CZJ 50mm f2.0 Sonnar T yellowing

[jwnash1]

I received a CZJ 50mm f2.0 Sonnar T in Contax mount today. The coating gives a faint blue reflection on the glass but when you look through the lens at a sheet of bright white paper the paper takes on slight yellowish tinge. The effect is almost identical to that seen in the radioactive glass of the f1.4 50mm Super Takumar, although maybe not quite as strong. The 3500000 serial number places the manufacture date somewhere in the 1953-54 era. Is this normal for this lens or is there something wrong with it?
John

 

[Sonnar Brian]

I suspect it is the Balsam that is yellowing, I do not believe Zeiss used Thorium Glass in it. Old Balsam yellows, but not anywhere near as much as Thorium Glass. The latter gets almost like a Light Yellow filter for B&W.

Try some color pictures with it.

 

[jwnash1]

Yeah Brian, the Light Yellow filter is a pretty good description. I will run some color film and see how it comes out. Actually, I probably will use it for B&W a lot so it will not be an issue. I was curious though because I had never heard of the yellowing on Zeiss glass where as being a long time screwmount Pentax user I have cured several lenses with sunlight. The balsam certainly makes sense.