Need some help for FFT2 of an Image

Hi all,

 I am a beginner in matlab and i seriously need your help.

MY PROBLEM: 

  I have a grayscale image(1024 X 1280) of a pyrovalve(a valve used in
rocket engines, looks like a small piston cylinder arrangement). I was
asked to do fourier analysis(2D) on this image. For that i took FFT2 of the
image. I can get the absolute frequency values. I have to make a 3D plot of
the frequency magnitude. When i used mesh(abs(fft2(I))), i can see a 3D
plot, which is flat. The x, y axes taking the no. of pixels and z axes
taking the magnitude. But i need to get a Sombrero plot(a mexican hat). How
can i get that plot? And i have a question regarding the "Spatial
frequency". How can i calculate spatial frequency from pixels?. I believe,
i need to take the frequency on x and y axes and magnitude of frquency on z
axes to get a sombrero plot.

Does my image really produce a sombrero plot or not?

Can anyone rectify my problem and explain me clearly.

Waiting for a reply,
shashi