.jumbotron {
    /*position: relative;*/
    /*background: none;*/
}

    .jumbotron:after {
        content: "";
        display: block;
        position: absolute;
        top: 0;
        left: 0;      
        background-image: url('../image/image1.jpg');
        background-repeat: no-repeat;
        background-position: center;
        background-size: cover;
        width: 100%;
        height: 100%;
        opacity: 0.4;
        z-index: -1;
    }