|The QuickCam uses a Charge Coupled Device (CCD) to capture an image. The image is
accumulated and then transmitted through a parallel port to a computer. Software then
converts the bits into images. For use with a telescope, the camera was disassembled, the
lenses and filters were removed, and the CCD and supporting electronics were housed in a
plastic electronics project box. A PVC pipe fitting was modified to attach the project box
to the telescope focuser. The camera was mounted at the telescope's prime focus (or more
technically 'Newtonian focus'), which means that the sensor was located at the focal point
of the telescope's primary mirror (below). - More Detail -
What can be seen with a CCD and a telescope is a function of the sensor size, sensor construction, and the telescope's focal length. Relevant sensor data and calculations used to determine the imaging characteristics of the QuickCam/telescope combination are summarized in the following table for the Greyscale Quickcam.
The following formula can be used to determine sky coverage per pixel for a given camera pixel size and telescope focal length:
P = sky coverage per pixel (arc-seconds/pixel)
The image width or height can be determined by:
I = image width or height (arc-minutes)
The moon covers about 0.5 degrees (30 arc-minutes) of the sky. Therefore, a minimum of 12 separate 10.2 arc-minute x 7.6 arc-minute images will capture the entire Moon, as shown below.
The diameter of the moon is 3,476 km (2,160 mi). For regions that are not too foreshortened by the curvature of the Moon's surface (like Sections 5 and 8 above), each pixel covers an area of about 3.7 km x 3.7 km (2.3 mi x 2.3 mi). The image covers an area about 1,175 km x 880 km (730 mi x 550 mi) for these regions. Depending on physical characteristics and lighting, the smallest features visible are on the order of 15 km (10 mi). With a detailed Moon atlas, features half that size can be identified. For comparison, the best available technology can view features about the size of a football stadium.
The angular size of an object viewed at a distance can be determined by:
A = 206,265 d / r
A = angular size of object, arc-seconds
The angular size of Jupiter in June 1998, for example, was about 40
arc-seconds (based on a diameter of 142,980 km and a distance of 7.28 x 108
km). With a resolution of 1.9 arc-seconds/pixel for the telescope/QuickCam combination,
the diameter of Jupiter is about 21 pixels across. This corresponds to a resolution of
about 6,800 km/pixel (4,200 mi/pixel). By comparison, the resolution of the Moon is about
3.7 km/pixel (2.3 mi/pixel). The attempts I have made so far have not resulted in any
satisfactory images, but with patience and skill it might be possible to record some
interesting images. The figure below illustrates the maximum size of Saturn, Mars, Jupiter
and the Moon (when each is closest to Earth) in the QuickCam's 320 pixel x 240 pixel
The standard QuickCam software (Version 2.1) was used to create the images - it was more or less 'point and shoot'. An image editing program was used to create the two-image mosaic and to convert the QuickCams's bitmap files to JPEG files.
The sensor is only applicable for lunar or planetary imaging that use exposures on the order of a few seconds or less. Longer exposures necessary for deep-sky imaging are not possible with this device. Longer exposures require that the sensor be cooled to minimize signal noise (as is done with cameras intended for astronomical work). Some have retrofitted the QuickCam with a cooler, with mixed success. But this defeats the primary objective of this particular effort, which is to do as much as possible with as little as possible.
The inspiration for trying this out was John Buchanan's article "QuickCam Astronomy," Sky & Telescope, June 1998. Check out his site for information on camera modifications, samples of his lunar and planetary images, and links to other sites.
António Cidadăo's Home-Page of LUNAR and PLANETARY Observation and CCD imaging provided inspiration for future projects with the camera. His site includes descriptions of his QuickCam modifications, imaging techniques, and several interesting projects.
Modification of the QuickCam is not approved by the manufacturer and will void its warranty. The camera was designed to be opened by the manufacturers technical service only. If you open your camera, it's at your own risk.