it's called 'faceting' (or at least thats what I call it :-) & is a direct result of the number of polygons used in an object. The more polygons you add to a model the smoother the appearance but there is a corresponding increase in file size The attached screen cap from lightwave is an extreme example but will illustrate the problem all modellers have in balancing poly count with file size. left= 17,664 polys 414K (about 2megs converted to obj) right= 288 polys (6.4K about 30K converted to obj)