We report on a tunable optical bandpass filter with precise and independent control of its optical bandwidth and center wavelength. The optical filter is based on a double-pass monochromator configuration and a variable-aperture microelectromechanical systems (MEMS) reflector with two blocking micromirrors that manipulate the optical passband. The MEMS reflector is fabricated on the sidewalls of (110) silicon-on-insulator material by a combination of wet etching and deep reactive ion etching. The l-dB optical bandwidth is continuously tunable from 3.65 to 6.35 run by changing the position of the blocking micromirrors with lateral combdrive actuators. The center wavelength can be accurately controlled within a 30-nm spectral range by rotating the diffraction grating and/or changing the center location of the variable aperture with the combdrive actuators. The measured group delay variation across the passband was negligible.