ZWO Camera ASI 461 MM Pro Mono (84704)

ZWO Camera ASI 461 MM Pro Mono (84704)

The ASI461MM Pro is a high-performance cooled monochrome camera designed for demanding astrophotographers and professional astronomical research.

It features a large 44 × 33 mm Sony IMX461 CMOS sensor with an impressive 100 megapixels and a resolution of 11656 × 8750 pixels. Thanks to advanced back-illuminated (BSI) technology, the sensor delivers exceptional sensitivity, making it ideal for capturing extremely faint objects.

Back-Illuminated CMOS Technology (BSI)

In conventional front-illuminated sensors, incoming light must pass through metal wiring before reaching the photosensitive layer. This wiring reflects part of the light, reducing overall efficiency.

With a back-illuminated structure, light reaches the photosensitive surface directly from the rear side. The wiring layer is positioned beneath the active layer, allowing more photons to hit the sensor. As a result, more electrons are generated and collected in each pixel. This improves quantum efficiency—the ratio of photons converted into electrons—leading to significantly higher sensitivity and better performance in low-light conditions.

Two-Stage Cooling System

An integrated thermoelectric cooler (TEC) reduces the sensor temperature by up to 35°C below ambient temperature. At 0°C, dark current noise is only 0.003 electrons per second per pixel. During a 300-second exposure, this results in just 0.7 electrons of dark current—lower than the camera’s readout noise.

At –20°C, dark current drops even further to below 0.00024 electrons per second per pixel, allowing 5-minute exposures to remain virtually noise-free.

Anti-Dew Heating System

On clear nights, the front glass of the camera can cool significantly, causing condensation that may affect image quality. A thin polyimide heating element gently warms the protective window to prevent dew formation. The integrated anti-dew heater consumes approximately 5 watts and can be switched off when power conservation is necessary.

Zero Amp Glow Technology

Many traditional CMOS sensors produce a faint infrared glow during operation, visible in uncalibrated long exposures. This phenomenon, known as amp glow, typically appears in the corners of images.

The ASI461MM Pro uses advanced circuitry that completely eliminates amp glow, even during high-gain or long-exposure imaging. This feature is implemented directly in the firmware and requires no additional software configuration.

Monochrome Advantages

As a monochrome camera, the ASI461MM Pro offers higher sensitivity and resolution compared to color cameras. However, producing color images requires additional color filters and a filter wheel, as well as more processing effort.

Technical Specifications

Sensor and Imaging

• Sensor type: CMOS (Sony IMX461)

• Sensor size: 44 × 33 mm

• Resolution: 11656 × 8750 pixels

• Megapixels: 100

• Pixel size: 3.76 µm

• Bit depth: 16-bit

• Quantum efficiency: 91%

• Readout noise: 1.0 e⁻

• Full well capacity: 50,300 e⁻

• Frame rate: 3.77 fps (at full resolution)

• Color camera: No (monochrome)

Cooling and Performance

• Active cooling: Yes

• Maximum cooling difference: 35°C below ambient temperature

Connections and Interfaces

• Interface: USB 3.0

• Telescope connection: M68

• Flange focal distance: 22.5 mm

General Information

• Series: ASI 461

• Weight: 910 g

• Filter wheel included: No

Areas of Application

• Nebulae and galaxies: Yes

• Moon and planets: No

• All-sky and meteor observation: No

• Autoguiding: No