There are actually only 3 most important variables with a camera:
- Shutter Speed - how long the timeframe is to record the image
- Aperture - how much light the lens shines on the image recording plane; the more light the smaller the depth of field
- Focus - where the plane of focus, the area of maximal sharpness, is located
These are the three variables "real" cameras, like a Leica M, will give you most direct access to.
Then, with electronic cameras, one gets also:
- ISO (also called Film/Sensor Speed/Sensitivity)
- White Balance (the current quality of light), but you can also just shoot raw and change that later
With film, usually ISO is limited to whatever you currently have loaded into your camera, and white balance, well you would have to use filters for that one. It should also be mentioned at this point that there is also good old black and white photography that doesnt have color and thus no white balance as such. Also of course IR and UV photography etc.
After that, it depends.
With zoom lenses, one can choose:
- Focal length (angle of view)
With system cameras, one can choose:
- Lens. There are all kinds of differences between lenses. Each lens design differs from the others in its behavior, and due to imperfections reallife lenses differ from each other even if they are the same design.
With some "real" (i.e. large and bulky) cameras, or special lenses, you also get:
- Shift, the ability to change the position of the image plane and the lens horizontally or vertically, allowing to compensate for falling lines
- Tilt, the ability to flip the lens around so its no longer parallel to the plane of the sensor area, thus flipping the plane of focus according to the Scheimpflug rule
Other than that, you have basic things to run the camera:
- On/Off Button and changing batteries (if there are any electronics of some sort, anyway)
- Release Button (unless its one of these 19. century cameras were you just remove the lens cap for a time to take the picture)
- Changing Film (chemical) / Memorycard (eletrical)
And any cameras after the 1950s or so typically have some automations:
- Metering (minimally just automatic selection of Shutter Speed, in more advanced cameras also Aperture, with digital even ISO)
- Autofocus (this one can be super complicated, with many autofocus points, different autofocus operation modusses etc)
- Automatic White Balance (Digital only)
- All kinds of Program modes etc to specify what should be automatted and what should be in control of the photographer
And there is drive mode (Single Picture, Continous Shooting, Self timer etc).
And there is lighting / flash stuff.
And there are filters like polarizers, gradient neutral density filters. A variable neutral density filter, for example, allows you to change shutter speed and aperture with more freedom.
And there are tripods.
And there are remote controls.
And so on and so forth ...
And finally, with digital, or after you digitalized your film - the possibility for photoshop and stuff.
But the core variables are really just three.
