[en] In this paper the scaling spectra of finite-size Ising model corner transfer matrices (CTMs) are studied at criticality, using the fermion algebra. The low-lying eigenvalues collapse like 1/logN for large N as predicted by conformal invariance. The shift in the largest eigenvalue is evaluated analytically using a generalized Euler-Maclaurin summation formula giving πc/6 logN with central charge c = 1/2. The spectrum generating functions, for both fixed and free boundary conditions, are expressed simply in terms of the c = 1/2 Virasoro characters χΔ(q) with modular parameter q = exp(-π/log N) and conformal dimensions Δ = 0, 1/2, 1/16