Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A collimated beam projector for precise telescope calibration   The precise determination of the instrumental response function versus
wavelength is a central ingredient in contemporary photometric calibration
strategies. This typically entails propagating narrowband illumination through
the system pupil, and comparing the detected photon rate across the focal plane
to the amount of incident light as measured by a calibrated photodiode.
However, stray light effects and reflections/ghosting (especially on the edges
of filter passbands) in the optical train constitute a major source of
systematic uncertainty when using a flat-field screen as the illumination
source. A collimated beam projector that projects a mask onto the focal plane
of the instrument can distinguish focusing light paths from stray and scattered
light, allowing for a precise determination of instrumental throughput. This
paper describes the conceptual design of such a system, outlines its merits,
and presents results from a prototype system used with the Dark Energy Camera
wide field imager on the 4-meter Blanco telescope. A calibration scheme that
blends results from flat-field images with collimated beam projector data to
obtain the equivalent of an illumination correction at high spectral and
angular resolution is also presented. In addition to providing a precise system
throughput calibration, by monitoring the evolution of the intensity and
behaviour of the ghosts in the optical system, the collimated beam projector
can be used to track the evolution of the filter transmission properties and
various anti-reflective coatings in the optical system.

22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
34
The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
11
The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex
0
The categories of this paper are: hep-ph
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph
13
The categories of this paper are: quant-ph
17
The categories of this paper are: q-fin
2
The categories of this paper are: math