\[Lambda] = 1.; k = (2 \[Pi])/\[Lambda]; zr = \[Sigma]^2 k; w = Sqrt[(1/(\[Pi]/\[Lambda] \zr/(zr^2 + z^2)))];
Solve[(w /. {z -> z1}) == wz, \[Sigma]]
w1[wz_, z1_] := Evaluate@FullSimplify[ w /. {\[Sigma] -> 1/2 Sqrt[ wz^2 - Sqrt[\[Pi]^2 wz^4 - 4 z1^2 \[Lambda]^2]/\[Pi]]}];
rayleigh[wz_, z1_] := ((1/2 Sqrt[wz^2 - Sqrt[\[Pi]^2 wz^4 - 4 z1^2 \[Lambda]^2]/\[Pi]])^2 (2 \[Pi])/\[Lambda])

frames = Table[
   Show[
    Graphics[{
      Table[{Black, Line[{{-50, j}, {50, -j}}]}, {j, 30, -30, -10}]
      ,
      Table[{Black, Line[{{-50, j}, {-76, j}}]}, {j, 30, -30, -10}]
      ,
      Table[{If[Abs[j] <= w0, Black, LightGray], Arrow[{{-75, j}, {-100, j}}]}, {j, 30, -30, -10}]
      ,
      Red, Thick , 
      Line[{{-rayleigh[w0, 50], 15}, {rayleigh[w0, 50], 15}}], 
      Line[{{-rayleigh[w0, 50], 14}, {-rayleigh[w0, 50], 16}}], 
      Line[{{rayleigh[w0, 50], 14}, {rayleigh[w0, 50], 16}}],
      Line[{{-100, w0}, {-50, w0}}], Line[{{-100, -w0}, {-50, -w0}}],
      Text[Style["Rayleigh Length\n(Depth of Field)", Bold, FontSize -> 12], {0, 25}]
      }]
    ,
    Plot[{w1[w0, 50], -w1[w0, 50]}, {z, -50, 50}, PlotStyle -> {Red, Red}]
    ,
    Graphics[{
      Gray, Disk[{-50, 0}, {3, 40}],
      Black, Thickness[0.01], Line[{{-75, 40}, {-75, w0 + 2}}], 
      Line[{{-75, -40}, {-75, -w0 - 2}}]
      , Text[Style["Diaphragm", Bold, FontSize -> 12], {-63, 45}]
      }]
    ]
   , {w0, 6, 35, 0.5}];
Dimensions[frames]
ListAnimate[Join[Table[frames[[-1]], 5], Reverse@frames, Table[frames[[1]], 5], frames ] ]