missing focus- is it the camera or the lens?

I've noticed lately that when I lock focus and shoot, I look at the photo and it missed focus. What's up with that?

Can you post an example?

anitaw2 wrote in post #19280769
I've noticed lately that when I lock focus and shoot, I look at the photo and it missed focus. What's up with that?

Have you done any controlled testing? There isn't enough information for us to go on to help you. Lock it on a tripod shoot a test subject and see what happens from there.

Is your camera focus largely 'factory setting', that is, the location of the AF zone(s) which light up lie all over the viewfinder?
In factory configuration, the camera ASSUMES what should be in focus, so what AF zones light up are NOT way YOU WANT, necessarily, they are what the camera decides to focus upon (perhaps the highest contrast edges in the scene).

You can control which AF zones are used for focus, so that the focus point lies on top of your 'most important location' that you have chosen.

Yeah, we need way more information if you want help. It might not even be a focus issue. What camera and what lens? What tests have you done? Examples please, with EXIF.

So many reasons.
Cameras are not perfect.
Difficult subject - over simplification: not enough contrast.
Atmosphere - heat 'shimmer'
Subject moved.
Poor choice of AF point (Some AF points are sensitive to horizontal, some vertical, some both)
Incorrect focus limiter setting, or subject closer than minimum focus distance.
Incorrect Image Stabilisation mode or use.
Camera or lens faulty. Many possibilities here.
- Either lens or camera AF system faulty.
- Lens elements have moved or tilted.
- IS or IBIS problem.
- Camera AF sensor moved. (If it is a mirrorless camera or you are using Liveview forget this possibilty)

Are you sure it's missed focus. Subject movement and camera movement can be challenging to tell apart from missed focus.
If there is something in the image that is in focus and the area in focus is at a different distance to the subject, it's more likely missed focus.

Make sure you're not set for AI focus or AI servo focus. In my cameras, they will often refocus when you change your aim.

Or alternatively, you should be in ai servo but aren’t and your subject moved.

Without more info we cannot help.