Large pixel CCD and megapixel CMOS cameras for neutron imaging.

Camera makers often emphasise the advantages of megapixel CMOS cameras, which are by far the most popular and usually the most suitable for commercial applications of optical imaging; they are also less expensive to make. CMOS cameras have advantages, but also disadvantages. Both CCD and CMOS cameras are optimized for imaging directly with light. The largest markets are for consumer cameras, industrial and security applications, and biological science, all of which have different requirements to neutron imaging. Expensive cameras are produced for biological science, but such cameras have few advantages for 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). See Why buy a camera instead of making one. Finally, neutron imaging has a radiation background that eventually damages or destroys the detector, and otherwise negates many of the advantages of expensive cameras.

CCD/sCMOS detectors. We can provide for the most expensive cameras, but price increases rapidly for minimal practical advantage.

Detector Slim CCD Compact CMOS HiRes CMOS Fast CMOS # FS14 # FS60 A383L+ ## LF40+ PCO.2000 #VS60 CMOS7.1 PCO.edge gold 4.2 COSMOS
Type Interline CCD
Pregius CMOS
Pregius CMOS
Pregius CMOS
Interline CCD
Interline CCD
FullFrame CCD
Interline CCD
Interline CCD
Interline CCD
Pregius CMOS
Scientific sCMOS
Resolution pixel 752 x 580 1920 x 1200 5472 × 3648 1600 x 1100 1392 x 1040 2759 x 2200 3326 x 2504 2048 x 2048 2048 x 2048 2759 x 2200 3208 x 2200 2048 x 2048 9576 x 6388
Image diag. mm 8 (1/2") 13 (1/1.2") 15.9 (1") 17 (1.1") 11 (2/3") 16 (1") 22.5 (4/3") 21.4 (4/3") 21.4 (4/3") 16 (1") 17 (1.1") 18.8 (4/3") 43.3 (35mm)
Image area mm 6.46x4.81 11.25x7.03 13.13x8.75 14.4x9.9 8.98x6.71 12.53x9.99 17.96x13.52 15.16x15.16 15.16x15.16 12.53x9.99 14.4x9.9 13.3 x 13.3 36.07 x 24.05
Pixel size µm* 8.6 x 8.3 5.86 x 5.86 2.4 x 2.4 9.0 x9.0 6.45 x 6.45 4.54 x 4.54 5.4 x5.4 7.4 x7.4 7.4 x7.4 4.54 x 4.54 4.5 x 4.5 6.5 x 6.5 3.75 x 3.75
Quantum effic* ~75% ~80% ~79% ~72% ~70% ~70% 55% 55% 55% ~70% ~75% >70% 87%
Fullwell e- ** ~40,000 ~30,000 ~15,000 ~80,000 ~20,000 ~20,000 ~30,000 ~40,000 ~40,000 ~20,000 ~20,000 ~30,000 ~50,000
Read noise e- ** 10 7 4 5 4 5 7 11 6 6 3 1 3
Dark c. e-/pix/s <0.1@25°C ~1.0@45°C ~2.0@45°C ~2.5@45°C 0.001@-10°C 0.0004@-10°C 0.01@-20 °C 0.01@-20°C 0.01@-20°C 0.0004@-10°C 0.03@-10°C <0.02@-30°C
Peltier Cooling uncooled uncooled uncooled uncooled Δ -27 °C Δ -27 °C Δ -40 °C Δ -40 °C Δ -50 °C Δ -35 °C Δ -35 °C Δ -30 °C Δ -35 °C
Read time (s)*** 0.3 41 fps 18 fps 69 fps 1 to 3 1 to 3 6 to 10.5 3 to 6 0.5 to 0.2 0.1 to 1 30 fps 40 fps 0.5
A/D Readout** 16-bits 12-bits 12-bits 12-bits 16-bits 16-bits 16-bits 16-bits 14-bits 16-bits 12-bits 16-bits 16-bits
Binning h,v x1 x2 x4 x8 software software software x1 x2 x4 x8 x1 x2 x4 x8 x1 x2 x4 x8 x1 x2 x4 x8 x1 x2 x4 x8 x1 x2 x4 x8 sofware x1 x2 x4 x1 x2
Mount CS-mount C-mount C-mount C-mount C-or F-mount C-or F-mount F-mount F-mount F-mount C- or F-mount C- or F-mount C- or F-mount F-mount
Trigger signals Software Software Software Software Software Software Software Software GPIO GPIO software GPIO Software
Interface*** USB 2.0 USB3 or GigE USB3 or GigE USB3 or GigE USB 2.0 USB 2.0 USB 2.0 USB 2.0 USB 3.0 USB 2.0 USB 3.0 USB 3.0 USB 3.0
Relative cost 1 1 1.5 2 2 4 3.5 5 20 4.5 4.0 16 8

