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I. The Nikon D100 Digital
Single Lens Reflex (DSLR) Camera
The D100 digital single lens
reflex camera (DSLR, or digital SLR) was introduced by Nikon on
February 21, 2002 (Nikon, 2002). It is a compact single lens
reflex digital camera designed to resemble the body of a regular
Nikon SLR film camera. No lenses are supplied with the camera.
It will use any lens with standard Nikon mounts and is fitted
with a standard cable shutter-release button. The D100 contains
a 6.1 megapixel high definition 3008 x 2000 pixel 23.7 x 15.6 mm
RGB CCD chip. Each pixel is approximately 8 microns in size.
Even though the CCD chip in the camera is large by amateur
astronomy standards, it is smaller than an equivalent 35 mm film
frame, and the focal length of any lens attached to the camera
is increased by a factor of 1.5. Thus, a 20 mm focal length
lens attached to the D100 has a magnification and field of view
equivalent to that of a 30 mm focal length lens. The chip is
overlaid with a grid of color filters, and it conveniently
produces color images in a single shot.
Simple digital cameras have
been on the market for many years, and they have gained much
popularity due to their easy use, excellent results, and simple
operation without the necessity to purchase film or have film
developed. Digital SLR cameras are a further extension of the
simpler digital cameras that have been marketed by many
manufacturers, including Nikon, Canon, Olympus, Fuji, Pentax,
Sigma, Sony, Minolta, Kodak, and others.
Single lens reflex cameras use
an internal flip mirror to enable the photographer to view and
focus on the desired scene through the same lens used to take
the photograph or digital image. SLR film cameras are giving
way to DSLR cameras, because the chips in the digital cameras
are considerably more sensitive to light, and they produce
digital files instead of slides or prints. These files allow
easy computer processing and enhancement.
The D100 contains a multitude
of features for the advanced photographer. Most of these
features apply to high light level imaging, such as outdoor
daylight photography or indoor flashbulb photography. Many of
these features will be of no interest for an amateur astronomer
using this camera for astrophotography. Of special interest for
the astrophotographer is the wide range of exposures and ISO
values available with the camera. Its exposures range from
1/4000 sec to 1, 2, …10, 20, 30 seconds, and bulb. Its ISO
values can be set from ISO 200 to ISO 6400. It supports a
number of file format types including uncompressed TIFF,
compressed JPEG, and uncompressed RAW files.
The Nikon D100 camera used in
this project was purchased in late 2002 and contains a 512 MB
CompactFlash (CF) Card for image storage. A second battery was
purchased for the camera so that a fresh battery power would
always available. The D100 uses a rechargeable Li-ion Battery
Pack (7.2V DC) that will give hundreds of exposures under normal
daylight working conditions and temperatures. Because much
astrophotography is performed at night in cold conditions, the
battery may not last an entire evening and has to be replaced
after 4-6 hours of continuous use. Fortunately, it can be
recharged in only 2 hours. For processing, the camera image
data are easily downloaded to a computer via a supplied USB 1.1
compatible connector.
I own two observatories. The
3towers Observatory is my home observatory located on the North
side of Tucson, Arizona. My other observatory, the Grasslands
Observatory, is located at a very dark site 60 miles Southeast
of Tucson. It contains a 24-inch f/5 reflector. The Nikon D100
camera images shown in the figures for this essay were mainly
obtained at my home in Tucson or at the Grasslands Observatory.
For maximum functionality, a
high quality SLR digital camera should be purchased with a
backup battery pack and as large an image storage chip as
possible. In the case of the Nikon D100, this was all purchased
for ~ US $2000. These cameras are very popular with advanced
amateur photographers and with professional photographers.
While they are quite expensive, they are very versatile, and
their price is dropping. Most of the conclusions reached about
the Nikon D100 herein are applicable to more modern digital SLR
cameras. |
