Webcams display a real-time image on a video camera, TV screen, etc.
These stream images at 30-60 frames per second. Most work only on the
brightest objects, like the Moon, Jupiter, Venus, Saturn. Some are sensitive
enough for the very brightest DSOs. Can be impressive and cheap.
Fast integration video cameras
These can have internal integration of images, can shoot up to 60 frames
per second or as slow as several seconds per shot. The images can be
fed to a screen device or laptop. Many times more sensitive to light
than webcams, and usually with larger chips. This is the “almost
real-time” revolution occurring in astronomy right now. Examples:
Imaging Source cameras, StellaCam, etc. They can be cooled for lower
noise. Color or monochrome.
These are low sensitivity but often high resolution cameras for planetary
imaging. Images have to be “integrated” or “stacked”
in a computer to see the best image before processing. Opticstar Lumenera
cameras can provide those “flyby” images you see on the
Deep Sky Imagers / CCD astro cameras
These have the highest sensitivities and can take the longest images.
Images have to be stacked in a computer to build composite shots. They
can be color, or monochrome. Monochrome versions are typically higher
sensitivity and are often used with LRGB or UVBRI filters depending
on object and camera. They are often/usually cooled for lower noise.
It is in these cameras that the chips can get really large and quite
expensive. Examples: Meade DSIs(all grades/levels), SBIG cameras, Apogee
cameras, Opticstar and FLI. The higher grades of these (SBIG up) can
have “regulated” cooling so they can be used for research.
Large objects do not require the smallest pixels. Smaller pixels yield
higher resolution, but more computer power is required to process the
images if the images themselves are larger.
Digital SLR cameras are often used by beginners to capture sky images.
Most can capture long images if some form of device is used to keep
the shutter open, but even then a lot of them limit maximum exposure
times to prevent damage to the chip. They are not capable of the highest
resolution because they shoot through a screen, but the on-board memories
can usually store several shots so the images can be downloaded and
stacked later. Taking shots this way usually requires “faith”
that the image is well-centered, since most DSOs are too faint to be
seen on a screen.
- ALT-AZ photography has to be limited to one minute or less to avoid
field rotation for stacked images. However, webcam and Fast integration
cameras aren’t limited that way because of the way they form images.
They can be used with any scope that can support the weight. More sensitive
cameras can also be used Alt-Az if many short images are stacked.
- Equatorial photography avoids field rotation and allows long timed
exposures of deep-sky objects that are quite faint. This includes fork-mounted
scopes on wedges as well as equatorial mounts.
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