28 mm ml or dx

Hello bluedxca93 and welcome to the Forum! It might help to unpack and separate a couple of things in order to answer the questions you have.

I'll assume that by "purple fringing", you mean CA, or Chromatic Aberration, and that's not tied to any negative effects solved by either of the common types of coatings - HR (older, High Reflectant) or AR (newer, Anti-Reflective) - or even for uncoated lenses. CA occurs when there's an inconsistency in the alignment of light rays of individual color spectrum ranges as they converge on and hit the focal plane.

Typical case of CA... this shows the results from a Yashica Yashikor 135mm f/2.8 in M42 mount on a Sony A7R full-frame, paired with the corrected results in Lightroom v5.6.



CA is introduced to some degree by the optical design, as a combination of glass types and the layout of elements and groups of the individual/cemented lenses. It is corrected 'in-lens', by using advanced designs and better glass formulas that are specifically designed to minimise or eliminate the problem. Generally, that means additional expenses for lens makers, and those are often found in the higher priced non-budget lines offered by the brand. Unfortunately it can also be prohibitively expensive on some focal lengths under certain designs, but it's usually better controlled when there is a premier line (or two) above the generic/base line.

It's likely that there are cases I'll miss something, but basically each mount type sold by Yashica (and most other OEM's of the same periods) had at least two levels of quality over the years. The higher the level, the better overall build and optical quality, and the higher levels benefitted with better designs and better - or multiple - coatings. In M42, Yashica had at least three lines with different coatings... DS (single HR, or none), DX (single/double HR), DS-M (early AR), and in C/Y there were even more, in both HR and AR coatings, or none at all... ML (AR), MC (HR and AR), DSB (HR or none), and YUS (usually, none).

Generally, the newer a lens is, the better it's likely to be -BUT- there will be exceptions. Thorium was used in some focal lengths, in some lines (radioactive elements), which affected the transmitted optical properties, and cost-cutting strategies could lower the optical quality too much (i.e., Yashica MC Zooms). In short, a DS or DX lens can produce inferior results compared to the later ML version.

Another 'correction' has to do with the aperture. A wide open lens is far more likely to exhibit major CA issues, than the exact same lens will when it's closed down by one full stop. There will be cases where 1 1/2 stops can eliminate CA completely. Personally, I rarely ever shoot any wide-angle lens anywhere close to wide open, and specifically, I never have a single CA issue with any ML 28mm I own... and my guess would be that I'd have 5+ of both the original chrome-edged diamond-gripped early models, and the later all-black rectangular grip versions.

It's certainly possible that any production run might have a few with reversed or faulty elements, or were badly assembled. There are particular models that are known to have wide swings in sample quality, but I don't recall anything specifically about the 28mm of any series.

If I have a 28mm DX or even their spec sheets, they'd be in storage... but count the additional colors in the reflections. If you see a second one with a yellow tint, and a third that's pink/peach, then it's likely double coated. One Yellow-ish and a regular 'untinted' reflection -or- all yellow-ish, would likely be a single.