Specifications

92 AUTOSTAR CCD PHOTOMETRY
(2) "Tee Shirt" Flats – A variant technique employing a white
cloth stretched over the front of the telescope, to diffuse the light
source. As with dome flats, the light source must not be allowed to
shine directly into the telescope. A second stretched cloth diffuser
might also be placed over the light source. One advantage is the
method may be used during daytime, provided that no light is
allowed directly into the optical train.
(1) Light Box Flats – This is probably the best and most
consistent method. A lightweight box or enclosure is fabricated
and placed over the entrance to the telescope optics. The box
typically contains one or more diffuser sheets, and small lamps or
light–emitting diodes (LEDs) which are arranged to shine upward
onto the inside of the box, which is constructed of white diffusing
material. If used outdoors with other observers and telescopes in
the vicinity, the box should be sealed against possible light leaks.
Light Box Construction Notes
At HPO, we researched a dozen or more web pages detailing
construction of light boxes, including several offering commercial
products for sale. The consensus on size, construction materials,
and suggested light sources was as follows:
Box Size – Up to about a 12 inch (30 cm) telescope aperture, the
preferred box size was approximately 14 inches (35.6 cm) square,
with the length about the same or a little shorter. In other words, a
cube. a little larger than the maximum telescope tube end size (or
corrector cell OD on SCTs). The box size could be reduced for
telescopes 8 inches (20cm) or smaller, and an even smaller size
could be made for telephoto lenses.
Construction Material – The preferred material seems to be
“Foamcore” sheeting, which is a styrene plastic foam sheet (the
core) covered in white matte paper. It is stiff and lightweight,
typically 1/4 inch (6 mm) thick, and readily available in 30 x 40
inch (.75 x 1 m) (and larger) sheets in arts and craft supply stores.
It is inexpensive, easily cut to size, and also comes in black.