"But one thing became clear to us during the test [of the KL400] at this stay -the course is set for the future. In less than an hour one can record depths which can only be achieved with a CCD over many hours." --Gerald Rhemann
Kepler Cooled sCMOS Cameras
The Kepler Series is a giant step forward in throughput, providing faster digitization, higher speed interfaces, and up to 35 channel readout. Sensorscurrently supported include front and back illuminated sCMOS. Future developments will include interline transfer CCDs and EMCCDs.
- USB3.0 (3 Gbps)
- Optional QSFP (8 Gbps)
- Broadband AR Coated Window - (Transmissivity Curves)
- Air Cooling or Optional Liquid Cooling
- Deep Cooling (up to 45�C below ambient)
- Optional Anti-Dew Technology (ADT)
- LDR and HDR modes
- Small Footprint (4 x 4 x 4.2 in.)
- Reaches operating temperatures in 10 minutes
- Support for up to 35 channels
- View Kepler Overview pdf
For details regarding Kepler Operational Modes and a Signal to Noise Comparison of CCDs versus CMOS, please see the bottom of this page.
Need Extremely Accurate Time Logging? See the Kepler Image Time Stamp.
Kepler Operational Modes
Kepler�s Low Dynamic Range (LDR) mode reads the image once and digitizes it to 12-bits. The user has eight gains to select from in LDR mode. Adjusting the gain affects full well size, dark current growth, and linearity.
The High Dynamic Range (HDR) mode reads the pixels twice, digitizing through different amplifiers with different gains. (Unlike CCDs that only read the charge from each pixel once, CMOS sensors can measure the charge multiple times.) The two images are merged to create a 16 bit image with the linearity of a single image, thus allowing an HDR image to show detail in both low-count and high-count areas of an image. Because of the additional read time, the maximum HDR frame rate is half that of the LDR mode.
The Kepler camera also features a Low Dark Current (LDC) options for both LDR and HDR. When used, the LDC option minimizes dark current at the expense of reduced full well capacity. For short exposures where dark current growth is not a problem, LDC is not generally used. Standard modes (not LDC) provide the highest full well capacity and widest dynamic range. On the other hand LDC mode is very useful for imaging dim objects that require very long exposures where dark current growth can be significant.
The following may be useful in making the decision on which mode is most appropriate:
Choose LDR mode for required frame rate greater than 24 FPS (exposures <42 ms).
Choose HDR mode for a dynamic range greater than 0 � 4095 counts
Choose LDC when your exposures are sufficiently long that dark current growth uses a significant percentage of full well capacity. (Also cool sensor to lowest possible operating temp.)
Do not choose LDC for short exposures.
A Signal to Noise Ratio Comparison: PL16803 CCD vs. KL4040 sCMOS
The ProLine PL16803 has been the de facto standard for astrophotography since its release in 2006, and the Kepler KL4040 continues the tradition of excellence. Both cameras use a 4k x 4k sensor with 9 micron pixels. The difference is the ProLine uses a traditional CCD while the Kepler uses a Scientific CMOS sensor.
The table below is a comparison of the ProLine PL16803 and the Kepler KL4040 cameras, using a low flux value of 1 photon/pixel/second.
|Sensor||KAF-16803 CCD||GS4040 sCMOS|
|Average QE 400-700 nm||50.7%||69.8%|
|Dark Current||0.001 eps||0.15 eps|
|Read Noise||10 e-||3.7 e-|
|Throughput||1 MHz||800 MHz|
|Full Well Capacity||100000 e-||70000 e-|
|Dynamic Range||10000 : 1||18900 : 1|
|SNR 900 sec||19.2||22.5|
|SNR 5 x 180 sec||14.7||21.8|
|SNR 10 x 90 sec||11.9||20.9|
Summary: A Paradigm Shift
It is no surprise that the CCD�s best performance is with a single long exposure. What may be surprising is the Kepler KL4040 has a better signal-to-noise ratio than the PL16803 even with a single long exposure. The signal-to-noise ratio of the KL4040 is better than the PL16803 even when using short exposures that are stacked!
The benefit of taking multiple short exposures is the option to discard a bad exposure ruined by satellite trails, tracking errors, or bad seeing (etc.). Incredible low-noise images are now possible with a single long exposure or many stacked short exposures. The KL4040�s superior performance allows it to be used for a wide range of applications and requirements.