As of 2005, there were over 50 churches recognized as cardinalatial deaconries, though there were only 30 cardinals of the order of deacons. Cardinal deacons have long enjoyed the right to "opt for the order of cardinal priests" (optazione) after they have been cardinal deacons for 10 years. They may on such elevation take a vacant "title" (a church allotted to a cardinal priest as the church in Rome with which he is associated) or their diaconal church may be temporarily elevated to a cardinal priest's "title" for that occasion. When elevated to cardinal priests, they take their precedence according to the day they were first made cardinal deacons (thus ranking above cardinal priests who were elevated to the college after them, regardless of order).

How many cardinal deacons were there in 2005?