My camera is always at a 50mm focal length whenever my subject is in focus.

Sorry but a 50mm prime lens is 50mm no matter the focus. Sigh. So many things to respond to. For anyone confused about this stuff, I highly recommend the DPReview Beginners Questions forum. I went here when I was switching from film to digital. Asked some remarkably uninformed questions (looking back at them). Responders were unfailingly polite and encouraging. Go check it out.

[edit] yes it’s possible to have a lens change effective focal length as focus changes. This is called ‘focus breathing’. It tends to be an issue with zooms not primes. It’s a major issue for cinematographers — and not the kind of thing a beginner would care about. [/edit]