90mm Mikrotar-2 on eBay

[ray_parkhurst]

OK, major edit on this post. The 100mm and 65mm lenses I describe below are actually Mikroplanars, not Mikrotars. I do have a 90mm and a 20mm Mikrotar, and both are excellent objectives. So I am even more curious about this lens which bucks the trend of the RMS-mount Mikrotar series. Anyway, sorry for the misinformation...
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Some of you may have seen the 90/1.7 Mikrotar-2 for sale here:

https://www.ebay.com/itm/Ultra-rare-Mik ... 3854930367

I have both the 100mm and 65mm Mikrotars, as well as the 150mm Korrectar from the same series. I don't have a 40mm, though have been interested in a while in getting one. Indeed if anyone on the forum has one, some comments about its performance would be appreciated, and perhaps save me from buying. Performance-wise, the 100mm is quite a nice lens and has consistently done well in my shootouts. I've never tested it near its rated magnification but once I get my SnS system together I plan to do this. On the other hand, the 65mm shows quite a bit of LoCA, and although it's reasonably sharp, it's inferior to many other, cheaper solutions.

I have no idea how good the 90/1.7 Mikrotar-2 is, having only heard of its existence when this auction popped up. Again, if anyone has input, it would be appreciated.

My reason for posting is that I wanted to offer my thoughts on the optimum mag range for the 90/1.7. The other Mikrotars have an optimum mag or mag range, but lacking documentation I don't know the optimum for the 90/1.7. However, there is a potential clue in the photos...the aperture ring appears to be graduated by NA. The largest number shown is 0.1, then 0.08, and so on, so I am assuming the lens has NA of 0.1 wide open. Correlating this to f1.7 then implies that the lens is designed for m=0.5x magnification. Is this a reasonable assumption?