VideoCapture with grayscale camera

Hello I´m begginer on OpenCv I have a grayscale video camera ELP-USBFHD01M-SFV B/W, 120fps at 480 pixels with picture format MJPEG and YUY2 I need to capture an image almost at 60 FPS. One of my jobs is detect circles using HougCircles, using cvtColor(frame, edges, COLOR_BGR2GRAY) to convert the image to grayscale. I´m loosing a lot of time adquiring and suposed RGB image and converting it to grayscale. Anybody knows how to adquire the image directly in grayscale? Thanks for your answers