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.

Note: †FS60 and †VS60 CCD cameras are being phased out. Distances are approximate.

Detector Slim CMOS Fast CMOS Square CMOS Cooled CMOS †FS60 CCD †VS60 CCD 4/3" CMOS APS-C CMOS FullFrame ICON-L
Type Pregius
IMX174		 Pregius
IMX432		 Pregius
IMX533		 Cooled
IMX533		 Interline
ICX694		 Interline
ICX694		 Pregius
IMX294		 Pregius
IMX571 		Pregius
IMX455		 Andor
ICON-L
No. Pixels 1920x1200 1600x1100 3000x3000 3000x3000 2759x2200 2759x2200 4144x2822 6248x4176 9576x6388 2048x2048
Diag. mm 13 (1/1.2") 17 (1.1") 16 (1.1") 16 (1.1") 16 (1") 16 (1") 23 (4/3") 28 (APS-C) 43 (35mm) 39 (square)
Image mm 11.25x7.03 14.4x9.9 11.3x11.3 11.3x11.3 12.53x9.99 12.53x9.99 19.1x13 23.5x15.7 36 x 24 27.6x27.6
Pixel size 5.86 µm 9.0 µm 3.76 µm 3.76 µm 4.54 µm 4.54 µm 4.6 µm 3.76 µm 3.75 µm 13.5 µm
Q. effic ~80% ~80% ~80% ~80% ~70% ~70% ~90% ~90% 90%
Fullwell ~30,000 e- ~80,000 e- ~50,000 e- ~50,000 e- ~20,000 e- ~20,000 e- ~66,000 e- ~50,000 e- ~50,000 e- 100,000 e-
Read noise 7 e- 5 e- 3 e- 3 e- 5 e- 6 e- 1.2-7.3 e- 1.0-3.3 e- 1.5-3.5 e- 2.9 e-
Dark e-/p/s ~1.0@45°C ~2.5@45°C ~2.5@45°C 0.001@-20°C 0.0004@-10°C 0.0004@-10°C 0.002@-20°C 0.003@0°C 0.003@0°C .0004@-70°C
Cooling uncooled uncooled uncooled Δ-35°C Δ-27°C Δ-35°C Δ-35°C Δ-35°C Δ-35°C Δ-70°C
Frame Rate 18 fps *120 fps ^20-100 fps ^20-100 fps 0.2 fps 1 fps 16 fps 3.5 fps 3 fps 1 fps
A/D Readout 12-bits 12-bits 14-bits 14-bits 16-bits 16-bits 14-bits 16-bits 16-bits 16-bits
Binning software software software software hardware hardware software software software hardware
Lens Type Tam f/1.2 Fuji f/1.4 16mm f/1.4 25mm f/1.4 16mm f/1.4 25mm f/1.4 35mm f/0.95 35mm f/0.95 50mm f/1.2 50mm f/1.2
Mount C- C-M43- C-M43- C-M43- C- C- M43- M43-F- F- F-
Usual Dist 150mm 200mm 150mm 500mm 200mm 550mm 600mm 500mm 500mm 500mm
Usual FOV 100x100mm 100x100mm 100x100mm 200x200mm 125x100mm 250x200mm 250x200mm 250x200mm 250x200mm 250x200mm
Pixel @FOV 85 µm 90 µm 35 µm 70 µm 45 µm 90 µm 60 µm 50 µm 30 µm 100 µm
Trigger Software Software Software Software Software Software/GPIO Software Software Software Software
Interface USB2/GigE USB3/GigE USB3 USB3 USB2/GigE USB2 USB3 USB3 USB3 Andor
Cost
Detect+Lens		 1 1.5 1.7 2 4 6 3 5 9 50

     The Andor ICON-L is shown for comparison - we do not sell it. 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 - Bigger 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 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 it 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 usually 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.
  • Cooling reduces Dark Current, but with modern detectors little is gained below 0oC because of other noise sources, and long-term radiation damage "noise".
  • 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 Dynamic Range, and is much higher than the 8-bits (256 levels) seen by the human eye. 14-bits is good for imaging, 16-bits is optimistic.
  • 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 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.

    • Relative speed and resolution of cameras

    Larger detectors can gather more light, provided suitable lenses are available. For example, our classic 250x20mm camera with a 36x24mm fullframe IMX455 detector and a fast f/1.2 lens can be compared to a smaller 24x16mm APS-C IMX571 detector with an even faster f/0.95 lens.

  • The relative camera speed for a given FOV is the ratio of the chip areas or 24x16/(36x24)x0.95x0.95/(1.2x1.2)=0.71.
    So the IMX571+f/0.95 camera is 71% as fast as the bigger IMX455+f/1.2 camera.
  • The "optical" resolution is just the FOV divided by the number of 3.76µ pixels.
    It is 200/4176=48µ for the IMX571+f/0.95 camera and 200/6388=31µ for the IMX455+f/1.2 camera.

    In practice the real resolution is limited to 50µ or more by the beam divergence, scintillator thickness etc.
    So the smaller, cheaper IMX571+f/0.95 camera has equally good resolution and is still 71% as fast as the bigger more expensive IMX455+f/1.2 camera.
    Bigger is not always (much) better.

    Upgrade to CMOS from our earlier CCD cameras

    Our CMOS cameras have higher efficiency and resolution, with faster readout, than our earlier CCD cameras. The "slim CCD" used in our previous beam alignment cameras can be replaced by our "slim CMOS" detector, which is practically the same physical size but with a larger CMOS chip.

    Our old CCD imaging cameras based on the 1" Sony ICX694 12.5x10mm chip, in the FS60/VS60 using a large f/1.4 lens, can be replaced by our 36x24mm fullframe IMX455 detector and a fast f/1.2 lens, or our less expensive 24x16mm APS-C IMX571 detector with an even faster f/0.95 lens. The speed and resolution gain with the latter upgrade can be summarised as follows.

  • The relative camera speed for a given FOV is the ratio of the chip areas or 24x16/(12.5x10.0)x1.4x1.4/(0.95x0.95)=6.67
    So the IMX571+f/0.95 camera is x6.67 as fast as the 1" Sony ICX694 12.5x10mm VS60/FS60 camera !!
  • The "optical" resolution is just the FOV divided by the number of pixels.
    It is 200/4176=48µ for the IMX571+f/0.95 camera and 200/2200=91µ for the ICX694 12.5x10mm VS60/FS60 camera, a factor of x2.

    Upgrading to APS-C CMOS from our old 1" CCD imaging camera gives big gains in both speed and resolution
    for a quite modest cost (~€4500 or even less if you do it yourself).