Exposure Compensation with Manual Mode - FZ150

Hi everyone,

I'm practicing to shoot a waterfall in the daylight. I want the blurry effect on the falls so I set my shutter speed to 8 seconds. To compensate, I set my aperture to f7,2 to reduce the amount of light and it doesn't matter because I don't need a big depth of field.

Even with these parameters, my picture is too bright. I would like to use the expose compensation control, but it seems impossible in manual mode. The camera set it up automatically. Is it possible to control it by any chance ?

Thank you in advance