Canon EOS 750D Instruction Manual page 169

The exposure compensation amount will remain in effect even after you
set the power switch to <2>.
You can also set flash exposure compensation with [Built-in flash
settings] in [z1: Flash control] (p.176).
A Locking the Flash Exposure (FE lock)K
If the subject is on the side of the frame and you use flash, the subject may
turn out to be too bright or dark depending on the background, etc. Use FE
lock in such a case. After setting the proper flash exposure for the subject,
you can recompose (put the subject toward the side) and shoot. This
feature can also be used with a Canon EX-series Speedlite.
* FE stands for Flash Exposure.
Each time you press the <A> button, a preflash is fired and the
required flash output is calculated and retained in memory.
Press the <D> button.
1
The built-in flash will be raised.
Press the shutter button halfway and
look in the viewfinder to check that
the <D> icon is lit.
Focus on the subject.
2
Press the <A> button.
3
Aim the viewfinder center over the
subject where you want to lock the flash
exposure, then press the <A> button.
The flash will fire a preflash and the
required flash output is calculated
and retained in memory.
In the viewfinder, "FEL" is displayed
for a moment and <d> will light up.
D Using the Built-in Flash
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