Star Ware: The Amateur Astronomer's Guide to Choosing, Buying ...

248 Star Ware
most important requirement of the astrophotographer, followed closely by the
right equipment. It’s tough to bottle the former for sale, but there are lots of
companies looking to sell you the latter!
Cameras
While successful astrophotographs can be taken with many different types of
cameras, most amateurs prefer the 35-mm single-lens reflex (SLR) camera.
Single-lens reflexes allow the photographer to look directly through the lens of
the camera itself, a critical feature for aligning the image, especially when photographing
through a telescope (with most other cameras, the photographer is
viewing through a separate viewfinder). SLRs also offer the maximum flexibility
in terms of film and lens availability, both discussed later in this chapter.
Not all 35-mm SLRs are suitable. For astrophotography, a camera must
have a removable lens with manually adjustable focus, provisions for attaching
a cable release to the camera and the camera to a tripod, a manually set,
mechanical shutter with a “B” (bulb) setting, mirror lockup, and interchangeable
focusing screens. Unfortunately, few of today’s 35-mm SLRs fit this bill. In
an attempt to attract more weekend photographers, most camera manufacturers
offer cameras with automatic everything, from focus to exposure to flash
control. All of these are nice for taking pictures of the family picnic, but are of
no use to astrophotographers. Quite to the contrary, the long exposures
required for astrophotos (usually measured in minutes, even hours) will
quickly drain the power from expensive camera batteries. When that happens,
the camera shuts down and becomes useless until a fresh set of batteries is
inserted.
Which cameras are best for astrophotography? Table 7.12 lists several
excellent alternatives, from both the past and the present.
Expensive does not necessarily mean better for astrophotography. All of
these cameras will work well for wide-field constellation shots as well as
through-the-telescope photos of the Moon and the Sun, but their differences
will become more apparent when taking long-exposure telescopic shots. Here,
the benefit of interchangeable focusing screens and mirror lockup will become
apparent. Most subjects photographed through telescopes are very faint, making
it difficult to line up and focus the shot when viewing through most standard
focusing screens. A simple ground-glass screen will provide the brightest
possible images, a great aid in focusing and composing (see further discussion
under “Focusing Aids” later in this chapter). Mirror lockup is recommended
for reducing mirror slap, which occurs every time the shutter is tripped and the
camera mirror pivots out of the way. Swinging the mirror out of the way before
the shutter is opened eliminates most vibration, reducing the chances for
blurred images.
Lenses
Just as all cameras are not suitable for photographing the sky, neither are all
lenses. But before an educated choice can be made, the photographer must