This Carl Zeiss Jena Sonnar 5cm F1.5 is a bit of a mystery. Bought off of Ebay, SN190xxxx block. It arrived with a lot of oil on the blades, internal haze, no signs of ever being opened. The namering of these Sonnars is held in place with black paint on the filter threads, usually makes getting the ring off fairly difficult. It’s easy to tell when one has been worked on- marks in the paint and on the namering. My lightweight spanner was no match for the paint, and out came the heavy duty spanner- got the ring off with a lot of resistance. Same with the front triplet, retaining ring firmly in place. Cleaned the glass and realized all of the surfaces were coated. Some light cleaning marks on the front element and rear surface, but nothing bad. All the haze cleaned off, flood cleaned the blades, took the aperture ring off to get out the original grease. This was running, and is the source of oil on the blades. Relubed with a little vacuum pump grease.
Tested the lens on the Olympus EP2 using a contax to M-Mount, and M-Mount to u-43.
At F1.5:

100% crop:

FOR COMPARISON, an Uncoated SN207xxxxx lens with near perfect glass, also CLA’d.


Back to the Coated lens:
At F1.5:

100% crop:

At F4:

100% crop

The earliest Sonnar "T" that I have is a SN255xxxx block. This one is a surprise, bit of a mystery. I have a Sonnar that was coated after manufacture, and it is easy to find the signs that it had been disassembled, coated, and put back together. This lens shows no signs of ever being worked on. Zeiss started coating lenses in the mid 1930s, this lens has a serial number that dates it to 1936.
"Could Be" one of the earliest of the coated Sonnars.
Tested the lens on the Olympus EP2 using a contax to M-Mount, and M-Mount to u-43.
At F1.5:

100% crop:

FOR COMPARISON, an Uncoated SN207xxxxx lens with near perfect glass, also CLA’d.


Back to the Coated lens:
At F1.5:

100% crop:

At F4:

100% crop

The earliest Sonnar "T" that I have is a SN255xxxx block. This one is a surprise, bit of a mystery. I have a Sonnar that was coated after manufacture, and it is easy to find the signs that it had been disassembled, coated, and put back together. This lens shows no signs of ever being worked on. Zeiss started coating lenses in the mid 1930s, this lens has a serial number that dates it to 1936.
"Could Be" one of the earliest of the coated Sonnars.