Individual pixels in CCD cameras record only light and dark, black and white. They
don’t see color. To produce a color image requires taking three separate monochrome
(black and white) images though individual red, green, and blue filters. These three
black and white images, each representing a single color of light (red, green, or
blue), are then combined in your computer to produce the final full-color image.
Most CCD cameras take the three filtered images sequentially and store them in the
computer for later processing, with the operator changing color filters between
each exposure. However, several CCD manufacturers offer single-shot color cameras
that record all three color images at the same time, in a single exposure. These
cameras are also available in conventional monochrome versions. The single-shot
color CCD cameras are essentially identical to their monochrome counterparts with
the exception of the addition of a permanent color filter matrix over the pixels
that lets them take all three color images simultaneously, as explained below.
The images in the box above show the basic structure of the pixels on a Kodak CCD
detector, such as used on high-end SBIG and Finger Lakes Instrumentation single-shot
color cameras. The top row shows a monochrome detector, the bottom row shows a single-shot
color detector. The center image in each row is an actual photograph of the surface
of the CCD showing a small section of the pixel array. The drawings at the right
depict a side view of an individual pixel.
As you can see from the bottom row of images, the CCD structure for the single-shot
color version is the same as the monochrome version except for the red, green, and
blue pattern of filters over the pixels. The arrangement of colored filters over
the pixels in a single-shot color camera is a repeating square of RGGB known as
a Bayer pattern. This repeating pattern of RGGB pixels allows the separate red,
green and blue data to be collected in a single monochrome exposure and electronically
separated into the three monochrome images your computer needs to reconstruct a
full-color image. Every fourth pixel sees red, every fourth pixel sees blue and
every other pixel sees green. Special software extrapolates the RGB color data for
each individual pixel in the frame from the color information in the adjacent colored
Many of the more economical cameras from Celestron, Meade, and Orion use Sony CCD
detectors primarily designed for general use in camcorders and other consumer electronics,
rather than the more-specialized detectors from Kodak. The Sony detectors use a
color filter matrix of yellow, cyan, magenta, and green filters in a repeating sequence
to generate the full color spectrum using sophisticated addition and subtraction
algorithms to generate the desired RBG signal. The Sony filter matrix pattern is
What are the differences between taking three separate exposures versus one? Primarily
it is a trade-off between greater complexity, sensitivity, and flexibility at a
higher cost for the monochrome camera versus the single-shot color camera’s simplicity,
ease of use, and lower overall cost for color imaging. A single-shot color camera
needs only one image to do the job of the three needed by a monochrome camera/color
filter wheel system. While this is simpler and less time-consuming, it results in
a difference in the amount and quality of data recorded by each camera. The final
image from a single-shot color camera has the same number of total pixels as a color
image created by a monochrome camera and external filters, but it is created from
less original data than the three discrete images of a monochrome camera. In addition,
only one-third of the color information for each pixel is unique to that pixel and
measured directly. The other two color values are approximations, derived from adjacent
In the case of a monochrome camera, the external color filters can be designed specifically
for astronomical use, with high light transmission, precisely tailored response
curves, and with better control of the color balance between the emission line and
continuum light for different deep space objects. There is no way to tailor the
sensitivity and spectral response of each color filter in the matrix to match the
emissions of the object you are imaging, or to use special purpose narrowband filters,
such as Oxygen III, SII ionized sulfur, H-alpha, etc. The matrix filters are general
purpose red, green, and blue filters only.
As far as sensitivity is concerned, the monochrome camera is somewhat more sensitive
due mainly to the nature of the external filters compared to the micro-filters placed
over each pixel in the single-shot color camera. The monochrome camera requires
more work to take a tri-color image, however, and the addition of the required filters
and color filter wheel makes it more expensive.
