iPhone SE (2nd Generation)
The iPhone SE 2 has an aperture ƒ/1.8 on the rear and ƒ/2.2 aperture on the front-facing FaceTime HD camera.
iPhone SE (1st Generation)
The iPhone SE camera has an aperture of f/2.2.Apple has maintained iSight cameras with apertures of f/2.2 since the iPhone 5s. Since the iPhone SE shares the same camera as the iPhone 6s, the aperture has not changed.
Previous models such as the iPhone 5, iPhone 5c and iPhone 4s had a smaller aperture at f/2.4. Increasing the size of the aperture allows more light to reach the image sensor, improving low light sensitivity.