A particle-optical apparatus, such as an ESEM.RTM., for simultaneous observing a sample with particles and photons. A pressure limiting aperture (PLA) is placed in a diaphragm between the objective lens of the ESEM.RTM. and the sample position. The distance between the sample position and the aperture is sufficiently small to allow a large collection angle of the photons through this aperture. A mirror is placed between the diaphragm and the objective lens. Due to the large collection angle for photons a large NA is achieved. The small distance between sample position and aperture also result in less scattering of electrons than occurs in ESEM's where a mirror is placed between aperture and sample position, as the electrons have to travel through only a limited length in a high pressure area. Embodiments describe combinations where e.g. an immersion lens is used.