Originally posted by MattGunn Testing with a geiger counter I found that the rear elements of the f/1.8 are radioactive and the f/2 arn't. This means that they use a different type of glass and so if their performance is similar then the optical design must be different. I havent done any serious comparisons of their performance yet though.
It is the f/2 that should be readioactive. If that is not the case, you may have a rare f/1.8. I do not doubt that it could have happened based on the sample variation I have seen.
Notwithstanding the thoriated glass, please note that the optical formulas are the same. Please refer to:
Die Cast Pro - Asahi* Optical Super-Takumar 55mm f/2.0
However, technically, since the glass **is** different, the performance may vary.
The optical properties attendant upon the use of thorium are high refractivity and low dispersion and these would tend to operate to minimize chromatic aberration. If handled properly to remove any yellowing, we might posit the notion that the f/2 is a ** superior ** lens in this respect.
I doff my hat. You have the last word.
woof!