I would like to know if there is a difference in mic capsule between the SM31FH and the SM35. I need a mic for vocals.
Yes, there is a difference. Here are the primary differences:
SM35 has 9 dB less output level - not critical for singing because the mic is close to the mouth.
SM35 has a tighter polar pattern. This means less feedback when use for live music.
SM35 has a better bass response and a better high end response. It has better fidelity for music.
Bottom line: SM35 should sound better for vocals.