RE: the original post, it would be helpful to know what is meant by "the same optical formula."
A few comments may apply. The Summarit is the same optical formula as the Schneider Xenon, as already mentioned. (Not sure if that was the question.) The Summilux was an evolutionary development of, but at f/1.4, not quite the same formula as, the Summarit. The Summarit has two thin elements at the rear, as does the first version Summilux that followed. Later, the Summilux was redesigned with a cemented doublet at the rear. Interestingly, when Walter Mandler redesigned the Noctilux so as to not require aspherical elements, one of the things he did was to return to the two thin elements at the rear.
The Summarit is of low contrast wide-open, improving to a medium contrast when closed down. It ptoduces a "classic" look, rather than tack-sharp. I used to have one, and wish I had it back.
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