Manipulate[
Show[
ContourPlot3D[4*x^2+y^2==z,{x,-2,2},{y,-2(Sqrt[2]),2(Sqrt[2])},{z,0,8},BoundaryStyle->None,ContourStyle->{Blue,Opacity[opG]},Mesh->None,AxesOrigin->{0,0,0},ImageSize->600],
(*z=0*)Graphics3D[{Purple,PointSize[0.025],Point[{0,0,0}]}],
ParametricPlot3D[{0.5*Cos[t],Sin[t],1}, {t, 0, 2*Pi}, PlotStyle->{Opacity[b],Thick,Red}],
ParametricPlot3D[{(1/(Sqrt[2]))*Cos[t],(Sqrt[2])*Sin[t],2}, {t, 0, 2*Pi}, PlotStyle->{Opacity[c],Thick,Orange}],
ParametricPlot3D[{Cos[t],2*Sin[t],4}, {t, 0, 2*Pi}, PlotStyle->{Opacity[d],Thick,Green}],
ParametricPlot3D[{(Sqrt[2])*Cos[t],(Sqrt[8])*Sin[t],8}, {t, 0, 2*Pi}, PlotStyle->{Opacity[e],Thick,Cyan}]
],
{{b,0,Text[Style["z=1", RGBColor[0.5,0,0]]]},0,1},{{c,0,Text[Style["z=2", RGBColor[.5,.25,0]]]},0,1},{{d,0,Text[Style["z=4", RGBColor[0,0.5,0]]]},0,1},{{e,0,Text[Style["z=8", RGBColor[.27,.41,.47]]]},0,1},{{opG,0,Text[Style["Graph Opacity", RGBColor[0,0,0.5]]]},0,1},
ControlPlacement->Left
]