Camera Sensors
As light passes through a telescope optical tube assembly, it focuses on the camera’s image sensor. An image sensor is made up of many photodiodes and each photodiode corresponds to a picture element, known as “pixel”, on an image sensor. Each pixel on an image sensor registers the amount of light it is exposed to and converts it into a corresponding number of electrons. The brighter the light, the more electrons are generated.
When building a camera, there are two main technologies that can be used for the camera’s image sensor:
- CCD (charged-coupled device
- CMOS (complementary metal-oxide semiconductor)
- MegapixelSensors
When building a camera, there are two main technologies that can be used for the camera’s image sensor:
- CCD (charged-coupled device
- CMOS (complementary metal-oxide semiconductor)
- MegapixelSensors
CCD Technology
CCD sensors have been used in cameras for over 30 years and present many advantageous qualities. Generally, they still offer the best light sensitivity and produce somewhat less noise than CMOS sensors. Higher light sensitivity translates into better images in low light conditions. CCD sensors, however, are more expensive and more complex to incorporate into a video camera. A CCD can also consume as much as 100 times more power than an equivalent CMOS sensor.
CMOS Technology
Recent advances in CMOS sensors bring them closer to their CCD counterparts in terms of image quality. CMOS sensors lower the total cost for cameras since they contain all the logics needed to build cameras around them. In comparison with CCDs, CMOS sensors enable more integration possibilities and more functions for bright light condition. CMOS sensors also have a faster readout (which is advantageous when high-resolution images are required under bright light condition), however, are less desirable for low light condition and produce more noise. They use lower power dissipation at the chip level, as well as a smaller system size. Megapixel CMOS sensors are more widely available and are less expensive than megapixel CCD sensors.
Megapixel Sensors
For cost reasons, many megapixel sensors (i.e., sensors containing a million or more pixels) in megapixel cameras are the same size as or only slightly larger than VGA 4:3 sensors that provide a resolution of 640x480 (307,200) pixels. This means that the size of each pixel on a megapixel sensor is smaller than on a 640X480 sensor. For instance, a megapixel sensor such as a 1/3-inch, 2-megapixel sensor has pixel sizes measuring 3 um (micrometers/microns) each. By comparison, the pixel size of a 1/3-inch VGA sensor is 7.5 μm. So while the megapixel camera provides higher resolution and greater detail but at reduced sensitivity than its 640 X 480 (VGA) counterpart since the pixel size is smaller and light reflected from an object is spread to more pixels.
Image Scanning Techniques
Interlaced scanning and progressive scanning are the two image scanning techniques available today for reading and displaying information produced by image sensors. Interlaced scanning is used mainly in CCDs. Progressive scanning is used in either CCD or CMOS sensors. Astronomical video cameras can make use of either scanning technique. (Analog cameras, however, can only make use of the interlaced scanning technique for transferring images over a coaxial cable and for displaying them on analog monitors.)
Interlaced Scanning
When an interlaced image from a CCD is produced, two fields of lines are generated: a field displaying the odd lines, and a second field displaying the even lines. However, to create the odd field, information from both the odd and even lines on a CCD sensor is combined. The same goes for the even field, where information from both the even and odd lines is combined to form an image on every other line.
When transmitting an interlaced image, only half the number of lines (alternating between odd and even lines) of an image is sent at a time, which reduces the use of bandwidth by half. The monitor, for example, must also use the interlaced technique. First the odd lines and then the even lines of an image are displayed and then refreshed alternately at 25 (PAL) or 30 (NTSC) frames per second so that the human visual system interprets them as complete images. All analog video formats and some modern HDTV formats are interlaced.
However, when interlaced video is shown on progressive scan monitors such as computer monitors, which scan lines of an image consecutively, the artifacts become noticeable. The artifacts, which can be seen as “tearing”, are caused by the slight delay between odd and even line refreshes as only half the lines keep up with a moving image while the other half waits to be refreshed. It is especially noticeable when the video is stopped and a freeze frame of the video is analyzed. Odd and even line combination increase sensitivity effectiveness.
