Nikon D3400 Triple Lens Parent's Kit Owner's Manual

114 P, S, A, and M Modes

Recompose the 
photograph.
Keeping the 

A (L) button 

pressed, recompose the 
photograph and shoot.

A

While exposure lock is in effect, the following settings can be adjusted 
without altering the metered value for exposure:

Programmed auto

Shutter speed and aperture 

(flexible program; 

Shutter-priority auto

Shutter speed

Aperture-priority auto

Aperture

The metering method itself can not be changed while exposure lock is 
in effect.