Picked up a Kern Switar 16/1.8 C-mount lens from a 16mm camera a few days ago and played with it a bit. Here's some fiddling with it:

Kids, Dogs, and Mangy Puppies on Vimeo

Kevin how do you work out the 16mm to 83mm equivalent, E-T-C at X 2.6

I make that the lens is 41.6 equivalent. Nice video.

it's labeled 16mm, so bare, it'd be 32mm equivalent.

With ETC, 16 x 2 x 2.6 = 83.2... or at least that's what my math is thinking.

Obviously the shots with vignetting are without the ETC engaged.