Do (all) cinema lenses get slower as you focus closer?

[Matt W.]

Interesting....what exactly is the concept behind lenses that don't breath (do they simply zoom out a bit as you focus closer, or is it much more complicated?), btw, and when was that introduced? And how does cam focusing work versus a helical?

Electronic focus sounds exciting; the USB systems for the 5D are already pretty cool for no-budget work.

[Rob Ruffo]

Interesting....what exactly is the concept behind lenses that don't breath (do they simply zoom out a bit as you focus closer, or is it much more complicated?), btw, and when was that introduced? And how does cam focusing work versus a helical?

Electronic focus sounds exciting; the USB systems for the 5D are already pretty cool for no-budget work.

The 5D system is worse than focussing by hand as it steps like crazy. Jacek's system is a whole other thing. It's awesome.

[Jacek Zakowicz]

Thank you Rob, I'm glad you liked it
Matt helical is based on threaded rings so that, by definition, is a fixed pitch.
Cam system is a slot machined in a ring and a key that fits in it and guides the glass housing. By varying the slope of the slot you can adjust pitch (travel rate) at will.
The cam system is a necessity for zoom lenses as the optical design determines the movement of the glass.
It was adapted for focus control because of the flexibility and longevity it offers....