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Why use a CCD video camera and not an SLR?
You can buy a modern SLR camera body such as the Canon EOS 1000D for little more than an integrating CCD video camera, and such cameras are often used for astrophotography. However, SLR cameras use high resolution colour CCDs, and this has two disadvantages for imaging faint objects.First, each pixel must be divided into three colours with filters, and this reduces the light input per pixel by more than a factor of 3. Second, high resolution in less expensive SLRs means small pixels, and light input is proportional to pixel area. Finally, modern SLR cameras automatically filter out CCD noise, which can also eliminate faint stars ! It is much better to capture the original image and eliminate noise using a computer, or better by cooling the CCD itself.
So to image faint objects you actually need a low resolution monochrome CCD with the largest possible area, not a high resolution colour camera. A colour SLR camera can easily be more than an order of magnitude less efficient, which means either counting much longer (with more accurate and expensive tracking mechanics), or buying a telescope with a more expensive larger aperture (light input is also proportional to the aperture area of the optics). SLR cameras are also relatively large and heavy, which may also require more expensive telescope mechanics.
A practical reason for using an integrating CCD video camera rather than an SLR is that then you can display
the output image in real time on any TV screen or monitor with composite video input (most modern TVs). Even though the
image is integrated over several seconds or minutes, it is output at normal TV scan frequencies.
Wat-120N highly sensitive integrating camera
The Wat-120N monochrome camera is the
amateur astronomer's choice for deep sky imaging on a budget.
It combines a very sensitive Sony CCD with on-board integration over exposures of up to 10 seconds
in a light-weight, compact body that can be readily adapted to any telescope. Since sensitivity is proportional to pixel size,
the Wat-120N (Stellacam-II) uses a large 1/2" CCD with a limited number of pixels (752x582). Impress your friends
with stunning images of the stars displayed on your TV or computer, such as
these examples.
Wat-120N+ super sensitive integrating camera
The Wat-120N+ is an advanced version of the Wat-120N that allows unlimited exposures as well as very
short exposures for brighter objects. Again sensitivity is maximised by the choice of a large 1/2" CCD, in this case
the new Sony ICX419ALL.
Cameras with smaller CCDs or higher resolution, especially colour cameras, cannot match this sensitivity,
far superior to that of the human eye.
An optional Peltier cooler is available to largely eliminate electronic noise
for long exposures. Here are
more examples that show how such cameras can be used for deep sky viewing even in urban environments.
Wat-902H2 meteor & planetary imaging camera
The Wat-902H2 Ultimate
is even more sensitive for fast exposures, but the image is real-time with no integration. This makes it
ideal for transient events such as meteor and satellite imaging, or observation of brighter planetary
objects. Integration is still possible on a computer, using image-stacking software. Slightly less sensitive
versions such as the Wat-902H2 Supreme
and the inexpensive Wat-902B are
available with either 1/2" or 1/3" sensors. Here is a
comparison of the Wat-902H2 and the Wat-120N for meteor tracking.
Wat-231S2 high sensitivity colour CCD camera
The Wat-231S2
is the latest ultra-high sensitivity colour camera from Watec. (Colour cameras are
less sensitive than black and white cameras, because the three colour pixels necessarily share the same area of the CCD).
The following parameters can be set manually on the camera housing: automatic gain control (AGC) and electronic iris,
shutter between 1/50 to 1/10,000 sec, gain from 6 to 32dB and colour temperature.
The back focus of the lens unit can be adjusted exactly by a fine thread on the lens mount ring.
All other Watec products can be provided to order,
at the lowest prices available in Europe,
such as the new Wat-1000,
a colour "day and night" camera than can be switched to the more sensitive black and white mode when required.
Extension cables & 12v stabilized power supply
All cameras require a stabilised 12v power supply, which can be provided as an optional extra.
We can offer 10m extensions for both the video and Wat-120N/N+ controller cables. These extensions can be chained to produce 20m or more lengths.
Even longer distances can be obtained with the wired or wireless remote control
and wireless video transmitters.
USB-2 Computer Interface and free software
Output from these CCD cameras can be displayed on a TV or monitor using a simple composite video cable,
but a USB-2 computer interface is essential for connecting them to a computer. We propose an inexpensive
USB-2 frame-grabber and software.
If you use cameras to monitor several locations, we can supply a 4-channel grabber
or a 4-channel recording grabber with multi-channel software.
Philips 7" TFT video monitor
Instead of a computer, you can use any TV screen with composite video input.
