We consider the Ising model at its critical temperature with external magnetic field ha 15/8 on aZ 2 . We give a purely probabilistic proof, using FK methods rather than reflection positivity, that for a = 1, the correlation length is ≥ const. h −8/15 as h ↓ 0. We extend to the a ↓ 0 continuum limit the FK-Ising coupling for all h > 0, and obtain tail estimates for the largest renormalized cluster area in a finite domain as well as an upper bound with exponent 1/8 for the one-arm event. Finally, we show that for a = 1, the average magnetization, M(h), in Z 2 satisfies M(h)/h 1/15 → some B ∈ (0, ∞) as h ↓ 0.