Cameras
At the observatory, there is a range of dedicated astro cameras available with different sensor-sizes and qualifications. From the full-frame Moravian C3-61000Pro, all the way to the tiny ASI224MC for planetary work. All cameras are CMOS-based. For the monochrome cameras, filter sets in different sizes are available from both Astrodon and Chroma, to properly cover the sensors of different sizes.
Moravian C3-61000Pro
The Sony IMX455 backside illuminated CMOS-sensor is a very popular full-frame sensor. It has a pixel-size of 3.8 µm and impressive 61MP resolution. Moravian has built this sensor in its C3 line of cameras and refers to it as the C3-61000. Moravian cameras stand out through their top-notch build quality and focus on reliability. The whole body and filter wheel is machined from aluminium. The C3-cameras have a mechanical shutter to keep dust away from the sensor, and to take dark-frames without having to cover the telescope. The cooling mechanism with two cooling fans is pretty strong and capable of cooling the sensor to 40°C below ambient.
The sensor of the C3-61000 has a true 16-bit readout and a large full-well depth of 51ke. This gives the system an impressive 14 stops dynamic range. The camera is available in two versions, the regular and the ‘Pro’ version. The only difference is the reliability of the sensor. The Pro version includes the so-called ‘industrial grade’ sensor, classified for more than 300h of use per year. The mechanical shutter, industrial grade sensor, and general high build quality make it a great camera for a remote observatory, where reliability is so important
Specifications
Resolution: 9576*6388 pixels (61 Megapixels)
Sensor-size: 36 x 24mm; 43.3mm diagonal
Quantum Efficiency: 91%
Full well capacity: 51.4ke; ADC: true 16-bit
Gain range: 0-4030; High Conversion Gain: 2750
Power consumption: 8W (no cooling) - 47W (max cooling)
Dimensions (without filterwheel): 154 x 154 x 65 mm
Weight (incl filterwheel “M”): 2.5 kg
Mechanical Shutter
The C3-61000 has a mechanical shutter, which protects the sensor from dust. Also, with the shutter closed, dark frames can be collected without having to cover the telescope. The camera connector comes with an integrated tilt adjustment mechanism. It is available in many configurations, allowing it to fit many imaging trains. The example here is fitted with an M68 fitting.
Integrated Filterwheel
The C3 monochrome cameras come with an integrated filterwheel. For filters up to 36mm in diameter, this can be integrated in the square housing of the camera. For larger filters, the filterwheel is contained in a round housing that is screwed onto the camera. A small dedicated RJ-11 based cable ensures powering of the wheel and communication between the wheel and the camera.
Chroma Filters
For the full frame sensor, the filterwheel is equipped with a set of seven round 50mm unmounted Chroma filters. They include the Luminance, Red, Green and Blue broadband filters, as well as H-alpha, Oxygen-III and Sulfur-II narrowband filters with 3nm bandwidth. The filters are placed at the back, facing the camera. They are held in place with three little screws, without any filter-masks.
Centerplate
The C3 camera system allows for quite some customisations. Differently sized (semi)integrated filterwheels, different cooling options, optional ethernet connectivity, etc. One purely cosmetic option is the choice of color for the camera center plate. Default is black, but you can opt for a blue or red option. Here blue is chosen to match the CDK14 telescope it will be attached to.
Build Quality
The build quality of the Moravian cameras is top-notch. The whole body is made of machined aluminium. This gives a lot of structural strength to the body, which gives some interesting options for connecting add-ons. The top of the camera has four M4 holes and two 1/4” holes. A vixen-style dovetail is one of the accessories available to make use of this connectivity.
Balancing weights
Large filterwheels like those on full-frame systems, create a challenge for balancing. Their asymmetric weight distribution makes balancing the ‘Z-axis’ difficult, especially when the camera can rotate. Therefore the camera is equipped with four 200g balancing weights screwed into the 1/4” connection points on the camera. The weight distribution is now always the same, no matter the rotation of the camera..
