Why I argue in all length about this topic is because the Zeiss production process is almost unknown today. I could not find any description about it. Even this sample card only sheds a little light on it and leaves more questions than answers. But why does it matter? Because it might answer some strange effects that can be seen with the finished lenses.
As a collector or photograph picking one Sonnar lens in 90% of all cases is safe if you stay away from the war time and post war CZJ ones. But even then there is a chance that your Sonnar lens is not what it seems. More than once I picked a Sonnar lens by its design and then found out that it is out-of-time when checking the serial number. An out-of-time lens is one that did not match the other lenses in its serial number batch. Some Opton-Zeiss examples:
- 1.016.943, name ring = Carl ZeissSonnar 1:1,5 f=50mm Nr, filter rim=black,
- ZO batch=1953, 6700 copies
- batch name ring=Zeiss-Opton Sonnar 1:1,5 f=50mm T Nr
- batch filter rim=black
- 851.917, name ring = Zeiss-Opton Sonnar 1:1,5 f=50mm T Nr, filter rim=silver
- ZO batch= unknown
- batch name ring = Zeiss-Opton Sonnar 1:1,5 f=50mm T Nr
- batch filter rim=black
Those are authentic Zeiss lenses and nobody cheated here. But the first one uses a design that was later introduced and the second example used a design that was not in production at the time. You can not tell the difference of other valid Sonnar lenses. But looking at the serial number it can be seen that this lens should was probably build to another time but got a new name ring with the serial number of another batch.
My interpretation of this out-of-time lenses is that some lenses where send back to the production to fix them. If the damage was to severe than the whole lens was replaced with a current one with the old serial number (case 1). For others they might reuse the housing and only replaced the glass elements and put the serial number of the current donator lens on the repaired lens (case 2). This might be more or less a problem with Opton lenses as this can mainly found in their production runs.
Another issue found with Opton-Zeiss is that some design changes where not introduced with clear borders. When they changed the number of aperture blades from 12 to 11 for their Sonnar 50mm F/1.5 they did this with painting the filter rim black (before silver). Unfortunately some silver rim lenses ended up with 11 aperture blades and some black ones with 12 aperture blades. So better check before buying one if the number of blades match the design (if you care). This shows me that at that time they used the parts for old and new design in parallel.
Most of the design changes from CZJ where clean (as far as I can tell). So maybe they used a different approach to fit the parts to the glass. There are some creeping changes with the nickel Sonnars with black painted ring though. It seems they started adding chrome finish to parts of the lens or the body so in the end some aperture rings where chrome or the lens body that was previously nickeled.
My feeling when looking at the Fertig. dates from Mr. Thieles Nummernbuch is that producing a lens took a long time. At the beginning 100 lenses maybe needed one month but later 500. Unfortunately the sample card does not give answer to the question how long does it take to grind the glass, produce all the parts of the lens and assemble it. It does not answer the question if design changes could appear within a production batch and if those changes where applied accurately. Looking at the finished lenses I can tell you that design changes where made within batches too.
