Macro extension tubes - Help me with the maths

[sam_cat]

So, on a full frame body, with the Canon 100mm F2.8 macro lens (that focuses down to 1:1), if focused and 1:1 and I use 50mm of tubes, what is the size ratio?
Would 100mm of tubes on a 100mm lens give 2:1 (ie subject is twice life size on the sensor)?

And how does it work with a crop camera?

Thanks,
Sam

 

[Dogfish_magnet]

Added magnification = Extension / Focal Length

so 50 /100 = 0.5 giving a total magnification of 1.5:1 on both FF and Crop, in practice you may get more magnification as the focal length of your macro lens is probably less than 100mm at 1:1

 

[sam_cat]

Thanks for that, makes sense.



Sam