Improve Your Telescope With a Security Camera Sensor

When it comes to viewing nebulae, galaxies, and other deep-sky objects, amateur astronomers on a budget have had two options. They can view with the naked eye through a telescope and perceive these spectacular objects as faint smudges that don’t even begin to capture their majesty, or they can capture long-exposure images with astrocameras and display the results on a view screen or computer, which robs the immediacy of the stargazing experience.

Stand-alone telescope eyepieces with active light amplification do exist for a real-time viewing, but commercial products are pricey, costing hundreds to thousands of dollars. I wanted something I could use for the public-astronomy observation nights that I organize in my community. So I decided to build a low-cost DIY amplifying eyepiece, to make it easier for visitors to observe deep-sky objects but without requiring a large financial investment on my part.

I quickly realized there was already an industry replete with hardware for handling low-light conditions—the security-camera industry. Faced with the challenge of monitoring areas with a variety of lighting, often using cameras spread out over a large facility, makers of closed-circuit television (CCTV) cameras created a video standard that uses digital sensors to capture images but then transmits them as HD-resolution analog signals over coaxial cables. By using this Analog High Definition (AHD) transmission standard, you can attach new cameras to preexisting long cable runs and still get a high-quality image.

A CMOS-image sensor module from a security camera [top left], a USB capture card [bottom left], and an OLED viewfinder [right] process analog video data.James Provost

While I didn’t need the long-distance capability of these cameras, I was very interested in their low price and ability to handle dim conditions. The business end of these cameras is a module that integrates a CMOS image sensor with supporting electronics. After some research, I settled on a module that combined a 2-megapixel Sony IMX307 sensor with a supporting NVP2441 chipset.

The key factor was choosing a sensor-chipset combination that supports something called Starlight or Sens-Up mode. This makes the camera more sensitive to light than the human eye, albeit at the cost of a little speed. Images are created by integrating approximately 1.2 seconds of exposure time on the sensor. That might make for choppy security footage, but it’s not noticeable when making observations of nebulae and other astronomical objects (unless of course something really weird happens in the sky!)

From Astronomy To Security Cameras and Back Again

The existence of the Sens-up mode is actually part of the technical heritage of digital imaging sensors. CMOS sensors were developed as a successor to charge-coupled devices (CCDs), which were eagerly embraced by the astronomical community following their introduction in 1970, replacing long-exposure photographic plates. However, the ability to take exposure frames as long as one second is rarely something that CCTV cameras are designed for: It can be more of a drawback than a feature, leading to blurred images of moving objects or people.

As a result, this capability is rarely mentioned in the product descriptions, and so finding the right module was the most challenging part: I had to buy three different camera modules before finally landing on one that worked.

The output from the camera module is passed to a digital viewfinder, which displays both the video and control menus generated by the module. These menus are navigated using a four-way, press-to-select joystick that connects to a dedicated header on the module.

The output of the camera is also passed to a capture card that converts the analog signal to digital and provides a USB-C interface, which allows images to be seen and saved using a smartphone. All the electronics can be powered via battery for complete stand-alone operation or from a USB cable attached to the capture card.

The analog HD module can be controlled directly using a joystick to navigate onscreen menus. Power can be provided externally via USB-C connector on the capture card or via an optional battery pack.James Provost

The components fit in an enclosure I made from 3D-printed parts, designed to match the 32-millimeter diameter of most telescope eyepieces for easy mounting. The whole thing cost less than US $250.

Testing out the Amplifying Eyepiece

I took my new amplifying eyepiece out with my Celestron C11 telescope to give it a try. Soon I had in my viewfinder the Dumbbell Nebula, also known as Messier 27/M27, which is normally quite hard to see. It was significantly brighter compared to a naked-eye observation. Certainly the difference wasn’t as marked as with a commercial rig that has noise-reducing cooling for the sensor electronics. But it was still an enormous improvement and for a fraction of the cost.

The Orion Nebula, some 1,340 light years away.Jordan Blanchard

The amplifier is also more versatile: You can remove it from the telescope, and with a 2.8-mm HD lens fitted to the camera-module sensor, you can use it as a night-vision camera. That’s handy when trying to operate in dark outdoor conditions on starry nights!

For the future, I’d like to upgrade the USB-C capture module to one that can handle the sensor’s digital output directly, rather than just the analog signal. This would give a noticeable boost in resolution when recording or streaming to a phone or computer. Beyond that, I’m interested in finding another low-cost camera module with a longer exposure, and refining the 3D-printed housing so it’s easier to build and adapt to other observing setups. That way the eyepiece will stay affordable, but people can still push it toward more serious electronically assisted astronomy.