A surface plasmon resonance instrument and measuring method, in which a lens collimates light into a light beam, a prism propagates the collimated light beam at a single propagation angle and with internal reflection on a face of the prism, and an analyzer processes the collimated light beam from the prism. The face of the prism is configured to receive a surface plasmon resonance sensor and at least the first lens and the prism are aligned on a single optical axis.