多谢HOGO帮忙，拿了一套微距片，实际放大也不多，不过质量保证就是了。3片一起用还差一点点达不到1：1（可以自动对焦的），不用时是1：2的微距头。严重推荐这个头，一头多用。这个头的螺纹(Filter Threads)是金属的，其它几个50头（1.2，1.4，1.8）都是塑料的。失真也最小，看下面LINK。
[zt] from
http://www.kenrockwell.com/canon/lenses/50mm-macro.htm
Recommendations
The Canon 50mm f/2.5 Compact-Macro is a superb choice as an all-around 50mm lens. it is the sharpest and the least distorting of any Canon 50mm lens.
It may not be expensive, but this is Canon's best 50mm lens optically.
Table f/2.5 Macro f/1.8 II f/1.4 USM f/1.2 L
Filter Threads 52mm, Metal 52mm, plastic 58mm, plastic 72mm, plastic
Optics 9/8 6/5 7/6 8/6
Optical tricks Floating elements Aspherical
Close focus 0.75' (0.23m) 1.5' (0.45m) 1.5' (0.45m) 1.5' (0.45m)
Distortion +0.1 +1.5 +1.4
Instant MF override? No No Yes Yes
Weight 9.5oz/269g 4.6oz/130g 9.5oz/268g 20.9oz/592g
Mount Metal Plastic Metal Metal
Price, 4/2010 $265 $100 $370 $1,500
Price, 8/2012 $280 $110 $370 $1,500