import math


def fov_to_cell_size(fov, im_size):
    """Evaluate image pixel size for given FoV and number of pixels.

    Args:
        fov (float): Field of view, in degrees
        im_size (int): Image size (1D) in pixels.

    Returns:
        float: pixel size, in arcsec.
    """
    r_max = math.sin(math.radians(fov) / 2)
    inc = r_max / (0.5 * im_size)
    return math.degrees(math.asin(inc)) * 3600