Noise associated with warm sensor temperatures during long-exposure shots usually has an effect of turning a supposedly black region into noisy and grainy one. In a typical DSLR, the imaging sensor heats up during exposure, causing its temperature to reach up to 10 deg C above ambient (with sensor temperatures reaching up to 35 to 40 deg C), further increasing the thermal noise. By cooling down the imaging sensor, it is possible to eliminate or somehow minimize this thermal noise.
Important: This project is a work-in-progress. Learn about the most recent modification attempts here. Links to other related prototypes are listed at the end of this article.
In this project, I will describe how I modified my Canon 450D DSLR to become a dedicated astronomical camera, with all functions intact including the auto-focus capabilities, and thus, may still be used for non-astronomical purposes.
Filter modified (Baader BCF) and Peltier-cooled Canon 450D
Part of the modification is the replacement of the camera’s stock (built-in) filter with a Baader BCF. The filter allows greater sensitivity to H-alpha wavelengths emitted by most deep-sky objects, while at the same time eliminate unwanted UV and other IR wavelengths. This filter is necessary for any system that uses lenses in the optical train.
Stock filter (left) replaced with a Baader BCF (right) to improve the camera’s sensitivity to H-alpha wavelengths
In my first prototype of a cooled DSLR camera, I used a Peltier module to directly cool down a Canon 450D’s imaging sensor, through cold plate (or cold finger) approach. Through this method, I was able to lower the temperature to up to 21 deg C below ambient, even when the camera is operating. To avoid issues related to condensation, the camera was equipped with nichrome wires to maintain the front of the sensor a few degrees above ambient (same principle in a dew heater).
To effectively dissipate heat buildup on the hot side of the Peltier module, I used an aluminum heat sink with a fan. I specifically used a magnetically-levitated fan (Sunon) mounted on rubber pads for this purpose to minimize vibration.
Below are some photos of the project during construction and detailed descriptions of some of the key steps in the modification.
The camera’s imaging sensor, a CMOS (left)
Disassembling the CMOS’s cell/holder
Carefully removing the stock filter with a sharp blade
Installing the Nichrome heater and a thermometer’s sensor
Shown here is a 1.8 mm gap between the imaging sensor and its circuit board, where the cold plate will be placed
Reassembling the imaging cell. The 4 wires visible on the left are for the Nichrome heater and the thermometer’s sensor.
Cold plate fashioned from a solid copper plate
A metal grinder was very useful in achieving the plate’s correct thickness, which is a little thinner than the 1.8 mm gap
Precise measurement using a caliper is necessary to avoid any strain on the sensor and its circuit board
The cold plate (left) with the thermometer sensor attached. Electrical tape on the back side of the cold plate provides electrical insulation.
Thermal paste promotes effective heat transfer between surfaces. Thermal paste is applied between (1) the sensor and the cold plate, (2) the cold plate and the cold side of the Peltier module, and (3) the heat sink and the hot side of the Peltier module. Note that you only need to apply a thin layer of thermal paste (just to fill the gaps and imperfections on the contact surfaces, as applying too much thermal paste will do more harm than good). Also, you must apply ample pressure (using clamps) between contact surfaces in order to squeeze out excess thermal paste and promote heat transfer through conduction, with plates in direct contact with each other and all remaining gaps filled with thermal paste instead of air.
The L-shaped cold plate rests on the backside of the CMOS sensor and is secured in place by 2 screws mounted directly onto the side of the camera.
Thermal insulation is achieved by using mounting tapes and aluminum tapes. Effective thermal insulation is necessary to achieve lower system temperatures.
Side view of the camera showing the cold plate attached firmly on its sides using 2 screws
Another view of the camera showing the cold plate. Notice that the camera operates perfectly after the modification.
Connectors are soldered on to the wires leading to the 2 thermometer sensors and the nichrome heating element
Shown here is a 40 mm by 40 mm Peltier module used in the modification
An aluminum heat sink is used to dissipate heat from the Peltier module’s hot side. A DB25 female connector is used to connect the camera to an external controller box.
An image showing how the components are connected to the DB25F connector
Thermal paste applied onto both sides of the Peltier module. Note that you only need to apply a thin layer of thermal paste (just to fill the gaps and imperfections on the contact surfaces, as applying too much thermal paste will do more harm than good). Also, you must apply ample pressure (using clamps) between contact surfaces in order to squeeze out excess thermal paste and promote heat transfer through conduction, with plates in direct contact with each other and all remaining gaps filled with thermal paste instead of air.
Aluminum (anodized) heat sink and its enclosure/case
60 mm magnetically-levitated fan (Sunon) used to minimize vibration
Initial test showing a recorded sub-zero temperature and the formation of ice on the cold plate
A fully-assembled filter-modified (Baader BCF) Peltier-cooled camera
Modified Canon 450D DSLR. The camera may still be used with any Canon DSLR lens.
All functions of the camera remain intact including auto-focus, and thus, may still be used for non-astronomical purposes.
A sample outdoor shot (custom white balance)
The screenshot shows dark frames (images taken in complete darkness, with the lens cover/cap on) taken with and without cooling (left and right, respectively) at 16 minutes exposure, ISO 1600 (ambient 30 deg C, sensor temperature: -4 deg C). More test shots will be posted soon.
This is still a work-in-progress. Results of field-tests conducted recently and actual shots taken with the camera will be discussed in my future posts. Clear skies!
To view other my other DSLR modification projects, follow the links below:
August 2014 Modified Canon 450D DSLR for Astro-imaging (improved sealed chamber prototype)
March 2014 Modified Canon 450D DSLR for Astro-imaging (sealed chamber prototype)
February 2014 Modified Canon 1000D DSLR (Baader BCF filter replacement)
December 2013 Modified Canon 450D DSLR for Astro-imaging (custom-fabricated lens mount)
November 2013 Modified Canon 450D DSLR for Astro-imaging (sealed chamber prototype)
February 2013 Modified Canon 450D DSLR for Astro-imaging
For DIY astronomy projects useful for astrophotography, click here.
For tutorials on how to get started with astrophotography, click here.
To visit my astrophoto gallery, click here.
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© Anthony Urbano (Manila, Philippines)