Wie kann ich beim iterativen Plot / Feigenbaumdiagramm einen Spy ergänzen?

% arara: lualatex
\author{stefan_k}
\documentclass[border=10pt]{standalone}
\usepackage{pgfplots}
    \usetikzlibrary{spy}
\usepackage{luacode}
\begin{luacode*}
  function logistic()

    local function map(r,x)
      return r*x*(1-x)
    end

    for r = 2.5,4,0.005 do
      x = 0.1
      for i = 1, 200 do
        x = map(r,x)
      end
      for i = 1, 250 do
        x = map(r,x)
        tex.sprint("("..r..","..x..")")
      end
    end
  end
\end{luacode*}
\begin{document}
\begin{tikzpicture}[spy using outlines={rectangle, red, magnification=5,
size=1.5cm, connect spies}]
\begin{axis}[tick label style={font=\tiny}, axis lines=middle]
        \edef\logisticplot{\noexpand\addplot [color=black!10, mesh, only marks,
      mark size = 0.05pt, opacity = 0.1] coordinates{ \directlua{logistic()} };}
    \logisticplot
\draw[blue] (axis cs: 0,0) -- (axis cs: 2,0.5);
\end{axis}
%
% Problem: 
%
%\spy [blue, size=0.5cm] on (axis cs: 3.55,.5) in node [right] at (0,-5.25); 
%
%
%
\end{tikzpicture}
\end{document}