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Extension Tude 25mm

hi there

i am currently using a Canon 800mm 5.6 on a full frame 1Dx body.  this gives me a "minimum focal distance" of 6m.

i understand that if i use an extension tube, this effectively minimizes my "minimum focal distance", but also reduces my AF range, such that i lose infinite AF ..

i have searched the net and the foumlars i have found are somewhat confusing for me .. can some one help me figure out;
a) what is the minimum focal distance with the 25mm extension tube attached?
b) what is my maximum AF range with the 25mm attached?
c) what is my minimum focal distance if stacked 25mm with 12mm?

thanks in advance .. cheers

google simple search and find the following url:

[url]http://flybacon.com/Cameras/Macro.aspx[/url]