Extension tubes and focus distance

[woollyback]

Hello folks,

Just got a set of kenko extension tubes (thanks Scott) and they are great.

Can anyone tell me how to assess closest and furthest focus distance for a given lens or is it just trial and error. I have tried them on the 50mm and want to have a go with the 300 or 100-400.

Any ideas will be great

Cheers

Rob

 

[arclight]

I believe there is a mathematecal formula that uses:-
M: Magnification
a: lens-to-subject distance
b: lens-to-film/sensor distance
f: focal length

Trial and error has to be easier.

 

[C&C]

I'd go for the trial and error also, but there was a thread on this on POTN which went into the maths involved.

 

[jgs001]

Rob, my money is on trial and error... it's going to be quicker than working out the math, once the formula has been located.