While scientific applications require CCD detectors with maximum quantum efficiency, very low noise, high dynamic range and linear response to light, astro-photographers rather appreciate anti-blooming to be able to acquire wide-field images with bright stars without blooming spikes and electronic shutter for very short exposures of Moon and planets. Some astro-photographers also prefer single-shot-color cameras not to bother with filters and combination of resulting images from individual color images. New CCD cameras G2-2000 and G2-4000 provide all these features.

Both camera models, based on Kodak KAI CCDs, share important features with the Kodak KAF CCD based G2-0402, G2-1600 and G2-3200 models intended for scientific applications and narrow-band imaging:

• Compact camera head, small and lightweight enough to be attached even to small telescopes.

• Hight-quality, very low-noise electronics for images with maximum S/N and without artificial gradients and other artifacts.

• Efficient and precisely regulated CCD chip cooling up to 50 °C below ambient temperature.

• Integrated all-in-one design with USB and power connectors directly on the camera head.

• Integrated shutter not to bother with covering the telescope when taking dark frames.

• Integrated filter wheel for standard filters to take (L)RGB or narrow-band images.

• Single-voltage power supply enabling operation from 12V battery or “brick” adapter.

• Fast image transfer over High-speed USB connection to the host PC with Plug and Play driver installation.

• Wide choice of various adapters for all common standards of telescopes, coma-correctors, focal reducers or field flatteners, microscopes, photographic lenses etc.

• Robust construction to sustain every-day usage.

• Rich software support.

Other features are especially important for astro-photographes:

• Strong anti-blooming gates ensure proper images of bright stars in the field of view without blooming spikes.

• Electronic shuttering allows very short exposures of bright objects like Moon and the planets.

• Fast windowing allows reading of arbitrary detector sub-frame faster than in the case of KAF CCD detectors.

• Single-shot color camera variants with advanced multi-pass color (Bayer) pattern demosaicing in software.

G2 CCD series with Kodak KAI CCDs include four models:

G2CCD 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 astronomical slow-scan, cooled cameras usually require computer for operation control, image download, processing and storage etc. To operate G2 CCD camera, you need a computer which:

1. Is compatible with a PC standard.

2. Runs a modern 32-bit Windows operating system.

   Remark:

   G2 camera USB driver is designed for Windows 2000 and better operating systems (e.g. Windows XP). Older 16/32-bit systems, like Windows 95/98 and Windows Me, are not supported. G2 CCD cameras cannot properly operate with such operating systems.

3. Provides at last one free USB port.

   Remark:

   The current series of G2CCD 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.

G2 CCD Cameras Technical Specifications

CCD Chip

G2-2000 and G2-4000 cameras use low noise Kodak KAI Interline Transfer CCD detectors. Advanced manufacturing techniques like transparent electrodes and microlensing ensure maximum quantum efficiency of monochrome models 55%. The inherent dark current as well as read noise is very low, so the resulting image S/N ratio is very good.

Model G2-2000 and G2-2000C

G2-2000 model uses 2 MPx Kodak KAI-2020 CCD chip.

Model G2-4000 and G2-4000C

G2-4000 model uses 4 MPx Kodak KAI-4022 CCD chip.

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 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.

• ULN (ultra 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 G2-2000

Model G2-4000

Notes:

1. Binning can be combined independently on both axes

2. Download times are valid for USB 2.0 host and may vary depending on host PC. Times stated here were measured on 1.5 GHz Pentium M based laptop computer.

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

Chip Cooling

Regulated two-stage thermo-electric chip cooling up to 50 °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. Water-assisted cooling is available for all G2CCD cameras. Contact the manufacturer for details.

3. 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.

4. One 50 mm fan is used in G2 cameras revision 3 and higher. Older revisions used two 40mm fans.

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 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. G2 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 114 × 114 × 77 mm (approx. 4.5 × 4.5 × 3 inches). The head is CNC-machined from high-quality aluminum and black anodized. The head itself contains USB-B (device) connector 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. Integrated filter wheel contains 5 positions for standard 1.25" threaded filter cells. A variant of filter wheel with 6 positions for 1" “glass-only” filters is also available.

Slightly slimmer variant of the camera head without internal filter wheel is available. The head dimensions are 114 × 114 × 65 mm (approx. 4.5 × 4.5 × 2.5 inches). This variant allows attaching of external filter wheel with 10 or 12 positions for D36 mm or D31 mm filters.

Notes:

1. Shortest exposure time 100 ms is available on G2 cameras revision 3 and higher. Shortest exposure time of older revisions was 175 ms.

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.

Drivers for third-party software are also available (e.g. MaxIm DL, AstroArt, etc.). Visit the “download” portion of the manufacturer 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). And the number of necessary parameters lead to splitting of the “Guiding” tab in the SIPS into two separate tabs. The first one is called “Guiding setup” and it summarizes all parameters necessary for proper autoguiding setup.

The second tab called “Guiding” thereafter 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.

This tab also graphically displays 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 tab. The log can by anytime saved to log file.

Advanced reconstruction of color information of single-shot-color cameras

Color CCD detectors have red, green and blue filters applied directly on individual pixels (so-called Bayer mask).

Every pixel registers light of particular color only (red, green or blue). But color image should contain all three colors for every pixel. So it is necessary to calculate missing information from values of neighboring pixels.

There are many ways how to calculate missing color values—from simple extending of colors to neighboring pixels (this method leads to coarse images with visible color errors) to methods based on bi-linear or bi-cubic interpolation to even more advanced multi-pass methods etc.

Bi-linear interpolation provides significantly better results than simple extending of color information to neighboring pixels and still it is fast enough. But if the telescope/lens resolution is close to the size of individual pixels, color artifacts appear close to fine details, as demonstrated by the image above.

Multi-pass algorithm is significantly slower compared to single-pass bi-linear interpolation, but the resulting image is much better, especially in fine details. This method allows using of color camera resolution to its limits.

SIPS offers choosing of color image interpolation method in both “Image Transform” and “New Image Transform” tools. For fast image previews or if the smallest details are significantly bigger than is the pixel size (be it due to seeing or resolution of the used telescope/lens) the fast bi-linear interpolation is good enough. But the best results can be achieved using multi-pass method.

Shipping and Packaging

G2 CCD cameras are supplied in the foam-filled, hard carrying case containing:

• Camera body with a user-chosen telescope adapter. The standard 2" barrel adapter is included by default. If ordered, the filter wheel is already mounted inside the camera head and filters are threaded into place (if ordered).

• 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 or USB Flash Drive with camera drivers, SIPS software package with electronic documentation and PDF version of User's Manual.

• A printed copy of User's Manual.

Image Gallery

Example images captured with G2 KAI cameras.

All images published with permission of their respective authors.