Question: Which aperture were built or used between 1987-2001?
SQL: SELECT "Aper. in" FROM "1-23851574-2" WHERE "Built/Used" = '1987-2001';

Question: How many nationalities/sponsors for mirror/type Schmidt UV?
SQL: SELECT COUNT("Nationality/Sponsors") FROM "1-23851574-2" WHERE "Mirror/type" = 'Schmidt UV';

Question: Which telescopes were sponsored by or originated in Belgium?
SQL: SELECT "Name" FROM "1-23851574-2" WHERE "Nationality/Sponsors" = 'Belgium';