Photoshop :: Ragged Shadows In 3D Images / Meshes Created From Greyscale?

I am having a problem creating smooth 3D images.I have been taking a 16-bit greyscale image with a various domes and other shapes with systematic gradations of greyness 'impressed' onto it. From this, I use the "create 3D mesh from greyscale" to create a surface whose depth is based on the values in the 16-bit greyscale image: this greyscale image becomes the "Background Depth" layer in the 3D image. I then add a Background layer (that exactly matches the greyscale image) to the 3D image, which will determine how the 3D shape will be coloured.
 
I then force ray tracing using the "Quality: " "Ray Trace Draft" or "Ray Trace Final" and the result is a 3D surface with some shadows. Okay so far, BUT the surface is a bit pitted, a bit ragged, not smooth, the shadows have jagged bit in - it's just not very good, in fact, it's unusably poor.  Even if I apply some filtering to the greyscale image to smooth out any nasty discontinuities there may be in it, the final 3D surface is still pitted, with jagged shadows etc.
 
If I look at a wireframe version of a 3D image, it is clear that the resolution of the starting image is better than that of the wireframe image: there are several points in the original image to each point on the wireframe image (that is to say, each vertex in the triangles that make up the wire frame image is several points away from each other vertex).
 
When I look at the sample images in tutorials etc they look incredibly smooth and appealing. Why cannot I produce the same quality of image?  Are there some settings in the Edit->Preferences->3D panel that I need to reset?  Some way of increasing the number of triangles in the wireframe model?
 
I have posted a sample of the grayscale image, and a sample of the 3D image that this greyscale image produces when converted into a mesh. (I've saved them as JPG files, which forces the 16-bit greyscale into 8-bit mode. But the original conversion to a mesh was performed using a 16-bit greyscale image).

I am using windows 7 on an HP Pavilion Laptop, using OpenGL to draw the graphics.