G3 cameras can contain OnSemi KAF Full-Frame CCD detectors as well as KAI Interline Transfer ones.

• OnSemi KAF CCDs without ABG (Anti-Blooming Gate) offer linear response to light are suitable for scientific applications. Large area detectors with large pixels fit well to long focal length of professional observatory telescopes. Large pixels enhance image dynamic range.

• OnSemi KAF CCDs with ABG can be used both for research applications and also for astrophotography. Anti-blooming ensures round shapes of bright stars, while the Full-Frame architecture provide clean and uniform frames without artifacts.

• OnSemi KAI detectors with ABG and electronic shutter could be used for astrophotography. Anti-blooming ensures round shapes of bright stars, which cannot be avoided especially on wide field images.

No matter if your target is reliable scientific data or beautiful images of deep-sky objects, G3 cameras are able to provide both.

G3 Camera Overview

G3 camera head is designed to be easily used with a set of accessories to fulfill various observing needs. Camera head itself is manufactured in two different variants:

• Camera with internal filter wheel for five 2" or D50 mm unmounted filters.

• Camera with control port for external filter wheel. This model allows attachment of the external filter wheel for seven 2" or D50 mm unmounted filters.

Camera head and numerous accessories comprise imaging system, capable to be tailored for many applications.

1. G3 camera head with internal filter wheel

2. G3 camera head capable to control External Filter Wheel

3. External Filter Wheel “S” size (7 positions)

4. External Filter Wheel “L” size (9 or 7 positions)

5. G0 Guider camera

6. G1 Guider camera

7. Off-Axis Guider with M68 × 1 thread

8. Spacer compensating IFW and EFW back focal distance

9. 1.75” dovetail rail for G3 camera head

10. Gx Camera Ethernet Adapter (x86 CPU)

11. Gx Camera Ethernet Adapter (ARM CPU)

    Remark:

    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.

12. 5-positions internal filter wheel for 2”/D50 mm filters

13. 7-positions external filter wheel “S” for 2”/D50 mm filters

14. 9-positions external filter wheel “L” for 2”/D50 mm filters

15. 7-positions external filter wheel “L” for 50 × 50 mm filters

16. 2-inch barrel adapter

17. T-thread (M42 × 0.75) adapter

18. Canon EOS bayonet adapter for Canon compatible lenses

19. Nikon bayonet adapter for Nikon compatible lenses

G3 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 G3 camera, you need a computer which:

• Is compatible with a PC standard.

• Runs a modern 32-bit or 64-bit Windows operating system.

  Remark:

  Drivers for 32-bit and 64-bit Linux systems are also provided, but camera control and image processing software, supplied with the camera, requires Windows operating system.

• Provides at last one free USB port.

  Remark:

  The current series of G3 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.

• Alternatively it is possible to use the Gx Camera Ethernet Adapter. This device can connect up to four Gx cameras of any type (not only G3, but also G0, G1, G2 and G4) and offers 1 Gbps and 10/100 Mbps Ethernet interface for direct connection to the host PC. Because the PC then uses TCP/IP protocol to communicate with the cameras, it is possible to insert e.g. WiFi bridge or other networking device to the communication path.

G3 Camera Models

G3 series contains the following camera models:

G3 CCD Cameras Technical Specifications

CCD chip

G3 CCD cameras use OnSemi KAF Full Frame CCD detectors or KAI Interline transfer CCD detectors with ABG and electronics shutter. Advanced manufacturing technologies like transparent electrodes and microlenses on the chip surface ensure high quantum efficiency. The inherent dark current of these detectors is very low compared to other scientific-grade CCDs, so the resulting image S/N ratio is very good.

Model G3-1000

G3-1000 model uses 1 MPx OnSemi KAF-1001E CCD.

Model G3-6300

G3-6300 model uses 6 MPx OnSemi KAF-6303E CCD.

Model G3-16200

G3-16200 uses 16 MPx OnSemi KAF-16200 CCD with APS-H format.

Model G3-11000

G3-11000 uses 11 MPx OnSemi KAI-11002 Class 1 or 2 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 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.

Gx Camera Ethernet Adapter device allows connection of up to four Gx cameras of any type through Ethernet interface and TCP/IP network. Because TCP/IP protocol can be routed, the distance between camera and host PC can be virtually unlimited.