Interlaced video is video captured at 60 pictures (known as fields) per second, of which every 2 consecutive fields (at half height) are then combined into 1 frame. Interlacing was developed many years ago for the analog TV world and is still used widely today in all modern television and video monitors. It provides good results when viewing motion in standard TV pictures. To view interlaced video on e.g. a computer monitor, the video must first be de-interlaced, to produce progressive video, which consists of complete images, one after the other, at 30 frames per second.
When transmitting an interlaced image, only half the number of lines (alternating between odd and even lines) of an image is sent at a time, which reduces the use of bandwidth by half. The monitor, for example, must also use the interlaced technique. First the odd lines and then the even lines of an image are displayed and then refreshed alternately at 25 (PAL) or 30 (NTSC) frames per second so that the human visual system interprets them as complete images. All analog video formats and some modern HDTV formats are interlaced.
However, when interlaced video is shown on progressive scan monitors such as computer monitors, which scan lines of an image consecutively, the artifacts become noticeable. The artifacts, which can be seen as “tearing”, are caused by the slight delay between odd and even line refreshes as only half the lines keep up with a moving image while the other half waits to be refreshed. It is especially noticeable when the video is stopped and a freeze frame of the video is analyzed. Odd and even line combination increase sensitivity effectiveness.
Interlaced video is video captured at 60 pictures (known as fields) per second, of which every 2 consecutive fields (at half height) are then combined into 1 frame. Interlacing was developed many years ago for the analog TV world and is still used widely today in all modern television and video monitors. It provides good results when viewing motion in standard TV pictures. To view interlaced video on e.g. a computer monitor, the video must first be de-interlaced, to produce progressive video, which consists of complete images, one after the other, at 30 frames per second.
Progressive Scanning
With a progressive scan image sensor, values are obtained for each pixel on the sensor and each line of image data is scanned sequentially, producing a full frame image. In other words, captured images are not split into separate fields as with interlaced scanning. With progressive scan, an entire image frame is sent over a network and when displayed on a progressive scan computer monitor, each line of an image is put on the screen one at a time in perfect order. Result is less sensitivity compared to a interline sensor.
RGB or CMYK?
With the advent of CMYK and the CMOS splitter technology. Standard RGB matrix has filters that absorb 2/3 of the light spectrum before it hits each pixel. Each RGBG box is then combined with adjacent box elements to increase resolution. Total sensitivity is reduced by 2/3. YCMK, Rocks video cameras, uses subtractive colors which absorb 2 sections of the light spectrum. These cameras loose only 1/3 of the sensitivity compared to Mono ( resolution is same as RGBG )
The new splitter technology, used in CMOS camera of the DS16c, shunts parts of the spectrum to adjacent pixels so that virtually all photons are recorded. Sensitivity is virtually the same. Resolution is, of course, reduced.
The new splitter technology, used in CMOS camera of the DS16c, shunts parts of the spectrum to adjacent pixels so that virtually all photons are recorded. Sensitivity is virtually the same. Resolution is, of course, reduced.
What's the Difference Between Various MallinCam Cameras?
Each of MallinCam's cameras is designed and built for specific purposes -- and to meet different budgets. But budget is only
part of the equation. Intended use and purpose and what it takes to make the images are the main differences.
For the most part, the MallinCam "Video" cameras such as Micro, Jr PRO, Xtreme and Xterminator (A) are intended for live video display. Their main purpose is to display celestial objects and increase electronically aperture of any given telescopes as quickly and simply as possible on standard video displays. And they're designed to be self-contained and self supporting. They don't need computers or software for operation. Most of them "can" be controlled by computers for convenience, and with appropriate capture devices (which convert the video signals into digital signals computers can deal
with), "can" be attached to computers and the digitized images saved for future image-processing, but they don't have to be.
For instant-gratification star-gazing and public outreach or personal increase in aperture electronically, all it takes is the
camera, a video cable, a TV or video monitor, and a power source. That's it.