ZWO ASI6200MM-Pro
Also the ZWO ASI6200MM Pro camera is built around the Sony IMX455 backside illuminated CMOS-sensor. A full-frame sensor with a pixel-size of 3.8 µm. The resolution is an impressive 61MP. This sensor is a popular choice in the astrophotography world, especially when paired with telescopes that support full-frame sensor sizes.
Most cameras have a 16-bit readout, but often this is an upsampled 12- or 14-bit signal from the sensor. The ASI6200MM has a true 16-bit sensor readout, providing a lot more tonal information especially in the darker part of the image, the part most interesting for astrophotography. Coupled with an exceptionally high Quantum Efficiency of >90% and a pretty large full-well depth of 51.4ke, the camera is able to record 14 stops of dynamic range. The sensor has a so-called dual-gain setting, which switches hardware circuitry on-chip. This results in a drop in read-noise at gain 100 while maintaining the same 14 stop dynamic range as with gain 0.
Specifications
Resolution: 9576*6388 pixels (61 Megapixels)
Sensor-size: 36 x 24mm; 43.3mm diagonal
Quantum Efficiency: 91%
Full well capacity: 51.4ke
ADC: true 16-bit
Interface: USB3 (image download) and 2 x USB2 hub
Camera size: 90mm diameter, 700g
Field of View
The sensor of the ASI6200 is a full-frame size of 36x24mm, or the traditional film-size. The bigger the sensor, the bigger the Field of View. Coupled with the TOA-130, the horizontal FoV is 2.07°, twice as big as the 1.01° of the TOA-130/ASI1600 combination. The 43.3mm diagonal means that regular 1.25” filters are too small and that 50mm diagonal round or square filters are required. Also, the image circle of the telescope/flattener should be large enough to capture full frame. The 67-FL flattener on the TOA-130 projects an image circle of 90mm, more than large enough for the ASI6200.
Sensor: 61 Megapixels
Each image of the ASI6200 contains 61MP of information, and that is a lot. The file-sizes are significant, with roughly 100Mb/frame. Transferring these files from camera to acquisition computer takes significant effort. For a local connection, transfer time is less than 1 sec. When transferring over WiFi, this time increases to 20 sec, significantly longer than the 6 sec of the ASI1600. Storage is another point of interest, but storage gets cheaper every year. One can use the camera in bin2 or bin3 mode, which reduces resolution and file-size by a factor of 4 or 8 respectively.
Cooling
In ZWO-nomenclature, ‘Pro’ indicates ‘Cooled’. The sensor can be cooled to about 35°C below ambient temperature. Cooling reduces the dark-current, a component of the read noise. The dark current is very low in this camera. At -20°C it is 0.0006 e-/s/px. This is 10 times lower than the ASI1600 at the same temperature. Cooling further will add little to the noise reduction. Standardising temperature across sessions has the advantage that only one set of bias/dark frames is needed. -15°C is a good standard for year-round imaging. For cooling, 12V DC power needs to be supplied to the camera.
QHYCCD QHY268c
From the company QHYCCD is this QHY268c APS-C sized colour camera. It is built around the Sony IMX571 sensor and available in a colour and monochrome version. The sensor has a resolution of 26 MP with individual pixels measuring 3.8 µm. This modern 16-bit sensor has a dual-gain design. At gain 26 the sensor gives an extra boost in dynamic range up to 13.5, the same as at gain 0. So there is not much reason to use any other setting. Noise levels are very low and sensor temperature can be cooled to about 35 degrees below ambient.
The sensor in this camera can also be found in astro cameras from other brands. The ZWO ASI2600 for example is very similar to the QHY268. Differences are in the electronics. The QHY268 can be used in different shooting modes for different situations. Also the cover glass in the QHY is anti-reflective clear glass to reduce halo-effects. It means that it should be used with a separate IR/UV cut filter. The ZWO has an IR/UV cut filter built in to cover the sensor. Both the monochrome and colour versions of this camera have become very popular astro cameras. The APS-C sensor-size is a good cost/benefit option and fits many optical systems.
