  Filaments are an important part of star-forming interstellar clouds. Theie
properties hold clues to their formation mechanisms and role in the
star-formation process. We compare the properties of filaments in the Orion
Molecular Cloud 3 (OMC-3), as seen in mid-infrared (MIR) absorption and
far-infrared (FIR) dust emission. We calculated optical depth maps of the OMC-3
filaments based on the MIR absorption seen in Spitzer data and FIR dust
emission observed with Herschel and the ArT\'eMiS instrument. The widths of the
selected OMC-3 filament segments are in the range 0.03-0.1 pc, with similar
average values seen in both MIR and FIR analyses. Compared to the widths, the
individual parameters of the fitted Plummer functions are much more uncertain.
The asymptotic power-law index has typically values p~3 but with a large
scatter. Modelling shows that the FIR observations can systematically
overestimate the filament widths. The effect is potentially tens of per cent at
column densities above N(H$_2$) ~ $10^{22}$ cm$^{-2}$ but is reduced in more
intense radiation fields, such as the Orion region. Spatial variations in dust
properties could cause errors of similar magnitude. In the MIR analysis, dust
scattering should generally not be a significant factor, unless there are
high-mass stars nearby or the dust MIR scattering efficiency is higher than in
the tested dust models. Thermal MIR dust emission can be a more significant
source of error, especially close to embedded sources. The analysis of
interstellar filaments can be affected by several sources of systematic error,
but mainly at high column densities and, in the case of FIR observations, in
weak radiation fields. The widths of the OMC-3 filaments were consistent
between the MIR and FIR analyses and did not reveal systematic dependence on
the angular resolution of the observations.
