I am strictly an amateur, and I do this as my hobby. Having said that, the quality ranges from not bad to remarkably good (even if I say so myself!)
I started with Super VHS, progressed to a 3-chip Canon XM1 digital camera in 2000, and to a Canon XH-A1 high-definition camera in 2007. As for my regular collaborators, Laurie Golden uses a Canon like mine while TWR used a Sony FX1 until 2010 when he replaced it with a Sony FX1000, both of which are 3-chip high definition cameras. We (almost) always use tripods (so no sea-sickness pills required) and external microphones (so you can hear what’s going on quite clearly).
I use a powerful video editing package on my computer (Avid Liquid) to select and compile the programmes, add sub-titles and so on. Basic details of locomotives and locations are given in unobtrusive captions and in sleeve notes. There’s no banal commentary, no distracting music (except sometimes for the opening and closing titles), and no ham-fisted attempts to disguise these scenes as other than what they are: dramatic, contemporary records of steam locomotives that continue to defy the scrap yard!