%
%
% This function displays the impulse response for a coherent
%
%
% The first bit calculates the Fresnel diffraction to the lens
%
% In these simulations, we choose to work in units of wavelength*2*10^3
%
%
range=0.2;
npoints=512;
step=range/npoints;
lamda=5*10^(-4);
objectdistance=10;
imagedistance=10;
focallength=5;
scale=-range/2:step:range/2-step;
ftscale=(npoints/range^2)*scale;
[x,y]=meshdom(scale,scale);
[fx,fy]=meshdom(ftscale,ftscale);
%  Assume that the input is a delta function
%
fi=zeros(npoints);
fi(npoints/2,npoints/2)=1;
dt=fftshift(fft2(fftshift(fi)));
ff=pup(-lamda*imagedistance*fx,-lamda*imagedistance*fy);
ft=ff.*dt;
fa=fftshift(ifft2(fftshift(ft)));
figure(1);
colormap('hot');
axis('square');
imagesc(scale,scale,abs(fa));