The influence of the individual spectrometer components on the depth dependent sensitivity fall-off (roll-off) in spectral-domain optical coherence tomography (SD-OCT) is investigated. We present a method for the characterization of the roll-off in SD-OCT systems via modulation transfer function (MTF) analysis. The MTF of different image sensors was measured in a newly developed setup, which uses the interference of two coherent light beams. Different contributions, i.e. diffraction, aberrations and sampling effects, to the MTF of a spectrometer of commercially available SD-OCT systems is calculated and is compared with roll-off measurements. The difference was below -2 dB at 90 % of the maximum measurement depth.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.