GREAT information here.
I'll have to look at mine.
I bought two last year, #I, and # II, 72mm, I believe mine were Contax.
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Until a few years ago I used two Nikon filters (different strengths). They seemed to me to produce a very nice effect though I never owned a dedicated soft focus lens so I have no basis for comparison. Someone whose opinion I respected told me that the Softar and Nikon soft focus filters were the best then available. Today I don't use soft focus filters, I use Photoshop, which I prefer because it allows me to produce the exact effect I want without being locked in (more or less) to what's on the negative.
Thank you all very much. I now have a much better understanding. I will look for the Softar filters, but also for a SF lens. Seems that even great filters still are not an easy replacement for a SF lens. Thank you again for your great and detailed feedback, it is always amazing how much help I get here. I hope one day I can make it up by helping others as much.