Guess it's all in the title.
Yashica seems to have these commonly. But I am thinking about the Canon ql17 or the Olympus 35rc.
I know it had been asked before about the quality of these adapters, but had anyone had experience with them?
I think putting all additional glass in front of lens has built in limitations, perhaps the reason Canon and Minolta never put one on the market. Likely the best was the converters made by Kowa for their fixed lens SLRs.
I have tested several wide converters on my auto-collimator and with film. Most converters only have two glass elements, and are soft. A few are better, having more elements, and the ones I've tried with good results are Fujica (for their rangefinders made around 1960), Sony HG 0737, and a Tiffen which I believe is 0.75x. The "HG" in the Sony stands for "High Grade". You will need to use ingenuity to make your own adapter for these.