NANO1 - Design
NANO1 is the world’s smallest astronomy camera. The small physical size means careful planning is required to get the best image quality out of it for astronomy purposes.
Today’s post will be about the astronomy-centric design we’ve put into the NANO1.
The key challenge to astronomy imaging is the very low amount of light available for the camera to form an image.
This usually means using a high ISO, which amplifies the image signal and noise at the same time;
Or using a long exposure time, which causes increased temperatures that induces more “random signals” that is picked up by the sensor. Both methods create more noise, resulting in a grainy image.
With the NANO1, TinyMOS designs around these challenges.
Back-Side Illuminated Sensor
At TinyMOS, we focus on using small sensor designs, which are inherently disadvantaged in using the high ISO method. To overcome the limitation, we chose a Back-side Illuminated CMOS sensor from Sony. The BSI technology allows more light to reach the photo-sensitive part of the sensor, allowing more photons to be converted to signal, thus improving low light sensitivity. This results in better images in low light.
Apart from sensor technology, we focus on reducing thermally induced noise in our design.
“Thermal noise is caused by the sensor heating up and releasing electrons (as any heat source does). Unfortunately the photosites cannot distinguish between electrons released as light, and electrons released as heat, so it tends to measure both. The longer the exposure, the hotter the sensor gets (to a point of course) and the higher the noise to data ratio making it harder to extract the data from the noise. “ Allan’s Stuff
By reducing the temperature of the image sensor, we can greatly reduce thermal noise.
Here’s how we do it:
Aluminum face plate
The face plate of NANO1 is machined out of aerospace grade aluminum, which is an excellent heat sink material. The large surface area of the face plate and an applied thermal-interface pad to the electronics, allows rapid transfer of heat from the electronics out of the camera to keep them cool.
The metal contact to the lens mount, makes use of the entire lens assembly as a heat sink, further reducing the temperature of the electronics.
External power operations
Battery is a key source of heat generation in small electronic devices such as the NANO1. The camera is designed to be able to function without internal battery, powered solely by the USB-C port. The removal of the battery further reduces heat generated in the camera, reducing thermal noise generation.
Internal heat sink block (possible feature)
We are investigating the possibility of inserting a heat sink block into the camera, in lieu of the battery. The heat sink block can be attached to a peltier cooler, lowering the sensor temperature below ambient temperature.
The other function of thermal noise is time. With greater exposure, there is a greater likelihood that random signals can be generated from the warm electronics. To reduce noise we need to reduce the length of the exposure.
To achieve that we designed for the following features:
Lenses and accessories
Large aperture optics
NANO1 will be released with a range of high F-ratio lenses. A high F-ratio means greater light intensity on the sensor, allowing for shorter exposure time. Our F/1.4 lens is 4x brighter than the F/2.8 kit lens on the NANO1. That means an exposure of 60 seconds can be captured in 15 seconds with our large aperture lenses. This means a 4x reduction in thermal noise read out by the circuit. The reduced operation time also reduces the heat generated for the next shot.
Prime focus capability
NANO1 is extremely small and can be reverse mounted on some telescopes. On the Celestron telescopes with Fastar technology, it means going from F/10 to F/2. A 25x reduction in exposure time and noise!
Interchangeable IR filter
NANO1 also features an interchangeable IR cut filter. By removing the filter, Hα emission, which gives the nebulae and other astronomy objects reddish color, can reach the sensor much more efficiently. That allows the sensor to pick up more details on such objects.
We look forward to placing the NANO1 in your hands, to capture images of the beautiful night skies. Help us by sharing about NANO1 on your social media.
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#updated 12/11/2018. Nebulae and some other Deep Sky Objects emits in Hα spectrum, which is at the edge of the visible range, but not within the Infrared Red light wavelengths. We mis-identified Hα as Infrared Red light for brevity and regret the mistake. Thank you Dr Liu Boyang for pointing our the mistake.