We can supply the
Philips 7" TFT video monitor, by far the best we have tested -
strong, and beautifully made, with a standard 100V-240V/12V transformer (supplied).
Just plug in the video and power cables to see the camera image integrated over exposure time.
A simple video splitter can be used to take the same image to your computer.
(US and EU compatible, click photos to enlarge)
Peltier Cooling Option
CCDs when warm generate electronic noise called "dark current" which shows up with long exposures
as bright pixels.
The left image above shows such "hot pixels" with a long high-gain dark-field exposure from an unmodified camera;
the right image, from a camera cooled by -25C using a Peltier cooler, heat-sink and fan,
shows few hot pixels.
We offer a Peltier Cooling option that can be retro-fitted (US & EU compatible).
The photo on the left shows the cooler on a Wat-120N+ together with an optional wireless exposure controller
(on top with the red LED light).
Wired Remote Control
The Wat-120N/N+ camera comes with its own 16-pin wired controller on a 3m cable, which can be used with 10m extensions.
Much longer distances (40m or more) can be obtained with the optional "wired" controller, which uses ordinary 2-wire telephone cable. This is also an advantage if the controller cable must exit an instrument tank, or if the similar wireless remote control (below) cannot be used.
A 30g wired receiver is plugged into the camera in place of the existing controller, which is then replaced by the alternative hand-held remote controller (left). Exposures of 0.0005 secs to 90 mins can be set, and once set the remote controller, which runs on batteries, can be switched off; the previous settings will then be used whenever the camera is powered on (US & EU compatible).
This optional "wired" controller, as well as the similar "wireless" controller (below), include an RS232 port and cable to
allow them to be controlled by a computer using simple batch files or the MS-Windows hyper-terminal software. This is described
in the wired/wireless controller manual.
Wireless Remote Control
This is a modification of the optional wired controller, to provide completely wireless operation. A 30g 1mW receiver
is plugged into the camera in place of the existing controller, which is replaced by a hand-held remote transmitter (left).
Exposures of 0.0005 secs to 90 mins can be set, and once set the remote transmitter, which runs
on batteries, can be switched off; the previous settings will then be used whenever the camera is powered on (US & EU compatible).
For details, see the wired/wireless controller manual.
Wireless Video Transmitter
A wireless video transmitter
with its associated receiver, both about the size of a large cigarette packet, can be supplied to
transmit the camera image over distances of up to 40m. A choice of 4 channels in the 2.4GHz band can be selected.
(European specific with 2x 230VAC-9VDC transformers included).
What telescope to use with a Watec camera ?
The efficiency of a telescope is proportional to the area of its aperture, just as the efficiency of a CCD is proportional to its area. But for integrating cameras such as the Wat-120N it is more important to have a stable mount that can track objects precisely for at least some seconds. Larger telescopes are also more difficult to transport and setup, take longer to reach a stable temperature, and require more solid mounts. Watec cameras are so light they can be used with even the smallest telescopes and mounts.Many of the most beautiful objects in the sky are actually quite large, but faint; the milky way is the best known example. For these objects you don't need high magnification, but rather a wide field of view. A good choice for a beginner might then be a short-focal refractor such as the SkyWatcher 80/400mm or better the ED-80 version on an equatorial mount and motor to compensate for the rotation of the earth during longer exposures, such as the SkyWatcher EQ-3-2 or EQ-5. If later you buy a larger telescope, the SkyWatcher (also called Orion & made in China by Synta Optics, who now own Celestron) remains a good choice as a guide scope on more expensive instruments.
Even when you upgrade, you may still want an instrument you can use in your backyard, and suburban light pollution will anyway limit the size of telescope you can use. You can reduce light pollution by adding a simple filter in front of your camera. A H-alpha filter will only pass a narrow range of hydrogen wavelengths emitted by nebulae. Since sensitive monochrome cameras are normally used for astro-imaging, you will also need RGB colour filters if you want to reconstruct a colour image.
There are beginner's guides
to buying a telescope,
and also telescope comparisons, but
modern computerised instruments like the
Celestron CAM GoTo with its robust equatorial mount are a good choice for more serious astro-imaging.
The Schmidt-Cassegrain web site is a fine source of information
about such compact telescopes. Watec cameras are so small that you can eventually fix one in front of an SCT to convert it
to a dedicated wide-field Schmidt camera with the
Celestron Fastar
or Starizona Hyperstar attachments.