Is there a difference in a " Rapid Aplanat" and an "Extra Rapid Aplanat", or was that just turn of the century marketing?
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Is there a difference in a " Rapid Aplanat" and an "Extra Rapid Aplanat", or was that just turn of the century marketing?
There's even a difference between "Aplanat" and "Aplanat", depending on who made it!
but in general, an "Extra Rapid Aplanat" would be something like f:5 to f:6, while a "Rapid Aplanat" would be f:6 to f:7. Just "plain Aplanat" tends to be f:7.2 to f:7.7.
It doesn't look like much of a difference, but it was important at the time (especially in marketing). :)