I have often wondered what the purpose of monopods is. It seems to me that they remove only two degrees of freedom out of three possible degrees of freedom of camera shake. And the situation is even worse for telephoto lenses, where one of the removed degrees of freedom isn't problematic, so that's one out of two removed. I usually don't need stabilization provided by a tripod unless it's for long exposures (where a monopod probably doesn't help) or tele photography (where I suspect monopod isn't that good either).
Camera shake can be, using aircraft terminology:
- Pitch shake: this is removed by a monopod
- Roll shake: this is removed by a monopod
- Yaw shake: this is completely unaffected by a monopod
When using a telephoto lens, my understanding is that the yaw and pitch shake become more problematic and the problematicity of roll shake is not that big. So, when taking a tele photograph, you are affected mainly by:
- Pitch shake: this is removed by a monopod
- Yaw shake: this is completely unaffected by a monopod
So, when taking a tele photograph, a monopod removes only one of the two problematic degrees of freedom of camera shake.
Based on this, my intuition is that a monopod offers probably around one additional stop in possible exposure time when taking tele photographs, if even that. Is this intuition correct? Are monopods really useful in practice to be used with telephoto lenses? How much extra stops do they offer in reality for tele photography?
A good image stabilizer can offer 3-4 stops of advertised improvement, and I genuinely believe it achieves most of that for intermediate exposures (not short or long), having tested the IS of Canon 55-250 mm lens.
Related: How much benefit can one expect from a monopod? ...although the existing question is for general purpose photography, not for tele photography. Here I'm interested only in answers related to tele photography, such as photographing birds or the moon with a monopod and without image stabilization (which I suspect won't be a good idea).