Which size tube for 1:1 Macro?

[AndyWest]

I have a selection of MF lenses and have a set of 3 M42 extension tubes. How do i know when i have reached 1:1 magnification on a given lens? Is there a formula? It doesn't need to be 100% accurate!

My extension tubes are 6mm, 19mm & 26mm plus they can be stacked.

Thanks

 

[Dave in Wales]

Withdrawn

 

[AndyWest]

D'oh! yes of coarse! Silly me! :nuts:

Thanks

 

[vaizki]

To be more precise, the tubes give ADDITIONAL magnification of extension divided by focal length. So the total magnification depends on the original maximum magnification, tube length and focal length.

Many MF macro lenses were 1:2 or 0.5x max magnification, and to get to 1:1 you need 0.5x more. Which means 25mm extension for 50mm lens or 50mm extension for 100mm lens.