My previous experience with peltier cooling was for a peltier cooled greyscale webcam that I built. I had bought additional peltier devices and fans for cooling a Steve Chambers modified (SC-1) long exposure Philips Vesta webcam that I modified, but I never added the cooling. When I took the Rebel apart for modification, I studied ways to cool the CMOS imaging chip with a peltier device.
Some have tried cooling the Canon Digital Rebel by attaching a peltier device to the metal tripod socket at the base of the camera. This will provide some level of cooling within the camera. The cooling effect will radiate within the plastic camera body through its metal framework and metal shielding. Using this method however, provides very little direct cooling of the CMOS imaging chip.
The ideal method of cooling the CMOS imaging chip is to have the cold finger contact the back of the CMOS chip directly and firmly with thermal transfer paste being used to aid in the heat transfer.
Below is a photo of the the camera with the CMOS imaging chip exposed:
Cooling via the tripod connector has only two metallic connections to the CMOS chip and these are the very thin grounding straps shown in the above photo. The only other physical connections from the CMOS imaging chip to the camera are by three mounting screws, but these are into plastic posts. The grounding straps are part of a thin metallic shield that lays flush with the metallic CMOS assembly frame that surrounds the CMOS chip. There are two copper clips on each side of the CMOS imaging chip that are connected to the CMOS assembly frame. These clips have very minimal contact with the CMOS chip....not good for heat transfer. the minimal contact occurs at the very edge of the copper clips when contact is made to hold the imaging chip in place. Here is a sketch of the contact made:
I studied ways of directly cooling the CMOS imaging chip without making major modifications to the camera body. I considered the following:
Attach a 41mm by 28mm thin piece of aluminum (cold finger) to the back of the CMOS imaging chip using thermal transfer paste and the existing copper hold down clips. Raise the height of the copper clips where they connect tot he CMOS assembly frame with isolating spacers of the same thickness as the aluminum cold finger:
The aluminum cold finger on the back of the imaging chip needs to be extended out the camera and to the peltier device.
I made a model of a cold finger shape out of a piece of purple plastic to see how it would fit in the camera:
This is how it would fit on the CMOS imaging chip (the cold finger would be placed under the copper clips):
With peltier cooler mounted on cold plate:
The procedure would involve:
1. Removing copper hold down clips on CMOS.
2. Applying thermal transfer paste on back of CMOS chip.
3. Placing Part 1 on back of chip.
4. Put isolation spacers of the same thickness as Part 1 between the copper base and CMOS assembly to keep existing hold down pressure the same as pre-modification.
5. Insert Part 2 through slot in base of camera. Slot would need to have been previously drilled out to a size needed for the cold finger runner (5mm wide). This hole needs to be drilled through both the plastic camera body and metal frame.
6. Attach Part 2 to peltier cold side using nylon nuts/bolts/washers and use thermal transfer paste.
7. Place part 2 with peltier device through camera body slot and connect the cold finger runners of Parts 1 and 2 with small screws or nuts/bolts and use thermal transfer paste.
8. Use the camera's tripod socket to bracket the peltier/ fan assembly firmly to the camera body. Maintain clearance for battery cover so that it can fully open.
9. Wrap insulating foam tape around base of cold plate at base of camera. This is how the camera would appear with peltier cooler attached:
I would operate the peltier device at full power using a variable power supply. Using the same peltier device and power supply I have gotten good results with the peltier cooled webcam I built.
Instead of cutting a hole in the camera body as per Method #1 above, the less obtrusive option is to fashion a peltier cooler whose cold plate attaches to the metal tripod connector of the camera. The cooling provided to the CMOS imaging chip could be improved somewhat if the square part of Part 1 in Method #1 above was mounted to the back of the CMOS chip using the copper clips and also using the needed spacers. Thermal paste would be used.
In addition to Method #2 above, try to insulate the tripod connector and connect it directly to the CMOS assembly frame. It is screwed into the frame at the bottom of the camera with 2 small screws. These screws are in a position that makes it difficult to loosen them, without disassembly of the camera beyond the steps taken in Part 1. An option is to fashion a small right angle screwdriver from a jewelers screwdriver by bending its tip. If these screws could be loosened, an insulating material would be placed between the connector and metal camera frame. An "L" shaped aluminum runner could then be used to connect the tripod connector directly to the CMOS assembly frame using the existing CMOS assembly hold-down screw:
Before attempting a peltier cooling method, I need to test the recently modified (filter removal) camera for astrophotography. Nighttime temperatures here in Northeastern PA are usually below 50 degrees most of the year so the need for doing a peltier mod is not as great as if in warmer climates.
Dark Skies,
Gary
I recently heard from Mike Kudenov who added peltier cooling to a 300D in a different way:
http://glogg.jupiter-io.net/300D/
UPDATE: In April 2008, I completed the modification of a Canon 450D (XSi) to remove its IR cut filter. I built a whole camera cooler for the camera using a peltier device from a beverage cooler. Modification and Peltier Cooler Construction plans can be seen HERE.
telescope eyepiece astronomy astrophotography televue eyepieces telescopes astronomy eyepiece dobsonian telescope digital camera