I learned to focus lights on a center-extension a-frame ladder (what we called them). It felt safe once you locked your legs over the top, as was said you could sit there for a long time. (There's actually a picure of me on one in my High School yearbook.) There was one that I used that was about 30' tall, and had enough
play in the top section that you could move yourself several feet along a
batten.... plus it had wheels. A
bit scary, but very efficient.
When looking at currently available ladders for a newly renovated theater, it appears that the only thing that is
OSHA approved is either a
scaffold, or a Genie lift (or other brand...). They still make what look like center extension a-frame ladders, but they are now called "trestle ladders"... they are designed to support
scaffold planks on the extension sections (using two of them.) According to the manufacturer, they are explicitly not to be used as we used to. This is making it very hard to get anything that the school will approve of for the new theater... powered lifts are too expensive (and they won't let students use them anyway), and they're not used to buying scaffolding. So, at the moment, we put a 16' ladder on some 4' platforms to focus
(We used to have a
Tallescope, but it was pretty trashed, and was junked as part of the renovation.)