# Half-max isocline in log-log scale

I have a function and I would like to contour plot with half-max in log-log (in base 10 )scale.

   f[i1_,i2_]:= 87.6293 + 1.30282*10^6/( 194.574 + 8439.54/(1 + 3.2176*10^9 i1^3.8546) + 18567.7/(  1 + 157.95 i2^1.39834))


and half max is

h=3380.54


This kind of plot is expected

Can someone help me out. Thanks in advance.

Create a helper function g to transform from log to natural space, then plot contours of that function. Using your definition of f from OP:
Clear[g]