I was attempting to capture the full moon tonight using my Canon EOS R50 mounted on a tripod. I had a telephoto lens attached to the camera via a Canon adapter, as this lens was originally designed for my father’s Canon Digital Rebel and had an incompatible mount for the R50.
While zoomed in on the moon to fill the frame, I observed an unexpected behavior: the camera appeared to automatically zoom the image back out. I was under the impression that the camera itself lacked the capability to adjust the zoom setting, but the viewfinder clearly indicated a change in magnification
Update: In case it is important, the lens has image stabilization built in, but I have it turned off as it lets me set focus and recompose better.
I can’t say for sure, but I think I had my hand on the zoom ring. The moon will still be full enough tonight perhaps I will try again. I looked up “Focus Breathing” and I am not sure what it is really talking about.
Essentially it’s a small to moderate shift in amount of zoom because of the movement of the internal elements during focusing. I would just look up focus breathing on YouTube and see some examples and if it matches what you noticed.