For the observatory, the addition of a one-shot-colour camera is a nice addition to the monochrome cameras. Great for imaging fairly bright clusters and galaxies, a nice option for moon photography, and an almost must-have for fast moving objects such as comets.
Specifications
Resolution: 6280*4210 pixels (26 Megapixels)
Sensor-size: 23.5 x 15.7mm; 28.3mm diagonal
Quantum Efficiency: 92%
Full well capacity: 51ke (75ke in extended full well mode)
ADC: true 16-bit
Interface: USB3 (image download) and filterwheel (proprietary)
Camera size: diameter: 90mm, weight: 780g
Filters and Adapters
The sensor of the QHY268c is covered with an anti-reflective cover glass only. So for regular broadband imaging an UV/IR cut filter needs to be added. Here a 2” Astronomik L3 Luminance filter is screwed in the adapter. QHY has its own standard when it comes to spacers and adapters. A proprietary eco-system of spacers of different thickness, different screw connections, camera adapters etc is kept together through a ring of 6 screws. The benefit is that the connection is very strong with no wiggle. The flip side is that owning a QHY camera probably means some extra investment in the adapter system. On the above image the adapter set for Canon EF mount is mounted.
Sensor: 26 Megapixels
The sensor is APS-C sized and contains pixels with a very common size of 3.76 µm. In total this means that the camera produces 26 Megapixel images. Each file is about 52MB in size. The sensor can be read in one of four modes. Mode 0 is the most common one and referred to as the photographic mode. Mode 1 is high gain mode which gives more signal but at the cost of noise. Mode 2 is the extended full well mode which gives more dynamic range, but also at the cost of noise. Mode 3 is a modification of the extended full well mode, with a slight reduction of the noise.
Connectivity
The QHY268c is 12V DC powered. An special connection is at the back of the camera and a fitting special cable comes in the box. It allows the power cable to be screwed securely in its socket. Downloading the images to the computer is very fast (fraction of a second) and runs through a USB3 connection using the classical clunky USB-B connector. The filterwheel can also be connected to the camera, but QHY uses here a proprietary connector. This means that only a QHY filterwheel can be connected to this camera. When using a filterwheel from another brand, it needs to be connected to the computer. In contrast to the ZWO cameras, there is no USB hub on the camera.
ZWO ASI533MM-Pro
The ASI533MM Pro camera is the mono-version of the very successful ASI533MC Pro. It houses a 9 Megapixel square backside illuminated sensor with dual-gain technology. It essentially has no dark current, does not suffer from amp-glow and generally produces very clean images. The pixel-size of 3.76 is the same as many other cameras currently on the market.
Being a Pro-version it has cooling built in. The sensor can be cooled down to about 35 ºC below temperature, slightly less powerful than the ASI1600. The camera can use the same 1.25” mounted filters as used previously for the ASI1600MM Pro.
The connections are the same as other ZWO cameras, with a USB-3 connection for image download and a dual USB-2 hub. The camera requires 12V DC power at all times. Previous models could connect with USB-3 only and used the power for cooling. The ASI533MM needs power connected for the USB connection to be established.
Specifications
Sensor: Sony IMX533CLK-D
Resolution: 3008 × 3008 pixels (9Megapixels)
Sensor-size: 11.3 x 11.3mm; 15.97mm diagonal
Quantum Efficiency: 91%
Full well capacity: 50ke
ADC: 14-bit
Interface: USB3 (image download) and 2 x USB2 hub
Camera size: 78mm diameter, weight 470g
Connections
The connection layout on most of the cooled ZWO cameras is very similar. The main connection is a USB3 port. This allows for very fast download speeds of images into the acquisition computer. Unfortunately it still uses the clunky B-type plug. A USB-C connection would be more convenient. The choice for B-type does eliminate the risk to mistakenly use one of the other two type-A plugs, which are USB2. These connectors are actually a small USB-hub. Typical devices that connect through this hub are the filterwheel and (if used) a guide-camera.
Next to the USB-ports is the 12V DC connector. This separate power supply is needed at all times and if cooling is on, can draw quite a bit of power.
