Parameters of CCD/CMOS detectors for Neutron or X-ray Imaging

The largest markets are for consumer cameras, industrial or security applications, and biological science, all of which have different requirements to neutron imaging. We use cameras designed for amateur astronomy, where the technical requirements are closest to those needed for neutron imaging (longer, low noise exposures with high dynamic range). We make small cameras for beam alignment, and large cameras for tomographic imaging.

In general, choose the smallest, cheapest camera compatible with your requirements, and eventually trade-up if necessary.

Our Choice of CCD and CMOS detectors.

Detector Slim CCD Slim CMOS Fast CMOS Square CMOS FS60 CCD VS60 CCD CMOS7.1 4/3" CMOS APS-C CMOS FullFrame ICON-L
Type Interline
No. Pixels 752 x 580 1920x1200 1600x1100 3000x3000 2759x2200 2759x2200 3208x2200 4144x2822 6248x4176 9576x6388 2048x2048
Diag. mm 8 (1/2") 13 (1/1.2") 17 (1.1") 16 (1.1") 16 (1") 16 (1") 17 (1.1") 23 (4/3") 28 (APS-C) 43 (35mm) 39 (square)
Image mm 6.46x4.81 11.25x7.03 14.4x9.9 11.3x11.3 12.53x9.99 12.53x9.99 14.4x9.9 19.1x13 23.5x15.7 36 x 24 27.6x27.6
Pixel size 8.6 µm 5.86 µm 9.0 µm 3.76 µm 4.54 µm 4.54 µm 4.5 µm 4.6 µm 3.76 µm 3.75 µm 13.5 µm
Q. effic ~75% ~80% ~80% ~80% ~70% ~70% ~75% ~90% ~90% 90%
Fullwell ~40,000 e- ~30,000 e- ~80,000 e- ~50,000 e- ~20,000 e- ~20,000 e- ~20,000 e- ~66,000 e- ~50,000 e- ~50,000 e- 100,000 e-
Read noise 10 e- 7 e- 5 e- 3 e- 5 e- 6 e- 3 e- 1.2-7.3 e- 1.0-3.3 e- 1.5-3.5 e- 2.9 e-
Dark e-/p/s <0.1@25°C ~1.0@45°C ~2.5@45°C 0.001@-20°C 0.0004@-10°C 0.0004@-10°C 0.03@-10°C 0.002@-20°C 0.003@0°C 0.003@0°C .0004@-70°C
Cooling uncooled uncooled uncooled uncooled/Δ-35°C Δ-27°C Δ-35°C Δ-35°C Δ-35°C Δ-35°C Δ-35°C Δ-70°C
Frame Rate 0.5 fps 18 fps *120 fps ^20-100 fps 0.2 fps 1 fps 30 fps 16 fps 3.5 fps 3 fps 1 fps
A/D Readout 16-bits 12-bits 12-bits 14-bits 16-bits 16-bits 12-bits 14-bits 16-bits 16-bits 16-bits
Binning hardware software software software hardware hardware software software software software hardware
Lens Type Tam f/1.0 Tam f/1.2 Fuji f/1.4 Fuji f/1.4 Fuji f/1.4 Fuji f/1.4 Fuji f/1.4 M43 f/0.95 M43 f/0.95 50mm f/1.2 50mm f/1.2
Mount CS- C- C-M43- C-M43- C-F- C-F- C-F- M43- M43-F- F- F-
Usual Dist 150mm 150mm 200mm 200-500mm 200-500mm 200-500mm 200-500mm 200-500mm 350-500mm 500mm 500mm
Usual FOV 75 x 50mm 100x100mm 100x100mm 100x100mm 100x100mm 200x250mm 200x250mm 200x250mm 200x250mm 200x250mm 200x250mm
Pixel @FOV 150 µm 85 µm 90 µm 35-70 µm 45-90 µm 90 µm 90 µm 60 µm 50 µm 30 µm 100 µm
Trigger Software Software Software Software Software Software/GPIO Software Software Software Software Software
Interface USB 2.0 USB2/GigE USB3/GigE USB3 USB2/GigE USB2 USB3/GigE USB3 USB3 USB3 Andor
1 1 1.5 1.7-2 4 6 5 3 5 9 50

     The Andor ICON-L is shown for comparison. The collimation and quality of your neutron beam-line will usually be the limiting factor for neutron imaging, not the camera.

Choosing an Imaging Camera - More is not always Better

  • A Lens aperture of f/1.0 transmits x2 as much light as an aperture of f/1.4, so fast lenses have advantages.
  • The lens flange-focal distance limits the choice of available lenses. Mirrorless CMOS cameras have much shorter FFDs (~20mm) than older SLR-type cameras (~45mm).
  • The FFD can be increased for some lenses, by using extension rings as for Macro photography but that increases the effective focal length and reduces the aperture.
  • The Optical path length depends on the required Field-Of-View (FOV), the lens focal length and the detector chip dimensions - see: Qioptiq.
  • The Overall efficiency depends on the ratio of the area of the FOV to the area of the detector, so don't choose a FOV larger than necessary.
  • More pixels means smaller pixels that collect less light. Resolution will be limited by your beam collimation and scintillator thickness, not the detector.
  • Pixel area is proportional to light collection. Combining adjacent small pixels (binning) can be used to emulate large pixels.
  • Quantum Efficiency is just the conversion efficiency, and takes no account of the much more important pixel area.
  • Full Well Capacity is the number of electrons that can be stored in a pixel, increasing the dynamic range of intensities: it increases with pixel area.
  • Read Noise is introduced simply by reading out the pixel charge, and is lower for CMOS than for CCD technology.
  • Dark Current is electron noise due to the temperature of the detector, and is lower for CCD than for CMOS technology. CCDs are better for long exposures (>60s).
  • Cooling reduces Dark Current, but with modern detectors little is gained below 0oC because of other noise sources, and long-term radiation damage.
  • Pixel Filtering by imageJ can also reduce noise, by replacing isolated bright pixels by the average of their surroundings.
  • Read Times are much shorter for CMOS than for CCD technology, where slow readout is favoured to reduce readout noise.
  • A/D readout determines the Dynamic Dange, and is usually much higher than the 8-bits (256) intensity levels seen by the human eye.
  • Binning increases the effective area of a pixel, and the light collected. Hardware binning increases the frame rate.
  • Trigger signals are used to synchronise exposures with sample rotation for tomography. Usually this can be accomplished with software.
  • The camera interface limits the raw frame rate. High intensities are needed for short exposures and fast frame rates
         USB 2.0 (theoretical 480 Mbps) is limited in practice to <280 Mbits/s i.e for a 2048x2048x16-bit camera to <4 frames/sec (fps)
         USB 3.0 (theoretical 5 Gbps) is limited in practice to <4000Mbits/s i.e for a 2048x2048x16-bit camera to <64 frames/sec (fps)
       * With <10 ms exposures, ~120 fps is achieved for 1600x1100 8-bit pixels or 1200x1000 12-bit pixels over >10m active USB3.2 (1x1) cables i.e. 1.7 Gbps
       ^ With 50 ms exposures, 20 fps is achieved with the square CMOS camera for 3000x3000 14-bit pixels over >10m active USB3.2 (1x1) cables i.e. 2.5 Gbps
       ^ With 10 ms exposures, 100 fps is achieved with x3 hardware binning in SharpCap for 16-bit pixels over >10m active USB3.2 (1x1) cables i.e. 1.6 Gbps
  • The cost depends partly on the technology, but also on the market - how many are sold, and what the customer is willing to pay. Mass market products are cheaper.