High shutter speed with low frame rate and auto exposure

Question

Created Aug ’25

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Hi there,

I want to set the iphone camera to "S mode, or Shutter Priority" in camera terminology. Which is a semi-auto exposure model with shutter speed fixed, or set manually.

However, when setting the shutter speed manually, it disables the auto exposure.

So is there a way to keep the auto exposure on while restrict the shutter speed?

Also, I would like to keep a low frame rate, e.g. 30 fps. Would I be able to set shutter speed independent of frame rate?

Here's the code for setting up the camera

Best,

Answered by Alundor in 858475022

Also found High frame-rate doesn't guarantee fast shutter speed. In my case: I have 60 fps with 1/30 shutter speed:

This is actually completely normal and possible! Here's why:

Frame Rate (60 fps): This means a new frame is captured every 1/60 second (≈16.67ms) Shutter Speed (1/30 second): This means each individual frame is exposed for 1/30 second (≈33.33ms)

How this works: The camera sensor can be exposing one frame while simultaneously reading out the previous frame. This is called rolling shutter operation, which is standard in CMOS sensors.

Answer 1

Alundor OP

Sep ’25

Accepted Answer

Also found High frame-rate doesn't guarantee fast shutter speed. In my case: I have 60 fps with 1/30 shutter speed:

This is actually completely normal and possible! Here's why:

Frame Rate (60 fps): This means a new frame is captured every 1/60 second (≈16.67ms) Shutter Speed (1/30 second): This means each individual frame is exposed for 1/30 second (≈33.33ms)

How this works: The camera sensor can be exposing one frame while simultaneously reading out the previous frame. This is called rolling shutter operation, which is standard in CMOS sensors.