By Christopher Go, with QHY5III462C
By Christopher Go, with QHY5III462C+IR850 Filter
By Christopher Go, with QHY5III462C+ IR890 Filter
【Triple Transit and Mutual Events】
Photographer: Christopher Go
Camera: QHY5III462C
Integration: 3hrs
The QHY5III462 camera is built around Sony’s sixth-generation 2.1MP IMX462 STARVIS CMOS sensor. Featuring a 2.9μm pixel size, it shares identical dimensions and resolution with the sensor in the QHY5III290, a favorite among elite planetary astrophotographers. Consistent with other models in the 5III lineup, the QHY5III462 operates through USB 3.0 for both power and control–no extra power source is needed.
This back-illuminated IMX462 sensor introduces notable advancements over other planetary imaging sensors. Firstly, it includes sHCG (Super High Conversion Gain), ensuring minimal read noise even at high gain–perfect for stacking large numbers of short exposure planetary shots. Secondly, the sensor boasts remarkable sensitivity in the near-infrared (NIR) range.
In this latest sensor generation, Sony has deepened the photodiode wells beyond previous back-illuminated sensor designs. This allows longer-wavelength photons to reach deeper into the substrate, significantly boosting red and NIR light sensitivity. Moreover, since the RGB color filters become transparent in the NIR range, the sensor achieves nearly equal peak sensitivity in both visible and NIR spectra.
At around 800nm in the NIR spectrum, the sensor's quantum efficiency matches that of visible light. For planetary imagers using methane filters, which transmit light near 880nm, this is an excellent benefit.
Back-illuminated CMOS sensors offer enhanced sensitivity. In front-illuminated sensors, photons must travel through the metal wiring placed above the photosensitive area, reflecting some light and reducing effectiveness.
With back-illuminated architecture, light enters from the opposite side, bypassing the wiring that now sits beneath the light-sensitive layer. This ensures more photons reach the photodiode area, generating more electrons per photon. This photon-to-electron conversion rate–known as quantum efficiency–improves. A higher quantum efficiency means the sensor is better at capturing faint images.
One might assume each generation of Sony’s Exmor sensors improves upon the last. Yet, this wasn’t the case between the fifth and fourth generations of Exmor R sensors.
Earlier back-illuminated sensors featured shallower pixel wells, like those in third-gen front-illuminated sensors, unlike the deeper pixels of the fourth generation. Though the back-illuminated design doubled visible light sensitivity, it didn’t enhance NIR performance. This issue is resolved with the sixth-generation sensors, such as the IMX462. These combine back-illumination with deeper photodiodes, greatly boosting responsiveness across both visible and NIR wavelengths.
An additional strength of the QHY5III462 is its “Super High Conversion Gain” feature. This uses lower capacitance to amplify minimal charge into a high-voltage signal, improving performance under dim lighting. At high gain, the camera can achieve a read noise level as low as 0.5 electrons!
The comparison images below showcase this improvement over the IMX290 sensor. The left image from the QHY5III462C is brighter than the corresponding QHY5III290C on the right. Identical low-light settings and UV/IR filters were used for each comparison. This test highlights the QHY5III462C’s improved sensitivity and signal-to-noise ratio in visible light conditions.
The IMX462’s filter matrix uses organic dyes. These filters perform well in the visible spectrum but become transparent in the NIR range. Therefore, achieving accurate RGB color requires an external UV/IR filter to block NIR wavelengths.
Unlike many color cameras that incorporate a built-in UV/IR filter, the QHY5III462C avoids this to maximize NIR capabilities. Instead, it features an AR-coated optical window without any UV or IR filtering. It comes with two 1.25″ screw-on filters: one UV/IR cut filter for standard RGB imaging, and one IR850 filter to block visible light while allowing wavelengths above 850nm to pass.
