I built this monopod from the three legs of a compact-tripod. I use a Y shaped yoke as a lens rest. Each segment is 8" long when collapsed and doubles in length when opened, so the overall length varies between 8" and 54". One segment is useful while seated at a table, two segments while in stadium seating, and three segments while standing.
I use it frequently, especially with long lenses. I find I often use two segments while I'm seated in a theater, auditorium, or otherwise. On a Cabaret table one segment works nicely. It easily fits in my small camera bag.
Dave in Iowa
PS the top photo shows the three legs removed from the compact-tripod (Wal-Mart) and the 1/4-20 coupling nuts and hanger bolts used to couple them. Coupling nuts were epoxied into the foot of each segment and hanger bolts were epoxied into the top of each segment. I added rubber feet later.
I'm considering building a similar "stealth" monopod from an extendable walking cane with a "Derby" handle which will act as a lens rest.
It should be useful in museums & theaters (when I don't have the camera bag.)