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 G3-1000

Model G3-6300

Model G3-16200

Model G3-11000

Notes:

1. Binning can be combined independently on both axes

2. LN read noise depends on the CCD chip itself. If the read noise of the particular chip is 11.5 e^- RMS, the system read noise is also 11.5 e^- RMS.

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

Chip Cooling

Regulated thermoelectric cooling is capable to cool the CCD chip from 45 to 50 °C below ambient temperature, depending on the camera type. The Peltier hot side is cooled by a fans. The CCD chip temperature is regulated with ±0.1 °C precision. High temperature drop and precision regulation ensure very low dark current for long exposures and allow proper image calibration.

G3 cameras are available in two variants, differing in the cooling performance:

• Standard cooling cameras achieve temperature difference up to 45 °C Under environment temperature.

• Enhanced cooling cameras can regulate temperature up to 50 °C under environment temperature. Compared to standard variant, enhanced cooling cameras are somewhat bulkier due to bigger heat sink, slightly heavier and somewhat noisier because of more powerful fans.

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.

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.

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 12 V.

3. G3 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 × 2.6 inches). A variant with internal filter wheel is thicker and measures 77.5 mm (approx. 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. Optional integrated filter wheel contains 5 positions for standard 2" threaded filter cells with M48 × 0.75 thread or up to 50.8 mm “glass-only” filters.

Regardless if the camera has standard or enhanced cooling or if it is equipped with internal filter wheel or not, the front view dimensions are the same. Also mounting adapter holes are the same, so both camera variants are compatible with the same set of telescope/lens adapters.

The only different dimension is the camera thickness. Enhanced cooling requires thicker camera back shell.

Variants without and with internal filter wheel have different front shell thickness, which brings different Back Focal Distance, but mechanical spacers, compensating for different BFD are available (see the system diagram in the “G3 Camera Overview” sub-chapter above).

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

Various telescope and lens adapters for the G3 cameras are offered. Users can choose any adapter according to their needs and another adapters can be ordered separately.

It is possible to choose from the following telescope/lens adapters:

If the mounting standard defines also back focal distance (distance from adapter front plane to detector), the particular adapter is constructed to preserve defined distance (for instance T-thread defines back focal distance to 55 mm, but certain distance is defined also for Pentax (Praktica) thread, for Canon EOS and Nikon bayonets etc.).

Adapters are attached to the camera body using four M3 (3 mm metric) screws. These threaded holes are placed on the corners of 44 mm square. Custom adapters can be made upon request.

External Filter Wheels

When there is no filter wheel inside the camera head, all electronics and firmware, intended to control it, stays idle. These components can be utilized to control external filter wheel with only little changes. Also the camera front shell can be manufactured thinner, the space for filter wheel is superfluous.

External filter wheels are described in detail here.

Off-Axis Guider adapter

The G3 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 G3 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 G3 OAG.

The G3 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 G3 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.

Attaching camera head to telescope mount

G3 cameras are equipped with two “tripod” 0.250-20UNC threads on the top side of the camera head. This thread can be used to attach 1.75 inch “dovetail bar” (Vixen standard). It is then possible to attach the camera head, e.g. equipped with photographic lens, directly to various telescope mounts supporting this standard.

Spare desiccant containers

The G3 cameras are supplied with silicagel container, intended to dry the CCD cold chamber. This container can be unscrewed and desiccant inside can be dried in the owen (see the camera User's Manual).

Container shipped with the camera by default does not exceed the camera head outline. It is equipped with a slot for tool (of for just a coin), allowing releasing and also tightening of the container. Containers intended for enhanced cooling cameras are prolonged as the camera thickness is greater in the case of this variant.

It is possible to order spare container, which makes desiccant replacement easier and faster. It is possible to dry the spare container with silicagel and then only to replace it on the camera. Spare container is supplied including the air-tight cap.

Spare container can be supplied also in variant, allowing manipulation without tools. But this container is longer and exceeds camera outline. If the space behind the camera is not critical, this container can make desiccant exchange even easier.

Camera head color variants

Camera head is available in several color variants of the center plate. Visit manufacturer's web pages for current offering.

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.

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 below left.

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

G3 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.

• USB Flash Drive or CD-ROM 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 G3 cameras.

All images published with permission of their respective authors.