# Extension tubes and mfd



## Cinto (Jan 17, 2015)

Quick question about extension tubes. When using a lens(especially one without floating elements) on extension tubes is it best to focus at infinity where the lens may be sharper and ad more extension if needed or use the mfd?
I'm going to be using the 40mm pancake I think. Thanks


----------



## Tanispyre (Jan 17, 2015)

If the lens does not have floating elements, and moves as a whole group to focus, then it makes no difference whether you focus at infinity or mfd. As the lens focuses from infinity to the mfd, the lens moves out away from the film plane, it is effectively the same thing as adding a small extension tube. Air behind the lens is the same whether it comes from changing focus or adding tubes.


----------



## ecka (Jan 17, 2015)

Infinity or not, I didn't notice much difference. 40STM pancake works great with extension tubes. I'm using Marumi Ext. Tubes 13+21+31.
13mm gives me ~ 0.33x at infinity and ~ 0.5x at MFD. Not a small magnification difference (1:3 vs 1:2).
21mm ~ 0.55x - 0.7x
31mm ~ 0.8x - 1.0x
I think that sharpness depends on the lens itself. If it's not that sharp at MFD, then it won't be with ext. tubes as well.


----------



## Cinto (Jan 18, 2015)

Thanks for the info.


----------

