Which camera settings change focus, and when do I need to refocus?

Question

I shoot at night with a Nikon D5600 and the AF-P DX 18-55mm VR kit lens. When autofocus struggles in low light, I focus on a different well-lit subject at about the same distance, then recompose and take the shot.

If I change settings after that—such as image quality, picture style, PSAM mode, shutter speed, ISO, exposure compensation, or aperture—do I need to autofocus again, or will the focus distance stay where it was?

More generally, which kinds of settings actually change the lens focus distance and require refocusing, and which do not? Also, if I autofocus once and then switch autofocus off, can I assume focus will stay fixed unless I change a focus-related setting or move the focus ring?

user57929 · Accepted Answer

None of the settings you mention will change the lens focussing - but changing the focal length on a zoom lens definitely will.

Late edit
Now we know what lens we're talking about - the kit 18-55mm, even changing focal length isn't going to me much of a problem with that lens. Almost by accident of design rather than by intent, it's almost parfocal anyway [it doesn't change focus based on 'zoom'].

After some further clarification in the question body - the OP is using AF Lock, rather than back button focussing, 'AF ON'.
Aside from the above, that nothing except changing focal length will really affect focus, it would seem the solution would be to use AF ON [or the other two manual focus alternatives below]. Instead of trying to use the button as an override, use it to focus when needed.

^{Previous answer, partially obviated by comments & question edit}
This is almost moot unless you switch off the AF mechanism in the half-press by one of the following methods.

With standard settings, every time you half-press it will refocus, so anything else you do in between will require another half-press, focus, shot. You have apparently been overriding this using AF Lock.
Otherwise, you cannot avoid the half-press no matter how fast you do it, it will check or refocus every time you press it, unless you switch it off.

The way to avoid this is by using back button focus instead, so only pressing the back button will focus, pressing the shutter will simply take the photo.

You can set this up in settings - I also moved mine to the Quick menu to save having to dig for it every time. You can lock focus &/or exposure, jointly or separately. This is from the D5500 manual. I doubt the D5600 is much different…
To clarify, after comments & question edit, 'back button focus' is termed 'AF ON' by Nikon. This is then the only button that will instigate focus. Using AF Lock is an override, only active whilst the button is pressed; otherwise standard half-squeeze will initiate focus.

Alternatively, if your lens supports it, you could just flip the physical switch on the side from M/A to M.
If not, you can disable it in the main shoot menu on the rear of the camera.

Which camera settings change focus, and when do I need to refocus?

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