How to make fancybox pop up images of same height and width

Changing size of popup box in jquery fancy box images:

jQuery(".fancybox").fancybox({    
     closeBtn  : true,
     arrows    : true,
     fitToView: false,
     nextClick : true, 
     beforeShow: function () { 
       this.width = 1200; 
       this.height = 400; } 
});