I was doing some photography reading on extension tubes and I came across this one that I couldn't figure out. The whole concept is a bit confusing. Any help is appreciated! 
Your 35 cm camera has a 50 mm focal length lens, also three extension tubes allowing the lens to be extended 25 mm, 50 mm, or 75 mm forward from its normal position. tubes can be used singly, in pairs, or all together. which tube(s) would you use for:
(a) copying a colour transparency, same size?
(b) making a 1 cm diameter image of a 2 cm diameter coin?
(c) making a 2 x 2 cm image of a 1 cm sq area of the coin?
Thanks!
Your 35 cm camera has a 50 mm focal length lens, also three extension tubes allowing the lens to be extended 25 mm, 50 mm, or 75 mm forward from its normal position. tubes can be used singly, in pairs, or all together. which tube(s) would you use for:
(a) copying a colour transparency, same size?
(b) making a 1 cm diameter image of a 2 cm diameter coin?
(c) making a 2 x 2 cm image of a 1 cm sq area of the coin?
Thanks!