Need some help with my DSLR

I thought it was focused but I guess not lol. It went from blurry to sharp and clear. And yes, it does happen more in low light. But I also noticed it happens when, for example, I was sitting on a plane trying to take pictures of the airport and the planes. I had the camera right up against the window on a super bright day. Wouldn’t do jack.

I’ve tried moving back, forward, zooming out, zooming in. Sometimes zooming out or in helps. Usually though it’s changing the elevation or the pitch of the camera (pointing it up a little more).

Okay, I’ll give this a try. I don’t know how to use MF. I’ll have to look into that, any tips?

Thanks for the help guys. I was starting to think it was my camera but I’m glad it’s just me lol.