Re: sn-3 question
The mechanism is inherently the same between the older ERGO and the newer slimmer ERGO.
What they do have new is a faster focus ERGO that runs the range of adjustment in a fraction of a turn instead of rotating the objective a complete turn (haven't had hands on yet, but I do have one being built).
I am unaware that any of the ERGO's changes are "upgradable" as in retrofitting them to a previous model. If the fast focus is as good as I'm hoping and is retrofittable, my others will be getting it too.
The new internal bubble kicks ass and can be added to most exisiting SN3's.
It is my understanding the pushbutton illumination can't be swapped into older rheostats. No consequence, as I prefer the rheostat.