The effective QE (quantum efficiency) of the monochrome camera with external filters
is slightly higher than the single-shot color camera based on the filter transmission
characteristics. But remember, the monochrome camera must take three frames versus
the single-shot color camera's single frame. So for a proper comparison, a monochrome
camera taking a 20 minute image through each of the three filters should be compared
to a single-shot color camera taking a single 60 minute image. In this case, the
single-shot color camera compares very well to its monochrome counterpart. Moreover,
self-guiding the single-shot color camera is easier due to the fact that the separate
built-in guider detector is never covered by a filter which can affect the tracking
performance of the guider. Where a monochrome camera shines is in taking a grayscale
image, or in taking narrow band monochrome or tri-color images of emission line
objects. But for simple color images, single-shot color cameras are very capable.
order to increase the light-gathering efficiency of a CCD camera, some CCD detectors
use a microlens array over the imaging detector to gather and focus more of the
incoming light onto the individual pixels.
Each photosite (picture element or “pixel”) is surrounded by an opaque mask covering
the shift registers and circuitry necessary to read out the image signal gathered
by the camera. This means that some of the light falling on the detector lands on
the detector’s mechanical structure rather than the light-gathering portion and
is lost. This is shown by the green arrows in the illustration.
The microlens system is an array of tiny clear plastic lenses placed over the CCD
detector so that a single miniature lens is situated over each pixel. These lenses
bend the incoming light rays so that the light that would normally be lost on the
CCD structure is directed instead towards the photosite, where it is recorded as
part of the image. These deflected rays are shown by the red lines in the illustration.
The microlens system markedly improves the light gathering efficiency of each pixel
by putting to use incoming light that would otherwise be wasted.
The Celestron Nightscape CCD camera combines the simplicity of a one-shot color imaging camera with the sophisticated features and software of more expensive astronomical imaging systems. It uses a Kodak 10.7 megapixel color sensor and regulated thermoelectric cooling to give you instant results in just a single exposure. Coupled with the internal mechanical shutter and Celestron AstroFX control software, you can also automatically combine multiple images and dark frames to create images comparable to those taken with professional grade cameras costing thousands more.
A review in Astronomy magazine said, "Without a doubt, the Celestron NightScape CCD is one of the simplest cameras we have used. The control software is straightforward and easy to operate, and both it and the camera performed without a hitch. If you are looking for a one-shot color CCD camera that offers high-quality features and simplicity without having to sell the farm, this camera will not disappoint you."
With compact 4.75 micron x 4.75 micron pixels and 2x2 and 4x4 binning, the Celestron Nightscape is capable of providing optimal resolution with a wide variety of telescope types and focal ratios. With an f/10 system and 2x2 binning, for example, Nightscape gives you a large image scale while still providing sub-arc second image sampling. This is ideal for bringing out fine detail in planets and compact deep-sky objects. Or you can take advantage of the high resolution 4.75 micron x 4.75 micron pixels with a Celestron EdgeHD system working at f/2 to capture your favorite wide field deep space objects while maintaining a resolution that’s better than your "seeing" conditions. Nightscape gives you the versatility to match all the configurations of your optical system.
The Celestron NightScape uses Kodak's KAI-10100 color imaging sensor. This 10.7 megapixel single-shot color CCD lets you take full-color CCD images with only a single exposure. There is no need for the three or more separate exposures through different color filters needed for tri-color imaging with a conventional monochrome camera. For more details, click on the “Single-Shot” icon above.
This CCD sensor has an array of 3760 x 2840 pixels, each measuring 4.75 microns square. The imaging area is approximately 17.9 x 13.5mm and has a diagonal measurement of about 22.5 millimeters (a Four Thirds format chip). With its relatively small pixels and large image area, the NightScape is ideal for wide field imaging with short focal length/fast focal ratio optics in its high resolution (unbinned) mode.
Binned 2x2 the pixels are 9.5 microns square, with a 2.67 megapixel array. Binned 4x4 they are 19 microns square, with a 668,750 pixel array. This feature makes it possible to match the camera’s pixel size to your seeing conditions and telescope, from a small refractor up to a large SCT.
