G4 cameras contain Full-Frame CCD chips OnSemi KAF with 36 × 36 mm detector area. These detectors are equipped with so-called “anti-blooming gate” (ABG), which drains the over-abundant charge from saturated pixels. ABG ensures the round images of bright stars, without disruptive blooming spikes. On the other side, compromising of the CCD linearity by ABG is only negligible. G4 cameras can be used for astrometric and photometric applications as well as for astrophotography.

No matter if your target is reliable scientific data or beautiful images of deep-sky objects, G4 CCD cameras are able to provide both.

G4 series contains the following camera models:

G4 CCD cameras are designed to work in cooperation with a host Personal Computer (PC). As opposite to digital still cameras, which are operated independently on the computer, the scientific slow-scan, cooled cameras usually require computer for operation control, image download, processing and storage etc. To operate G4 CCD camera, you need a computer which:

1. Is compatible with a PC standard.

2. Runs a modern 32 or 64 bit Windows operating system.

3. Provides at last one free USB port.

   Remark:

   The current series of G4 cameras are designed to operate with USB 2.0 high-speed (480 Mbps) hosts. Although they are fully backward compatible with USB 1.1 full-speed (12 Mbps) hosts, image download time can be somewhat longer if USB 1.1 connection is used.

G4 CCD Cameras Technical Specifications

CCD chip

G4 cameras use OnSemi Full-Frame CCD detectors with ABG (anti-blooming gate), ensuring images without excessive charge leaks from the overexposed portions of the image (blooming), e.g. bright stars in the field of view. ABG of these CCDs is designed for relatively low light levels (100× of saturation signal, compared to e.g. 300× of saturation signal ABG level of KAI-4022 CCD or 1000× of saturation signal ABG level of KAF-8300 CCD, intended for taking of images against sun etc.). Low ABG level does not to disrupt linear response to light.

Model G4-9000

G4-9000 model uses 9 MPx OnSemi KAF-09000 CCD.

Model G4-16000

G4-16000 uses 16 MPx OnSemi KAF-16803 CCD.

Camera Electronics

16-bit A/D converter with correlated double sampling ensures high dynamic range and CCD chip-limited readout noise. Fast USB interface ensures image download time within several tens of seconds.

Maximum length of single USB cable is 5 m. This length can be extended for instance to 10 m by using single USB hub or USB active extender cable. Up to 100 m extension can be achieved with third-party extender.

Image download time depends on the CCD chip used in particular camera model. Also the read noise depends on the chip as well as on the read mode.

• Standard read mode provides system read noise approx. 1 e^- above CCD chip read noise.

• LN (Low-noise) read mode is somewhat slower (approx. 1.2×), but ensures system read noise equal or smaller than the manufacturer-specified chip read noise.

Model G4-9000

The gain in binning modes of G4-9000 cameras was adjusted from 2.5 e-/ADU to 1.7 e-/ADU beginning with system driver version 2.3 to utilize the full A/D converter dynamic range, because particular detector output node cannot pass higher output signal levels either way.

Model G4-16000

G4-16000 cameras use the same gain for unbind and binned reading when used with system driver version 2.3 and higher. When older driver is used, stated gain 1.6 e-/ADU is used for 1×l binning only, while all other binning use 2.7 e-/ADU. Gain setting was unified to utilize the full A/D converter dynamic range, because particular detector output node cannot pass higher output signal levels either way.

Notes:

1. Binning can be combined independently on both axes

2. ULN read noise depends on the CCD chip itself. If the read noise of the particular chip is 7.5 e^- RMS, the system read noise is also 7.5 e^- RMS.

3. Download times can be somewhat longer when connected to USB 1.1 host.

Chip Cooling

Regulated two-stage thermo-electric chip cooling up to 40 °C below ambient temperature with forced air cooling and 0.1 °C temperature precision ensure very low dark current for long exposures.

Notes:

1. It is not recommended to cool the chip to the maximum temperature difference, else the camera cannot guarantee temperature stability when the ambient air temperature rises. It is usually practical to set the temperature so the cooling utilization varies around 90%. This provides enough reserve in cooling power to keep the CCD temperature even if the ambient temperature rises several degrees Celsius.

2. The cooling performance depends on the environmental conditions and also on the power supply. If the power supply voltage drops below 12 V, the maximum temperature difference is lower.

3. Camera construction does not allow usage of both air and liquid cooling. Combined cooling (air with the liquid cooling option) is not available, because such cooling does not work effectively enough with air only nor with water only.

Power supply

The 12 V DC power supply adapter enables camera operation from arbitrary power source including batteries, wall adapters etc. Universal 100–240 V AC/50–60 Hz, 60 W “brick” adapter is supplied with the camera. Although the camera power consumption does not exceed 30 W, the 60 W power supply ensures noise-free operation.

Notes:

1. Camera power consumption is measured on the AC outlet (230 V/50 Hz) of the 12 V power supply.

2. The camera contains its own power supplies inside, so it can be powered by unregulated 12 V DC power source—the input voltage can be anywhere between 10 and 14 V. However, some parameters (like cooling efficiency) can degrade if the supply drops below 11 V.

3. G4 CCD camera measures its input voltage and provides it to the control software. Input voltage is displayed in the Cooling tab of the CCD Camera control tool in the SIPS. This feature is important especially if you power the camera from batteries.

Mechanical Specifications

Compact and robust camera head measures only 154 × 154 × 65 mm (approx. 6 × 6 × 2.5 inches). The head is CNC-machined from high-quality aluminum and black anodized. The head itself contains USB-B (device) connector, 8-pin RJ45 connector for external filter wheel and 12 V DC power plug, no other parts (CPU box, USB interface, etc.), except a “brick” power supply, are necessary. Integrated mechanical shutter allows streak-free image readout, as well as automatic dark frame exposures, which are necessary for unattended, robotic setups.