Square Sensor
The sensor in the ASI533MM Pro has a square format. For galaxies, clusters etc, this makes for easy composition. But it might not be to everyones taste. The 11.31 mm length/width and 9 Megapixel is not very large. Many deep sky objects fit very well in the frame when combined with the 1000mm TOA-130 telescope. But for larger nebulae the ASI6200MM Pro is a better fit. The sensor has dual gain and essentially no dark current and/or amp glow and a very low noise-level. Pixel-size is 3.76 µm, similar to many other astrocamera’s. With the 1000mm TOA-130 telescope the pixel-scale is 0.78 arcsec/px and for the FSQ-106 it is 1.48 arcsec/px.
EOS-EF mount
With the flattener on the telescope, the back focus distance from the flattener to the sensor-plane is extremely critical. Finding the proper adapters can be a tedious job, and many people have custom adapters made for their equipment. At the observatory, if possible, the imaging train is standardized on the EOS-EF mount. ZWO often designs a combination of camera + filterwheel + EOS-camera mount that is exactly the flange distance of the EOS-EF mount of 44mm. On the telescope side, Takahashi makes adapters that result in an EOS-EF lens mount at the right distance. Using the EOS-EF mount makes it very easy to attach/detach the camera, while the connection itself is very solid, with little to no play.
ZWO ASI1600MM-Pro
The ASI1600 camera is used by many around the world and comes in different versions. At the heart of all is a Micro-Four-Thirds CMOS sensor from Panasonic. This is the same sensor found in for example the Panasonic GH-4 camera, but then without the colour-filter array. It has a resolution of 16MP and a pixel-size of 3.8 µm.
Being a Pro-version it has cooling built in. The sensor can be cooled down to about 40 ºC below temperature. The camera is monochrome, so filters are required to make color images. See below for more details on filters and filter wheel.
The camera downloads data through a USB-3 connection and acts as a USB-2 hub for the filterwheel. Power for the cooling is applied through a 12V DC connection.
Specifications
Sensor: Panasonic MN34230
Resolution: 4656×3520 pixels (16Megapixels)
Sensor-size: 17.6 x 13.3mm; 21.9mm diagonal
Quantum Efficiency: 60%
Full well capacity: 20ke
ADC: 12-bit
Interface: USB3 (image download) and 2 x USB2 hub
Camera size: 78mm diameter, weight 410g
Filters
The C3-61000Pro, ASI6200 and ASI1600 are monochrome cameras. Filters are needed to make a color image. The basic set consists of a Red, a Green and a Blue filter. Usually best sharpness/contrast is achieved by recording the luminance separately with a luminance filter. All these filters are broad-band filters, as each spans a broad range of wavelengths. For nebulae, great photos can be made using so-called narrow-band filters. These are specific to one specific wavelength, corresponding to a specific energy transition of certain elements in the nebulae that are characteristic for certain astrophysical processes. Typical examples are Hydrogen-alfa, Sulfur-II and Oxygen-III. While designed for one specific wavelength, in reality they always have a (small) bandwidth, for example 7, 5 or 3 nm. The smaller the bandwidth, the better. Because these filters have such small bandwidths, they are very insensitive to light pollution. So they are often a good choice for imaging in/near cities, or when the moon is out.
A filter has a certain thickness and therefore have an effect on focus. If each filter in a set has the same thickness and the same effect on focus, it is called par-focal. Using par-focal filters means that focus is maintained each time another filter is chosen. Due to the refraction within a filter, the thickness of the filter has an effect on the back focus distance. Typically a 3mm thick filter extends the back focus by approximately 1mm. This is important to take into account when planning the imaging train.
Filters come in either round or square shape. Their size is dependent on the sensor-size of the camera. The usual round-filter sizes are 1.25” and 2”. The former works well for all sensors up to micro-four-thirds, like the one in the ASI1600. For APS-C and full-frame sensors such as in the ASI6200, 2” filters are required.
Filters are placed in a filterwheel that is completely sealed off from any environmental light. Rotation of the filters in front of the camera is controlled via software. Best is to use a filterwheel that holds all the filters that you typically use. Opening the wheel and replacing filters is not something you want to do during an imaging session.