Naturally, there are compromises in this type of camera to allow it to do what it does so well. Because most people who do
live video presentations don't want to wait minutes or hours to get an image, these cameras are designed for maximum
sensitivity -- to reduce exposure times. That means they need and have sensors with extremely large pixels. The larger the
pixel, the more sensitive it has. To keep sensor size reasonable and cost reasonable and camera size and weight reasonable,
these large pixel high sensitivity sensors are relatively small (1/2" diagonal) and therefore also have relatively resolution made
for TV monitors, projectors, and frame grabbers etc.
A couple of years ago Rock Mallin created a poll on MallinCam Yahoo Groups and asked the users what was more important to them --
sensitivity or resolution. For the live video portion of the users, sensitivity was overwhelmingly the most important factor.
And that's what the high-end Xterminator line of cameras is for -- to be the fastest, most sensitive self-contained video-astro
camera possible. The other MallinCam video cameras offer less sensitivity and fewer features, but also at lower costs and in
smaller packages.
Most of the other MallinCam USB type computer only cameras are not as sensitive for live video, and they do require
a computer to save and manipulate their digital images. These cameras not only require a computer and appropriate
software, but they're nowhere near as sensitive and require much longer exposures. On the other hand, most of them also
have higher resolution and with an appropriate number of frames and image-processing, are capable of "cleaner"
images. But to achieve those results, the user might need several minutes of exposures, the computer, and the software
and skills to create the "better" images. And because the cameras aren't as sensitive, they'll require longer exposures --
often meaning guiding and a smoother mount.
The Universe camera does some of both. It does require longer exposures and it does require a computer. But with an
appropriate computer and appropriate software, it's capable of live video. It's also the largest
and heaviest camera MallinCam makes.
part of the equation. Intended use and purpose and what it takes to make the images are the main differences.
For the most part, the MallinCam "Video" cameras such as Micro, Jr PRO, Xtreme and Xterminator (A) are intended for live video display. Their main purpose is to display celestial objects and increase electronically aperture of any given telescopes as quickly and simply as possible on standard video displays. And they're designed to be self-contained and self supporting. They don't need computers or software for operation. Most of them "can" be controlled by computers for convenience, and with appropriate capture devices (which convert the video signals into digital signals computers can deal
with), "can" be attached to computers and the digitized images saved for future image-processing, but they don't have to be.
For instant-gratification star-gazing and public outreach or personal increase in aperture electronically, all it takes is the
camera, a video cable, a TV or video monitor, and a power source. That's it.
Naturally, there are compromises in this type of camera to allow it to do what it does so well. Because most people who do
live video presentations don't want to wait minutes or hours to get an image, these cameras are designed for maximum
sensitivity -- to reduce exposure times. That means they need and have sensors with extremely large pixels. The larger the
pixel, the more sensitive it has. To keep sensor size reasonable and cost reasonable and camera size and weight reasonable,
these large pixel high sensitivity sensors are relatively small (1/2" diagonal) and therefore also have relatively resolution made
for TV monitors, projectors, and frame grabbers etc.
A couple of years ago Rock Mallin created a poll on MallinCam Yahoo Groups and asked the users what was more important to them --
sensitivity or resolution. For the live video portion of the users, sensitivity was overwhelmingly the most important factor.
And that's what the high-end Xterminator line of cameras is for -- to be the fastest, most sensitive self-contained video-astro
camera possible. The other MallinCam video cameras offer less sensitivity and fewer features, but also at lower costs and in
smaller packages.
Most of the other MallinCam USB type computer only cameras are not as sensitive for live video, and they do require
a computer to save and manipulate their digital images. These cameras not only require a computer and appropriate
software, but they're nowhere near as sensitive and require much longer exposures. On the other hand, most of them also
have higher resolution and with an appropriate number of frames and image-processing, are capable of "cleaner"
images. But to achieve those results, the user might need several minutes of exposures, the computer, and the software
and skills to create the "better" images. And because the cameras aren't as sensitive, they'll require longer exposures --
often meaning guiding and a smoother mount.
The Universe camera does some of both. It does require longer exposures and it does require a computer. But with an
appropriate computer and appropriate software, it's capable of live video. It's also the largest
and heaviest camera MallinCam makes.