#   The VS14 and VS60 are faster readout cameras with the same 2/3" or 1" Sony EXview HAD II (ICX) CCDs as the less expensive FS14 and FS60.
     Our larger "Kodak" (KAI) CCDs are read out more slowly to reduce noise. They are also used in much more expensive cameras with faster readout.
##  The LF40+ is no longer available, but can be replaced in the same camera box by the A383L+ which has similar performance.
     The collimation and quality of your neutron beam-line will usually be the limiting factor for neutron imaging, not the camera.

*   Light capture per pixel is proportional to the pixel area and its quantum efficiency (at 525nm)
     Fullwell Capacity is the number of electrons that can be stored without overflow (blooming)
     Fullwell Capacity is also proportional to pixel area, but also depends on anti-blooming design
     Noise can be "Dark current" due to thermal energy, or "Read noise" due to electronic readout
     Dark Current can be reduced by cooling for long exposures. Modern Sony ICX CCDs have exceptionally low dark current.
**  Dynamic range is the ratio of Fullwell capacity to Noise, & is lower than the 16-bit (65,536) readout
     Dynamic Range in Decibels DR= 20log (Fullwell capacity/Noise)dB eg typically DR= 5,000= 74dB
     Dynamic Range is often exagerated by neglecting dark noise (true only for very short exposures)
     Note that electron- or photon-multiplied cameras generally have a low dynamic range eg DR= 1,500= 64dB
     A high dynamic range means that contrast between slightly different intensities is better, important for imaging
*** USB 2.0 is limited in practice to ~280Mbits/s i.e for a 2048x2048x16 bit camera to ~4 frames/sec (fps)
     USB 2.0 is also sufficient for the 1920x1200 12-bit Sony Pregius CMOS camera up to 10 frames/sec (fps) over >10m active cables
     USB 3.0 is limited in practice to ~4000Mbits/s i.e for a 2048x2048x16 bit camera to ~64 frames/sec (fps) with short ~3m cables.

In our "interline" CCDs, charge accumulated by photo-sensitive columns is quickly transferred to adjacent storage columns. The advantage is that smearing is avoided during readout, so a mechanical shutter is not needed. Some of the chip area is used for storage, but that is compensated by using micro-lenses over every pixel. Sony sensors are typically ~75% sensitive to the mainly green (540nm) light emitted by neutron scintillators, and at that wavelength there is little advantage for more expensive "back-illuminated" CCDs. This explanations is simplified, but summarises why we use "slow" readout CCDs for neutron imaging.

Of the high-end cameras, the PCO.2000 uses the same Kodak KAI-4022 interline CCD as our LF40+ and has similar imaging performance, except that it uses more expensive electronics with faster readout. Our VS60 is a less-expensive fast readout CCD alternative to the CIS2020 sCMOS camera, whose main advantage is faster readout for lower readout noise (but higher dark current, which limits exposure times). The sCMOS camera is then best suited for fast imaging on high flux sources, while our cooled CCD cameras are best suited for lower flux imaging with longer acquisitions (>1s).

Our small cameras use Sony EXview HAD CCDs, which are very efficient, with low noise; the chips are also small, limiting imaging area but permitting the use of inexpensive fast C-mount lenses. Our f/1.0 lens is twice as fast as an f/1.4 lens. More important than the efficiency of the CCD itself, the efficiency of the camera is proportional to the ratio of the CCD to scintillator area, so our smaller CCDs are matched to our smaller cameras.