[lesliehui]

I have question on magnification index.

a) 24~70mm f/2.8L --- Max. magnification index = 0.29, Min. focus distance = 0.38m

b) 70~200mm f/2.8L --- Max. magnification index = 0.17, Min. focus distance = 1.4m

Which setup will have a bigger butterfly image on output ?

Setup one : Use len "a" to focus on a butterfly at its min. focus distance =0.38m (zoom at 70mm).

Setup two : Use len "b" to focus on the same butterfly at its min. focus distance = 1.4m (zoom at 200mm)

Is there any web site to describe or calculate the output subject size ?

[NewToCanon7D]

又或者 70mm 及 200mm zoom 盡 可以張主体拉近多遠/尺呢?
如果加 EF 1.4x ll Extender 或 ef 2x ll eXTENDOR 会把光圍減細一級及二級之外, AF 是盃變得很慢又或者出現OUTFO呢? 最後,成相有否下降及唔SHARP 呢? 謝謝各位師兄!!

[william_lau]

其實唔駛諗咁多，睇個放大率就ok. 以你個問題，假設隻蝴蝶係你幾近影都唔會飛走的話，咁24-70會影得大D。 仲有，佢話最近對焦距離，未必一定係遠攝端個喎。

[xdick]

"最近對焦距離" 好似means 任何焦段都係果個~
eg. 由24至70的最近對焦距離都是0.38m~