Quote Originally Posted by Fast Glass


Additional magnification=(extension tube length)/(lens focal length)


Based on this rough rule, the extension tube mounted between the camera body and your 500mm will result in a .05x magnification gain (25mm divided by 500mm).


Hope this helps,


John.
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Thanks John, I think your getting me pretty close----But how do you apply this formula to MFD? Would this .05 increase in magnification be the same as a .05 decrease in MFD?