Лупа

var isMobile = /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent);
if (!isMobile && jQuery().zoom) {
    $('.gr-image-zoom').zoom({
        magnify: 1,
        duration: 10,
        onZoomIn: function(){
            $(this).parent().addClass('hide_small_pic');
        },
        onZoomOut: function(){
            $(this).parent().removeClass('hide_small_pic');
        },
        callback: function(){
            var $zoomImg = $(this);
            var zoomImgHeight = Math.floor($zoomImg.height());
            var zoomImgWidth = Math.floor($zoomImg.width());
            var floatHeight = Math.floor(20 * zoomImgHeight / 100);
            var floatWidth = Math.floor(20 * zoomImgWidth / 100);
            var prevWidth = Math.floor($(this).prev().outerWidth());
            var prevHeight = Math.floor($(this).prev().outerHeight());

            var zoomFloatHeight = zoomImgHeight + floatHeight;
            var zoomFloatWidth = zoomImgWidth + floatWidth;
            var finalHeight = prevHeight+floatHeight;
            var finalWidth = prevWidth+floatWidth;

            if (zoomFloatHeight<=prevHeight-floatHeight || zoomFloatWidth<=prevWidth-floatWidth) {
                $(this).parent().addClass('hide_big_pic');
            };

            if (zoomImgHeight<=prevHeight || zoomImgWidth <=prevWidth) {
                $zoomImg.css({
                    'width': finalWidth,
                    'height': finalHeight
                });
            }
        }
    });
};