Filterwheels
Filterwheels for 8 x 1.25” filters (small one) and 7 x 2” filters (large one). There is a significant difference in both size and weight of these wheels. Notice the EOS-EF adapter on both wheels. Using this standardized mount, camera/filterwheel combinations can be easily exchanged without having to alter the imaging train. The filterwheels are powered through their USB connection. In the case of the ZWO-cameras, the USB cable plugs into the USB-hub on camera, which keeps cable lengths very short.
1.25” Astrodon filters
A set of 7 x 1.25” Astrodon filters. These include the GEN2 E-series LRGB tru-balance filters. Tru-balance means that if you expose all three colours for the same length, the resulting image using 1:1:1 relative weights will be colour-balanced. E-series is designed for modern CCD’s and can best be used for CMOS sensors. Astrodon also has an I-series, designed for older interline CCD sensors. Also included are three 5nm narrowband filters: Ha, SII and OIII. On position 8 there is a blind filter, used when taking dark or bias frames.
2” Chroma filters
For the ASI6200 with its full-frame sensor, a new set of 2” filters was required. In recent years the company Chroma has really established itself as a high-end brand in astrophotography filters. When ordered directly with the company, delivery is typically within a few weeks and feedback on service is very good. The set used here is identical to the set of 1.25” filters, so LRGB, Ha, SII and OIII. But the narrowband filters here have a bandwidth of 3nm. The filters are unmounted, reducing the risk of unwanted reflections in the light-path.
ZWO ASI224MC and ASI290MM
Most of the work here at AstroWorldCreations is about deep sky imaging. But recently some additions were made to the observatory that should allow moon and planetary imaging. Making photographs of planets requires a very different setup.
Planets are much smaller than deep sky objects. So a long focal length and a small sensor work best. Planets are also much brighter, and can do with exposures just a fraction of a second. The easiest way to go about is record a movie and try to get the highest frame-rate you can get. In post-processing the software can help selecting the best frames and stack them to the final image.
The cameras available here for planetary work are a ZWO ASI224MC colour camera and a ZWO ASI290MM monochrome camera. The colour camera seemed so far the easiest option and resulted in the first images of Saturn and Jupiter. The monochrome setup with filterwheel turned out to be very tricky to focus. Perhaps something wrong with the back focus distance or simple user error. Anyway, it will probably take a while before you will see some decent images of planets showing up on AstroWorldCreations, but stay tuned.
Specifications
ASI290MM
ASI224MC
Sensor: Sony IMX290
Res.: 1936×1096 pixels (2.1MP)
Pixel-size: 2.9 µm
Sensor-size: 5.6 x 3.2mml
Frame rate: 170 FPS
ADC: 12-bit
Interface: USB3
Diameter: 62mm, weight 120g
Sensor: Sony IMX224
Res.: 1304×976 pixels (1.2MP)
Pixel-size: 3.75 µm
Sensor-size: 14.8 x 3.6mm
Frame rate: 150 FPS
ADC: 12-bit
Interface: USB3
Diameter: 62mm, weight 100g
Connections
Even these small cameras have full USB-3 connections for high speed download of data. The 1-2 MP sensors, in combination with USB3 connection allow for maximum frame rates of full resolution of 150-170 fps. This is in sharp contrast to the 15 fps that the ASI1600 can produce. Since there is no cooling, there is no 12V DC connector.
1.2-2.1 Megapixels
Small cameras with very small sensors. With 1.2 MP for the ASI224 and 2.1MP for the ASI290 (photo), these will not produce images for printing on any reasonable size. The resolution is well enough for planetary imaging though, where often even a Region of Interest (ROI) of 640 x 480 pixels is used.
Small size
Both the ASI224MC and ASI290MM are extremely small in size, when compared to the large cooled cameras. The ASI290MM is also available in a mini-version with a diameter of 36mm and a weight of only 60g. Technically identical to the regular one, but in a different form factor that makes it well suited as guide-camera.