$("a.fancybox").fancybox({
        type: 'iframe',
        scrolling: 'no',
        autoSize: true,
        fitToView: false,
        afterLoad: function() {
            this.width ='50%'
            this.height ='80%'
        }
    });

<a class="fancybox fancybox.iframe" href="Arrivi.aspx" >
 <asp:Image ID="img_arrivi" runat="server" ImageUrl="~/Immagini/AQUA OBJECTS AQUA GLOBE.png" Width="50px" />
</a>