  The velocity Slice Imaging technique has revolutionised electron molecule
interaction studies. Multiple electrostatic lens assemblies are often used in
spectrometers for resolving low kinetic energy fragments. However, in a
crossed-beam experiment with an effusive molecular beam, the extended source of
ion generation due to the presence of the background gas creates artefacts on
the momentum images as we try to magnify them beyond a certain size. Here, we
present a systematic study of this effect on momentum imaging and the solutions
to address this issue by background subtraction with suitable magnification.
Additionally, we demonstrated that a supersonic molecular beam target helps
minimise these artefacts in the image magnification by reducing the background
signal. These systematic findings may bring valuable insight into the
investigation of low kinetic energy release processes involving electron
impact, ion impact, and merge beam experiments with large interaction volumes
where high magnification is needed.
