  Context. Modern space telescopes are currently providing high-precision light
curves for a large fraction of the sky, such that many new variable stars are
being discovered. However, some stars have periodic variability with periods of
order minutes and require high-cadence photometry to probe the physical
mechanisms responsible. A cadence of less than a minute is often required to
remove Nyquist ambiguities and confirm rapid variability which forces observers
to obtain high-cadence ground-based photometry. Aims. We aim to provide a
modern software package to reduce ground-based photometric time series data and
deliver optimised (differential) light curves. To produce high-quality light
curves, which maximise the amplitude signal-to-noise ratio of short-period
variability in a Fourier spectrum, we require adaptive elliptical aperture
photometry as this represents a significant advantage compared to aperture
photometry using circular apertures of fixed radii. Methods. The methodology of
our code and its advantages are demonstrated using high-cadence ground-based
photometry from the South African Astronomical Observatory (SAAO) of a
confirmed rapidly oscillating Ap (roAp) star. Furthermore, we employ our
software package to search for rapid oscillations in three candidate roAp
stars. Results. We demonstrate that our pipeline represents a significant
improvement in the quality of light curves, and we make it available to the
community for use with different instruments and observatories. We search for
and demonstrate the lack of high-frequency roAp pulsations to a limit of
$\sim$1 mmag using B data in the three Ap stars HD 158596, HD 166542 and HD
181810. Conclusions. We demonstrate the significant improvement in the
extraction of short-period variability caused by high-frequency pulsation
modes, and discuss the implication of null detections in three Ap stars.
