I have some old m42 prime lens like Pentacon Multi-Coated f/2.8 135mm, and modern lens Canon EF-S 18-55 mm and Sigma 70-300 mm.
How much is the difference in the multi-coatings of old and modern lens? Some old lens are known for their Bokeh. Can difference in multi-coatings affects the sharpness, Bokeh and anything else? Can it affects the IQ when filters (circular polarizer, UV etc) are used with old lens?
Thank you in advance!
Pentax patented "Super-Multi Coating" in 1971 while still making M42 lenses. This coating is still in use today and I'm not aware of anything actually doing much better with the exception of another Pentax coating. Which means, to answer your first question: there's no difference. :)
Bojidar Dimitrov has a a very good writeup on the Pentax SMC and what it means. In a nutshell, there is some, very small, amount of light loss but you also reduce flare and ghosting in the process. That's a trade-off considered sufficiently good enough to ensure that any high-end lens has got something like this, regardless of the maker.