The Kodak CCD in the Celestron NightScape has >100x antiblooming provided by a vertical overflow drain for each pixel. It also has microlens technology to improve the effective Quantum Efficiency of the sensor, allowing it to be used in a wide variety of optical configurations. For more details, click on the “Microlens” icon above. Quantum efficiency is 32% at 630 nm (red); 42% at 550 nm (green); and 40% at 470 nm (blue). There are IR cutoff and anti-reflection multicoatings on the high transmission Schott B270 glass optical window over the Kodak sensor.
The Celestron NightScape has a 2” nosepiece for connection to your telescope. The nosepiece can be unthreaded to reveal standard female T-threads in the front plate of the camera body for connection to off-axis guiders or T-mount camera adapters. The spacing from the front plate to the sensor is the same distance as most DSLR cameras, allowing compatibility with most standard DSLR T-adapters.
The 4” diameter Celestron NightScape body is circular in cross section. Unlike ordinary rectangular camera bodies whose corners can project into the light path when used in a Fastar/Hyperstar configuration with Celestron catadioptrics, the round NightScape body will not produce unnatural diffraction artifacts in your images when mounted in the center of the corrector.
A built-in mechanical shutter is included for easy acquisition of dark frames.
The NightScape has a fast USB 2.0 interface to your computer, with a 10’ USB cable supplied as standard equipment. It needs a Pentium™ or equivalent (or higher) PC to operate. The PC should be running Windows XP™, Windows Vista™, or Windows 7™ (or higher), in 32-bit or 64-bit mode. The PC needs a minimum of 1 GB RAM, with 20 MB of disc space for program installation, and a 1024 x 768 pixel 16-bit color or higher video display minimum,.
The NightScape has single stage regulated thermoelectric cooling (TEC). A variable fan control provides a vibration free laminar air flow to dramatically reduce the thermal noise inherent in all imaging sensors. The TEC will cool the NightScape to 20° C below ambient.
The supplied Celestron AstroFX software takes you step-by-step from taking images to processing the final result. AstroFX gives you full control of your camera, including temperature regulation, exposure control, and computer assisted focusing for easy image acquisition. AstroFX knows just what to do with your images and calibration frames once you’ve taken them. It will help you create a final master image that's been stacked, stretched, sharpened, saturated, and ready to share with your friends in a snap. The Celestron NightScape is also compatible with MaxIm DL and ASCOM drivers.
Detector specifications are as follows:
Detector: Kodak KAI-10100 single-shot color with microlens.
Pixel Array: 3760 x 2840 pixels.
Pixel Size: 4.75 x 4.75 microns.
Total Pixels: 10,678,400 (10.7 megapixels).
Full Well Capacity: ~25,000e-.
Dark Current: ~2e-/pixel/second at 0 degrees C.
Readout specifications are as follows:
Exposure: 0.001 second to 24 hours (2x2, 4x4 binning); 0.01 second to 24 hours (unbinned).
A/D conversion: 16 bits.
Read noise: ~13e- RMS.
Binning modes: 1x1, 2x2, 4x4.
Full frame download: 20 seconds or less for full frame image.
Sub-Framing: full, half, quarter, selectable.
Optical specifications with a 4” f/6 (610mm focal length) refractor, unbinned, are as follows:
Field of view: 73.76 x 97.66 arc minutes, at 1.56 arc seconds/pixel.
System specifications are as follows:
Standard cooling: single stage thermoelectric, active fan, -20° C from ambient maximum, air cooling only.
Usable temperature range: 40° to -40° C (104° to -40° F).
Power requirements: 12VDC at 2.5 amps, tip positive.
Computer interface: USB 2.0.
Computer compatibility: Windows XP, Windows Vista, or Windows 7 (or higher), in 32-bit or 64-bit mode.
Optical head: 4” diameter/100mm; weighs approximately 2 pounds/0.9 Kg.
Supplied mounting methods: T-thread, 2” nosepiece.
Back focus needed: 2.16”/55mm with 2” nosepiece; 1.04”/26mm without nosepiece.