Well, if you want to learn everything there is to know about the camera, I would get a job in a rental house and soak up everything you can about the camera. I personally would not worry about that as much but rather use my time to learn all you can about lighting, lenses and camera movement. Also, framing, deciding how best to give the director what he wants, what lens, what focal lengths or go with a zoom and if so, which one, cool or warm and where to set the camera for the most effective background and foreground as well as where to place your subject within the frame to make the strongest statement for the circumstance.
Lighting is the PREMIERE job of a Director of Photography. It is a technical task that must be done with the artistry of the director's vision. What lights do you need, pars, kinos, fresnels, nooks, maxies. and on and on, what gels, where do you put the lights, the flags, what do you set the veriacs at, how do you create a comprehensive lighting scheme that helps complement the emotion aspect of any given scene but also works as a whole while at the same time can be set up within the given schedule.
There is also the question of learning film stocks, which are going to be the best choice for a given project. Then there's the question of when to manipulate the film, when to push the processing, when to pull, when to skip bleach, ect. All this also applies to electronic acquisition, digital which is the standard. Those images will be manipulated in a computer but the decisions are basically the same. The camera you choose, if you're given a choice, makes a difference as does the format. This is probably even more important in a digital format. Then, more often than not, the film is scanned and manipulated digitally.
THEN, there is the human factor, who do you hire or request for the lighting/camera department, can you keep them motivated and doing their best work, how do you handle problems and mistakes, when to you push and when do you back off. How are you going to deal with a difficult actor or director or producer, how do you broach a disagreement with a director over technical or artistic decision. The cinematographer is second in command under the director. He/she has a tremendous amount of responsibility and it is a very tough job with a lot of pressure that goes along with it. A good DOP is worth his weight in platinum so a smart director treats them with the respect they deserve. If you choose to pursue that career, you have much to learn. You probably know a lot know with 25 years experience, but if you what to move to DOP, you'll need to learn more. I would suggest you start by working as a DOP on low/no budget pictures and TV shows, work for free on some stuff to build your reel and look for opportunities for better work, At first you'll be working as a cameraman to pay the bills some times and a DOP for ridiculously low pay or no pay some of the time to build you resume' Just my opinion, take it for what it's worth.