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the enum should be CAP_PROP_EXPOSURE but isn't work with many API/cameras.

The VideoCapture base class is implemented with different VideoInput classes for different APIs like CAP_DSHOW, CAP_VFW, CAP_MSMF .... Each API might support or not any properties.

The CAP_PROP_EXPOSURE isn't generally supported. You can check OpenCV yourself looking at the setProperty method for any API implementation here (Check the files cap_*.cpp). For example

• Sure VFW, MSMF or V4L do not support CAP_PROP_EXPOSURE
• CAP_DSHOW should support but isn't guaranteed

In addiction the API itself is interfacing with the cam drivers that should respect standards but most often wont.

This means that for example some cameras accepts values for exposure but as a step of pre-defined range like from 1..10 that is not time. Using DSHOW the accepted range is available only internally here or here but you have to use the Debug breakpoints to read.

Conclusion: if you need to control the exposure use driver library of you vision system as suggested by @LBerger