NASA’s Curiosity rover vehicle, that landed on Mars on August 6th, has sent back its first color images of the planet’s dusty yellow/orange landscape. The image was taken with the camera on the rover’s still retracted robotic arm, from behind the dust shield designed to protect the camera. The dust shield will be removed, promising better images, once the dust kicked-up by its landing has settled. This camera, known as MAHLI (Mars Hand Lens Imager), is primarily intended for examining close-up items. Still better images should come once the two Mastcams start sending back images.
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| The first color image from the Curiosity rover on Mars. The image was shot from using the camera on the rover’s robotic arm and is angled because that arm is still retracted. The image has been overlayed onto a computer rendering of the landscape, based on data from orbiting craft. Image credit: NASA/JPL-Caltech/Malin Space Science Systems |
All three cameras are built around Kodak KAI-2020CM sensors – 2MP CCD chips very similar in size to the 1″ type sensors used in Nikon’s 1 System and Sony’s DSC-RX100. These 11.8 x 8.9mm sensors are now made by Truesense Imaging – the company spun-out of Kodak in 2011. The All three are equipped with standard Bayer filters, allowing them to capture color images in a single shot.
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| The KAI-2020 sensors used by the rover’s main cameras, now made by Truesense Imaging |
The MAHLI camera has a 21.3mm (60mm equiv.) lens, though its effective field-of-view narrows to nearer 70mm equiv, F9.8 when working at its closest focus distance of 25mm. To allow working at such close range, the unit is equipped with two white LEDs and two ultraviolet LEDs, to allow it to test for fluorescence. The filters on MAHLI mean that, much like a conventional camera, it is only sensitive to visible light (in this instance, a 380–680nm range). MAHLI is designed to focus-stack images shot at different focus points, to maximise depth-of-field.
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| An artist’s impression of the Curiosity rover, showing the rough positions of the three primary imaging cameras. |
The two Mastcams, built onto the rover’s main mast, are much more sophisticated units. Although based around the same sensors, these have no IR filter, so are sensitive across the visible and near-infrared region of the spectrum. The cameras each include 9 filters that can be swapped in and out, to allow them to assess very specific colors and include ‘clear’ IR filters, to allow them to take full-color images.
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| The Mastcams feature the same underlying design, including a Filter Wheel containing nine filters that can be slotted into place to measure different light frequencies in the scene. |
The two cameras differ in terms of the prime lens they’re fitted with. Lens distortions mean their images are likely to be 1200 x 1200 pixels taken from the middle of each frame. Mastcam 34 features a 115mm equivalent F8 lens, while the Mastcam 100 uses a 343mm equivalent F11 lens. In addition to thier specific color filters, each has a more dense color filter to allow images to be shot while pointing towards the sun.
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| A test image shot from Malin Space Science System’s cleanroom, showing the full 1648 x 1200 pixel output of the Mastcam 34. Only the central 1200 x 1200 region of the image would be used. Image credit: NASA/JPL-Caltech/Malin Space Science Systems |
Both cameras are able to capture 720p video at around 7 frames per second, and the Mastcam 34 can be used to shoot 360 degree panoramas of the rover’s current position (taking 150 images over a 25 minute period as the remote mast is rotated). The operating team says it might use the rover’s movement to create cinematic tracking shots of the Martian landscape.
Each camera features 8GB of storage and can broadcast thumbnail images, so that time isn’t spent transmitting every image at full resolution, back from the surface of Mars. To ensure images don’t all come back with a yellow/orange tinge, Curiosity features color calibration and white-balance targets that the cameras can be pointed at.
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| The calibration target used by MAHLI, including a 1909 Lincoln penny and color targets, including a fluorescent pigment that glows red under UV light. Image credit: NASA/JPL-Caltech/Malin Space Science Systems |
It had been hoped that zoom lenses would be used for the Mastcams, but minor precision failures meant they weren’t ready in time for the mission’s launch. Malin Space Science Systems, the San Diego, California company that developed all the rover’s cameras, has said it will continue to work on the lenses for future projects.
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