Introduction
We previously reported an experiment to case-cool a ZWO ASI 178MC 14 bit OSC CMOS camera. That experiment involved a Yodoit K6 Portable Magsafe Magnetic Mobile Phone TEC Cooling LED Radiator costing under £20 on Amazon UK attached to the flat back of the camera by an adhesive metallic disk to which the cooler could attach magnetically.
The current experiment was an attempt to case-cool a Player 1 Mars-C II 12 bit OSC CMOS camera using a similarly attached Magnetic Mobile Phone Radiator, Refrigeration Turbine Phone Cooling Fan that was purchased from Amazon UK for less than £12.
The metal disk is stuck to the back of the camera. However, the central part of the back of the camera is depressed slightly so that the metallic disk only makes contact with the raised part of the camera back towards the edges. Nevertheless, there is significant contact for heat exchange to take place.
The Mars-C II camera does not feature passive cooling which is a feature of some of the larger format Player One cameras such as the Apollo-M/C, Apollo-M Mini, Saturn-C SQR, Uranus-C and other models. The inbuilt passive cooling system of these cameras facilitates the transfer of heat from the sensor to the camera back. The Player 1 ACS (Active Cooling System) is a fan cooler that bolts onto the back of the camera, but does not involve TEC cooling. Player One states that their ACS does not work with cameras not supporting passive cooling. That makes this TEC plus fan cooler system employed in this experiment an important investigation.
The cooler is held magnetically to the back of the camera by the adhesive disk. It would be possible to place a thermal pad in the recessed area behind the metallic disk to facilitate heat transfer from the back of the camera. We did not employ a thermal pad. Player One employs such a thermal pad in their ACS.
When powered up by means of a USB-C connector and a USB lead to a mains/USB 5v adapter coloured LEDs illuminate the cooler with cycling colour displays.
Capturing long exposure, 16 bit dark images at different camera temperatures
Screenshot of AstroDMx Capture capturing 20s exposures at 500 Gain at 28 degrees C
Screenshot of AstroDMx Capture capturing 20s exposures at 500 Gain at 18.1 degrees C
There was considerably more noise when the camera was at 28 degrees C which it warmed up to over time after the camera was turned on.
A dark image captured at 28 degrees C
A dark image captured at 18.1 degrees C
Both images were stretched by an identical amount to reveal the noise that was present.
Measuring rates of temperature change in the case-cooling setup
The camera was connected to AstroDMx Capture and was set to 16 bit 20s dark exposures at Gain 500. AstroDMx Capture was set to refresh the display of the camera temperature every 5 seconds. The temperature was recorded at intervals until a maximum value was approached. Then the cooling was turned on and the temperature was continued to be recorded until a minimum was reached.
It can be seen that temperature change is a relatively slow process and it took about an hour for the camera to reach a maximum value. Of course, in use, the cooler would be turned on immediately when the camera was connected, so the cooling time would be less than from a camera at its maximum temperature. Cooling time will depend on the ambient temperature when used in the field.
An unknown at the present time is whether the optical window of the camera would eventually become covered in dew and how this would be affected by humidity, or even worse (and possibly dangerous to the camera itself), whether dew would start to form inside the camera, or whether the heat generated by the electronics would prevent this from happening.
Clearly the cooler would be turned on at the outset so that the camera could be cooling down whilst the target is being acquired, the exposure and gain determined, focusing and auto-guiding set up.
We hope to test this case-cooling arrangement in the field in the near future.
Any attempts to reproduce the work done here should be done with caution as there is the caveat that any adverse effects that might affect the camera are at this time unknown. For this reason we are NOT recommending this procedure at this stage.
