The two cameras to be compared are the TRUST WB-5400 megapixel webcam that I obtained early 2007 and the TRUST Spotlight Pro webcam that arrived today.
I have chosen these two cameras because they are from the same manufacturer and both have hardware resolutions of 1280 x 1024, which is a very suitable resolution for Lunar and solar imaging, consistent with reasonable frame rates. Back in 2007 I produced very satisfactory lunar images with the WB 5400 as can be seen on the
QCUIAG website in the megapixel imaging section. I also published an article in Astronomy Now the following year:
The high resolution webcam revolution: A new generation of megapixel webcams is producing high-resolution astronomical images from CMOS chips. S.J. Wainwright 2008, Astronomy Now, 3, 80-81.
The WB-5400 is no longer available new but at the time of writing, the Spotlight Pro is available at about a £13 - £18 price point in outlets such as Amazon UK and Currys PC World.
Both cameras have CMOS sensors with native hardware resolutions of 1280 x 1024.
In addition, a telescope (Mogg) adapter can be obtained from Amazon UK for £4 - £8.
Preparing the cameras for astronomical imaging
Both are easy to modify. The cases are easy to open and the lenses are standard M12 threaded, which screw right out. The Spotlight Pro has six LEDs which were removed by clipping their long legs. This removes an unwanted component and creates six ventilation holes that do not allow dust access to the sensor.
A standard Mogg telescope adapter can be screwed into the lens threads and the camera is ready for imaging.
Spotlight Pro
WB-5400
The following tests were done using a Skymax 127 Maksutov and an 80% waxing, gibbous Moon.
The tests involved:
a) Imaging the Moon with the same telescope and different cameras.
b) Looking for evidence of vignetting.
c) Looking for evidence of compression artefacts.
d) Considering the quality of the images obtained
AstroDMx Capture for Linux was used with both cameras and
AstroVideo for Windows was also used with the the WB-5400, which was never made fully compatible with Linux.
The WB-5400 has a WDM Windows driver that provides even more controls than the new Spotlight Pro.) AVIs were captured by both systems and also, the WB-5400 was tested with its minimal controls in Linux).
However, the plot thickens: I have two TRUST WB-5400 cameras dating back to 2007. On probing the kernel modules, the two (apparently identical) cameras have two different sensors. One is a Micron MT9M111 sensor and the other contains a Silicon Optronics SOI968 sensor. They are both 1.3 M pixel CMOS sensors and are controlled
fully by the WDM driver.
With a standard Linux kernel, the camera with the Silicon Optronics sensor offers a working gain control in AstroDMx Capture for Linux whereas the camera with the Micron sensor does not offer gain control. Both cameras offer a working gamma control, but the Brightness and contrast controls do not work.
AstroVideo is Windows capture software that I worked on with Bev Ewen-Smith of
COAA at the turn of the century. Bev did all of the coding and I did testing and debugging as well as specifications.
AstroVideo was initially developed for off-chip video integration by summing hundreds and thousands of video frames from low-light surveillance cameras into 32 bit Fits files. The software utilises track and stack of the movement of objects on the sensor and actually synthesises long exposures by summing many short exposures. Some of the results obtained can be seen on the
QCUIAG website. If you use Windows and wish to use legacy cameras or video cameras via capture cards, then AstroVideo is the Windows software to use. In these experiments, we used AstroVideo to control the TRUST WB-5400 camera, and to capture AVIs from it with full controls.
The problem with using modern CMOS webcams for Lunar and planetary imaging are mainly threefold:
1) Many small, HD CMOS sensors are intended to work with small lenses very close to the chip and they display various degrees of pixel vignetting, that must be corrected by flat fielding.
TRUST-WB5400 with and without flatfield, captured with AstroDMx Capture for Linux
No evidence of vignetting with this 2007 camera
TRUST Spotlight Pro with and without flatfield, captured with AstroDMx Capture for Linux
Vignetting, corrected with flatfield
2) Many CMOS webcams compress the video stream and give no options for uncompressed or lossless compressed video streams. I suppose that this is OK for video conferencing in HD, but is absolutely useless for imaging the Moon etc, where compression artefacts render the resulting image useless.
Screenshot of AstroDMx Capture for Linux capturing data from the TRUST Spotlight Pro
Screenshot of AstroDMx Capture for Linux capturing data from the TRUST Spotlight Pro
TRUST Spotlight Pro
Clavius Region
Screenshot of AstroDMx Capture for Linux capturing data from the TRUST Spotlight Pro
TRUST Spotlight Pro
Sinus Iridum region
Very little compression was evident in the Spotlight Pro, with virtually none in the WB-5400.
TRUST-WB5400
Clavius region captured with AstroDMx Capture for Linux with minimal controls
TRUST-WB5400
Clavius region captured with AstroVideo for Windows with full controls
3) Many CMOS webcams offer very little control over the video stream, which means that notwithstanding points 1 and 2 above, it is difficult, or impossible, to achieve satisfactory exposure across the whole image.
AstroVideo screenshot showing the controls of the WB-5400
The conclusion drawn is that whilst both cameras produced acceptable images, the old WB-5400 was superior on two counts:
- The WB-5400 displayed no pixel vignetting.
- The WB-5400 displayed no noticeable compression.
Modern webcams almost invariably use compression to speed up the video for video conferencing. They also use small sensors, which are subject to pixel vignetting. Both of these facts are unfortunate for the use of these devices for astronomical imaging.
As devices for outreach, or as an introduction to lunar and planetary imaging, cameras such as the modern TRUST Spotlight Pro are quite suitable.
