  Mid-infrared imaging traces the sub-micron and micron sized dust grains in
protoplanetary disks and it offers constraints on the geometrical properties of
the disks and potential companions, particularly if those companions have
circumplanetary disks. We use the VISIR instrument and its upgrade NEAR on the
VLT to take new mid-infrared images of five (pre-)transition disks and one
circumstellar disk with proposed planets and obtain the deepest resolved
mid-infrared observations to date in order to put new constraints on the sizes
of the emitting regions of the disks and the presence of possible companions.
We derotate and stack the data to find the disk properties. Where available we
compare the data to ProDiMo (Protoplanetary Disk Model) radiation
thermo-chemical models to achieve a deeper understanding of the underlying
physical processes within the disks. We apply the circularised PSF subtraction
method to find upper limits on the fluxes of possible companions and model
companions with circumplanetary disks. We resolve three of the six disks and
calculate position angles, inclinations and (upper limits to) sizes of emission
regions in the disks, improving upper limits on two of the unresolved disks. In
all cases the majority of the mid-IR emission comes from small inner disks or
the hot inner rims of outer disks. We refine the existing ProDiMo HD 100546
model SED fit in the mid-IR by increasing the PAH abundance relative to the
ISM, adopting coronene as the representative PAH, and increase the outer cavity
radius to 22.3 AU. We produce flux estimates for putative planetary-mass
companions and circumplanetary disks, ruling out the presence of planetary-mass
companions with $L > 0.0028 L_{\odot}$ for $a > 180$ AU in the HD 100546
system. Upper limits of 0.5 mJy-30 mJy are obtained at 8 $\mu$m-12 $\mu$m for
potential companions in the different disks.
