The launch of Sony’s A7s this year is remarkable because of it’s very good low light performance and 4K movie mode with it’s Full Frame image sensor.
The A7s 12 megapixels is small compared to other full frame digital cameras but this camera is special to amateur astronomers because of it’s ultra high iso (up to 409,600).
In our tests we found that the noise level is higher than that of the 6D, 5D MkIII but the low light and high iso performance of the A7s is very special.
We disassembled the camera and found that the Sony engineers have made efforts to maintain a smaller body size and that all electronic circuits are integrated onto a main PCB. This is very different from the concept of the Canon DSLR’s where functions are allocated to separate components.
We started the modification of the A7s from two concepts.
First is the re-configuring of the camera system as in the case of the CDS-5D.
Second is to take out the image sensor and move it forward into the new cooling module.
We had a question about the reliability of an extended CMOS connection cable and try to test it.
Before we perform the test, we strengthen the ground circuit and make heat sink and cold block to unite them on Sony’s ground circuit.
With the extended cable the camera works well without any errors in still shot photography and movie mode. One interesting fact is that it shows less noise than the unmodified A7s.
The image sensor of the Astro A7s is moved from the rear to the front of the mechanical shutter. The mechanical shutter can no longer control the exposure.
The Sony A7s has a special function that is not found in the Canon DSLR’s. This is the ”Silent shooting mode”. This function makes it possible to to take images without the mechanical shutter, using only the electronic shutter.
Using this “Silent shooting mode” it is possible to take high shutter speed shoots with the Sony A7s.
We have not maintained Sony’s E mount and have instead applied Canon’s EF mount to the A7s. This allows the Astro A7s to use the Drop-in filter system and telescope adaptors of the CDS series cameras.
It also helped us shorten the development period and keep down the cost of the product.
The cooling module of the A7s is a cylindrical heat sink. This and the detachable EXcooler is the same as on the Astro 6D.
New cooling system.
1. Passive cooling
A7s is a high performance camera supporting 4K movie recording. However, when it is recording or shooting shots, the temperature of the sensor rises to ambient temperature + 7C. This rise in temperature adds noise to the output image. Particularly in the case of low light photography, this internal heat is a major issue to overcome.
We designed a cylindrical heatsink and manufactured it by MCT machine. This heat sink has sufficient radiation areas to provide cooling of -6 to -7C below ambient of the image sensor when powered to TEC without the cooling fan.
Therefore we are achieving a cool down effect of 14C to 15C of the image sensor compared to the unmodified A7s. This helps produce good quality movie and low light images.
Passive cooling is a fan less system and the camera is silent. The current consumption is only about 0.8 amps and this means you can operate the camera for 15 hours continuously with a 12Ah 12v lead sealed battery.
2. Active cooling.
Attach the EXcooler to the bottom side of the heat sink and operate the cooling fan. In this case 8.5v is supplied to TEC and through this ‘active cooling’, the temperature of the image sensor will drop ambient -18C (+2C to -2C).
3.Excooler: the product of ‘Noctua’ company from Austria. They are famous for their silent and high performance cooling fans.
We installed two 40mm notch fans to Excooler and a power circuit board for 18.5V out for TEC. This Excooler is easily attached to the bottom side of the heatsink using one 1/4” screw bolt. In the Excooler we also installed a power supply module for Sony camera operation. This allows the camera to be used without Li-ion battery.
4. Digital Thermometer: for monitoring the temperature of the image sensor. We offer this as a basic accessory with the A7s set.
C. Dark Frame Comparison
Information of the product :
＊Cool down the temperature of CMOS sensor about 18 Celsius degree(±2℃) from that of ambient air.
＊Absolutely high-Quality image in B-shutter use compared with usual DSLR
＊Realtime Monitoring of the cooling temperature by digital thermometer
＊Drop-in filter system
＊Use of high efficiency Thermo electric cooler module.
＊Power: 12V, 2A DC
＊Low Pass Filter Removed.
＊Optimal design by 3D CAD modelling
＊Precision manufacturing by CNC machine
＊Perfect tuning of optical axis of CMOS sensor by 3 point alignment
＊Permanent Anti-dew system applied.
*Detachable Excooler (40mm cooling fan 2pcs & Power supply) included.
*Live-view Focus function alive.
*Mechanical Shutter and Sensor Cleaning function are disabled.