Filter wheel if not integrated into camera head, it is necessary to use external filter wheel with 5 positions for 50 × 50 mm square filters. This external filter wheel is driven by the electronics already included into G4 camera head. Only single short 8-wire cable connects the filter wheel with the camera head and no separate power or communication cables are necessary for the external filter wheel. Also software (camera drivers, image acquisition applications) does not distinguish between internal and external filter wheel, camera works the same way like the G2 or G3 camera with integrated filter wheel.

Notes:

1. Back focal distance is “optical”, which means it calculates with refraction on the plan-parallel glass optical elements in the light path.

Optional accessories

Camera head can be combined with various accessories according to the requirements of the target application (optical system, used filters, guiding, etc.).

Telescope adapters

Large diagonal dimension of CCD detectors used in G4 cameras (52 mm) does not allow usage of common adapters, typically limited to 2 inches diameter (50.8 mm), like T-thread M42 × 0.75, M48 × 1 thread, Nikon bayonet etc. This is why G4 cameras are by default shipped with M68 × 1 threaded adapter.

Another alternative if Canon EOS photographic lens adapter, which has enough diameter not to cause significant vignetting. Adapter is designed for G4 cameras with external filter wheel, with which it keep the 44 mm back focal distance between bayonet front plate and CCD detector.

External Filter Wheels

Because large detectors if the G4 camera require large 50 × 50 mm filters, filter wheel cannot be placed inside the camera head and G4 cameras rely on external filter wheels only. There are two sizes of external filter wheels for G4 cameras available:

• The “M” sized wheel for 5 square filters 50 × 50 mm.

• The “L” sized wheel for 7 square filters 50 × 50 mm.

External filter wheels are described in detail here.

Off-Axis Guider adapter

The G4 off-axis guider (OAG) is designed to allow attachment of any guiding camera with 1.25" eyepiece nose, although the nose must be somewhat shorter to achieve focus. G0 cameras are designed to achieve focus with G4 OAG and a special shorter version of 1.25" nose with C-mount thread is available for all G1 cameras. Any camera with CS-mount (short version of C-mount standard) can use this adapter to be attached to G4 OAG.

The G4 OAG offers the M68 × 1 thread on the telescope side. The back focal distance is 61.5 mm.

Off-Axis Guider adapters are described in detail here.

Guiding cameras

G0 and G1 cameras are completely independent devices with their own USB connection to the host PC. They are mentioned here only not to omit an important part of the whole system.

G0 and G1 cameras can be used on the G4 OAG, on standalone guiding telescope or for any other imaging purpose, like Moon or planetary imaging etc. Both G0 and G1 camera can share the Gx Camera Ethernet Adapter with up to 3 other Gx cameras to be accessed over network.

G0 and G1 guider cameras are described in detail here.

Gx Camera Ethernet Adapter

Gx Camera Ethernet Adapter allows connection of up to 4 Gx cameras of any type on the one side and 1 Gbps Ethernet on the other side. This adapter allows access to connected Gx cameras using routable TCP/IP protocol over practically unlimited distance.

Gx Camera Ethernet Adapter devices are described in detail here.

Software Support

Powerful SIPS (Scientific Image Processing System) software supplied with the camera allows complete camera control (exposures, cooling, filters) with automatic sequences and complete image calibration. SIPS also supports advanced tools like Image Add tool with automatic sub-pixel image alignment, (L)RGB Add tool, Image Blink tool, image filters and many more functions.

SIPS software package is freely available for download from this www site.

Drivers for ASCOM standard as well as native drivers for third-party software are also available (e.g. TheSkyX, MaxIm DL, AstroArt, etc.). Visit the download page of this web site for current list of available drivers, please.

Automatic guiding

SIPS software package allows automatic guiding of the astronomical telescope mounts using separate guiding camera. Proper and reliable automatic guiding utilizing the computational power of Personal Computer (e.g. calculation of star centroid allows guiding with sub-pixel precision) is not simple task. Guiding complexity corresponds to number of parameters, which must be entered (or automatically measured).

The “Guiding” tool allows switching of autoguiding on and off, starting of the automatic calibration procedure and recalculation of autoguiding parameters when the telescope changes declination without the necessity of new calibration. Also swapping of the German Equatorial mount no longer requires new autoguider calibration. There is also a graph showing time history of guide star offsets from reference position in both axes. The length of graph history as well as the graph range can be freely defined, so the graph can be adjusted according to particular mount errors and periodic error period length. Complete log of calibration procedure, detected offsets, correction pulses etc. is also shown in this tool. The log can by anytime saved to log file.

An alternative to classic autoguiding is the inter-image guiding, designed for modern mounts, which are precise enough to keep tracking with sub-pixel precision through the single exposure, and irregularities only appear on the multiple-exposure time-span. Inter-image guiding then performs slight mount position fixes between individual exposures of the main camera, which eliminates “traveling” of the observed objects through the detector area during observing session. This guiding method uses main imaging camera, it does not use another guiding camera and naturally does not need neither OAG nor separate guiding telescope to feed the light into it.

Shipping and Packaging

G4 CCD cameras are supplied in the foam-filled, hard carrying case containing:

• Camera body with a user-chosen telescope adapter. The M68 × 1 adapter is included by default, Canon EOS adapter is available at additional cost.

• A 100-240 V AC input, 12 V DC output “brick” adapter with 1.8 m long power cable.

• 5 m long USB A-B cable for connecting camera to host PC.

• A CD-ROM with camera drivers, SIPS software package with electronic documentation and PDF version of User's Manual.

• A printed copy of camera User's Manual.

Image Gallery

Example images captured with G4 cameras.

All images published with permission of their respective authors.