do. Since a coating change is the only difference from the standard lens - Hotspot performance is the only benefit. There's no correction for IR focus, thus colour IR (like 590nm) remains ghosted in the corners.
I had to try this lens for portraits given it's specification. One of my colleagues was gracious enough to pose for a few snaps during a break (many thanks Jennifer!).
The first two portraits and the image of the crow are single images, but the rest are panoramas (stitched from multiple frames). This is just something that I enjoy doing to achieve a wider result with a shallow depth of field. This is another reason why I like this lens so much.