QHY268M / QHY268C-PH — APS-C Cooled CMOS Deep Sky Imaging Cameras

The QHY268 series uses Sony’s IMX571 back-illuminated APS-C sensor, a modern deep-sky imaging platform offering high quantum efficiency, ultra-low read noise, true 16-bit data output and zero amplifier glow. With 26 megapixels and 3.76µm pixels, this sensor resolves fine structures in nebulae and galaxies while maintaining a wide field of view and clean calibration performance.

The camera is available in monochrome (QHY268M) for maximum signal efficiency and narrowband flexibility, and colour (QHY268C) for simplified acquisition with a Bayer matrix. Both versions share identical electronics, cooling, readout modes and mechanical format.

Sensor Architecture and Image Performance

• Sensor: Sony IMX571 (APS-C, BSI CMOS, 26MP)
• Pixel Size: 3.76µm for fine detail sampling across a wide range of focal lengths
• Native 16-bit ADC: 65,536 intensity levels with smooth gradients and high dynamic range
• Back-Illuminated Structure: Higher photon conversion and improved low-signal response
• Zero Amp Glow: Simplifies calibration and enables clean deep integrations
• Low Read Noise: ~1.1e- to ~3.5e- depending on readout mode
• Extended Full-Well Mode: Up to ~75ke- to preserve highlights in bright regions

This combination makes the QHY268 platform well-suited to broadband galaxy fields, wide-field nebulae, multi-filter narrowband imaging, and long-integration deep sky projects.

Mechanical Design and System Integration

Both QHY268M and QHY268C share the same compact mechanical body. The back focal distance is 14.5mm (±0.2), providing space for filter drawers, rotators, OAG systems, and adapter trains. The chamber is sealed and desiccant-regulated, with a heated optical window to prevent condensation.

• Back Focus: 14.5mm (direct)
• Front Interface: M54 × 0.75
• Optional M48 adapters included
• Dual-Stage TEC Cooling: Approximately −35°C below ambient
• Internal Buffer: 1GB DDR3 for stable frame transfer
• Total Weight: ~810g

Readout Modes and Acquisition Control

The QHY268 series provides several readout modes to balance dynamic range, read noise, and gain structure. These modes are selectable in ASCOM, NINA, and SharpCap.

• Mode 0 – Photographic: General deep-sky imaging with balanced dynamic range
• Mode 1 – High Gain: Reduced read noise for narrowband and faint structures
• Mode 2 – Extended Full-Well: Preserves highlights in high dynamic range fields
• 2CMS Variants: Dual-sampling modes to further reduce read noise

The camera also includes:

• Thermal noise pattern stabilisation for consistent calibration frames
• UVLO protection to prevent damage from under-voltage power systems
• USB data clock tuning to minimise periodic horizontal banding
• Remote power-cycle reboot without USB reconnection (useful for observatories)

QHY268M vs QHY268C — Which to Choose

Specifications

Sensor: Sony IMX571, APS-C, BSI CMOS
Resolution: 6252 × 4176 (26MP)
Pixel Size: 3.76µm
A/D Conversion: Native 16-bit
Full-Well: ~51ke- (Std), ~75ke- (Extended)
Read Noise: ~1.1e- to ~3.5e- (mode dependent)
Dark Current: ~0.0005 e-/px/s @ −20°C
Shutter: Electronic Rolling
Interface: USB 3.0
Internal Buffer: 1GB DDR3
Cooling: Dual-stage TEC (~−35°C from ambient)
Back Focus: 14.5mm (±0.2)
Weight: ~810g

Multiple Readout Modes

Multiple Readout Modes are special for QHY 16-bit Cameras (QHY600/268/461/411).  Different readout modes have different driver timing, etc., and result in different performance. See details at “Multiple Readout Modes and Curves” Part.

Random change thermal noise suppression function

You may find some types of thermal noise can change with time in some back-illuminated CMOS cameras. This thermal noises has the characteristic of the fixed position of typical thermal noise, but the value is not related to the exposure time.  Instead, each frame appears to have its own characteristics.  The QHY600/268/461/411 use an innovative suppression technology that can significantly reduce the apparent level of such noise.

UVLO Protection

UVLO（Under Voltage Locking) is to protect the electronic device from damage caused by abnormally low voltages.

Our daily life experience tells us that the actual operational voltage of an electrical device must not significantly exceed the rated voltage, otherwise it will be damaged. For such precision equipment as cameras, long-term work at too low input voltage can also be detrimental to the working life of the camera, and may even make some devices, such as power manager, burn up due to long-term overload. In the all-in-one driver and SDK after 2021.10.23 stable version, the camera will give a warning when the input voltage of the camera is below 11V.

Optimizing USB Traffic to Minimize Horizontal Banding

It is common behavior for a CMOS sensor to contain some horizontal banding. Normally, random horizontal banding can be removed with multiple frame stacking so it does not affect the final image. However, periodic horizontal banding is not removed with stacking so it may appear in the final image. By adjust the USB traffic in Single Frame mode or Live Frame mode, you can adjust the frequency of the CMOS sensor driver and it can optimize the horizontal banding appeared on the image. This optimized is very effective to remove the periodic banding in some conditions.

A typical Periodic Horizontal Noise under certain USB_TRAFFIC values.

After Adjusting the USB Traffic to avoid the periodic horizontal noise.

Reboot the camera by power off and on

The camera is designed to use the +12V to reboot the camera without disconnecting and reconnecting the USB interface. This means that you can reboot the camera simply by shutting down the +12V and then powering it back on. This feature is very handy for remote controlling the camera in an observatory. You can use a remotely controlled power supply to reboot the camera. There is no need to consider how to reconnect the USB in the case of remote control.

 

In the Box

• QHY268 Camera Body (Mono or Colour)
• Locking 12V Power Cable
• 12V AC Adapter
• USB 3.0 Cable
• M54 to 2" Nosepiece
• Adapter Ring Kit
• Desiccant System
• Documentation