contour_plot: can I get a logarithmic axis?

Hello,

I have the following code:

   assume( x >= 0, y >= 0, C >= 0 );

   ytp(x,C,d,t) := x * ( ( 1 + 2 * C / ( 1 + d^2 + x ) )^2 + ( t - 2 *
C * d / ( 1 + d^2 + x ) )^2 );

   contour_plot(
      ytp(x,3,d,0), [d,-20,20], [x,0,40], [grid,200,200], [legend,"Y"],
      [gnuplot_preamble, "set key outside; set title 'Traveling plane
wave, C = 3'"] )$

The last plot looks gorgeous to me, but I want to explore the possible
Y values. Unfortunately If I try this:

   contour_plot(
      ytp(x,3,d,0), [d,-20,20], [x,0,1010], [grid,200,200], [legend,"Y"],
      [gnuplot_preamble, "set key outside; set title 'Traveling plane
wave, C = 3'; set cntrparam levels 10"] )$

The center feature is barely noticeable, which is not what I want. I
decided to try to use a logarithmic scale for my "y-axis" (really my
x). So I tried using the option [logy] and got nothing as output.
Decided then to try "set log y" in the gnuplot_preamble and again
nothing.

Is this feature available with contour_plot? or am I missing something?

Thanks for the help

Andres