Hasselblad extension tubes old vs new

[Slixtiesix]

I´m about to add an extension tube to my newly acquired 180/4. Is there any reason to eschew the older (10,21,55) extension tubes?
I thought about adding the 21mm. Which tube do you think recommendable for the 180mm Sonnar?

[jeffreyg]

I believe the newer tubes if type E have electronic contacts and are 16E, 32E, and 56E. The tubes including the ones you mention can also be stacked. There is a chart which I don't have handy that will tell you the exposure compensation and other information about magnification, etc. It might be available on the Hasselblad web site or through a web search. I have a set of three above plus the 8. I think the 21 is considered useful for portrait shots. I can stack the 8 and 16 with my 150mm lens for about the same affect as a 21 with the 180.

http://www.jeffreyglasser.com/

[Douglas Fairbank]

I recommend the 21 for use with the 150 / 180 so you have continuous focus range. The extension of the 150 focus mount is 21mm and is not less than that for the 180.

[Slixtiesix]

Thanks Jeff and Douglas (and thank you Douglas for your PM on the shutter of my Sonnar too!).
Continuous focus range was what I was looking for. Seems like I will go for the 21mm.