u/GloomyFollowing5180

I am very confused. I am using DOF preview on my r6 iii with the RF 50mm 1.4 and I do not understand why it is that when I set my apature, say F8 (not wide open) , and then press the shutter, the aperture goes from f8, to then wide open then back to F8. It makes no sense, if I want f8 before and after my shot, why does it open just after the exposure.

I ask mainly because I find it strange to take an image at F8, then just after have my live veiw go blurry then in focus as it stops back to f8 from 1.4, but now I am also curious.

If someone more advanced could explain I would be grateful.