extention tube calculations? help needed.

[hamada]

hi, i bought a set of extention tubes for my macro work.

i need someone who can to explain to me how to calulate the new MFD and magnification.

for example when i put a 25mm extention tube on my 90mm macro that has 29cm MFD and 1:1 magnification... what is the new MFD and magnification?

or what if i put a 31mm extention tube on my 70-200mm f4.

is there maybe a good website that explains how to calculate this?

[J.R.]

Try this ...

http://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm

[TW]

Simply divide the amount of extension by the focal length pf the lens. 25mm ext/ 50mm lens = 1/2x, or 50% magnification. Also, just take a pic of a ruler and do the math!

[Canon-F1]

Also, just take a pic of a ruler and do the math!

yeah why not invent the wheel again.   

sure much easier to do that for a dozend lenses * 3 extention tubes then searching a formular. 

http://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm

+1

was going to post that.