def calc_t_duration(n_group, n_int, n_reset, t_frame, n_frame=1):
    """Calculates duration time (or exposure duration as told by APT.)

    Parameters
    ----------
    n_group : int
        Groups per integration.
    n_int : int
        Integrations per exposure.
    n_reset : int
        Reset frames per integration.
    t_frame : float
        Frame time (in seconds).
    n_frame : int, optional
        Frames per group -- always one except brown dwarves.

    Returns
    -------
    t_duration : float
        Duration time (in seconds).
    """
    
    t_duration = t_frame*(n_group*n_frame + n_reset)*n_int
    return t_duration