The meteors are photographed with batteries of
35 mm cameras equipped with F/2, 
standard optics
(e.g. Bone 1993).
In front of the camera lens is a rotating shutter which interrupts
the image 25 times per second.
At least two camera batteries at locations 
apart are operated simultaneously. Every meteor photographed at
more than one site allows triangulation of the path of the meteor by
fitting planes through the meteor and the observing station.
The position of the meteor is found with reference to the altitude-azimuth
grid defined by the position of the stars at the beginning or end of the
exposure and the exposure times.
Once the trajectory has been determined,
the instantaneous velocity
follows from the number of the interruptions in the meteor path by the
rotating shutter and the known shutter frequency.
A fit to the changing velocity gives a measure of the
amount of deceleration in the atmosphere, from which the pre-entry
velocity (and its direction: the true terrestrial radiant)
is calculated. This velocity vector, in combination with the time of the
meteor, which is usually provided by a team of visual observers at each
site, determines the orbit in space.
The photographic systems can detect meteors of visual magnitude +0 and brighter
for fast meteors (angular speed 
)
or magnitude +1 and brighter for slow meteors (angular speed
). Exposure times are typically 15-30 minutes. The
photographic film is usually either Kodak Tri-X, TMAX 400, or Ilford HP5,
all nominally at 400 ASA but sometimes enhanced to about
1000 ASA by forced development. These emulsions are sensitive in the blue
and near-UV, where fast meteors have a rich emission line spectrum, while
at the same time they are relatively insensitive to diffuse background light.
The equipment
was built, manned and operated by amateur meteor observers of the Dutch
Meteor Society and some members of the Nederlandse Vereniging voor Weer
en Sterrenkunde - Werkgroep Meteoren.
The batteries are operated from various locations in the
Netherlands (
) and, on occasion,
in the Haute Provence (
), in the south of France.
As a rule, observing campaigns are organised
during moonless nights at the time of major stream activity. Hence,
most of the data have been obtained in the second and third weeks of April (Lyrids),
the month of July and the first two weeks of August (Delta-Aquarids and
Perseids), the end of October and beginning of November (Orionids and
Taurids) and the second week of December (Geminids).
One major shower, the Quadrantids, eluded observations as a result of
consistently
bad weather during the first week of January.
Outside of these periodic campaigns involving small-camera networks, seven all-sky cameras were operated routinely during moonless clear nights. Only meteors brighter than about magnitude -3 are recorded. Often, the time of the meteor is obtained by automatic light detecting systems that utilize a photo-multiplier tube, which are designed for the purpose by H. Mostert (1982). This network of all-sky cameras participates in the European Network (Ceplecha 1982), aimed at recovering meteorites and measuring their orbit in space. Indeed, a few possible meteorite falls were photographed (e.g. Betlem 1989; Betlem 1993), but no fragements have been recovered. Only one meteorite is known to have fallen in the Netherlands during the 12 years of operation. That meteorite fell in the town of Glanerbrug on April 7, 1990, in evening twilight at a time when it was still too light for meteor photography. We were able to derive an approximate orbit only from 200 eye-withness accounts (Jenniskens et al. 1992; 1992a).