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Canon T3i (600D) filter and cold finger mod.

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#26 Midnight Dan

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Posted 15 August 2014 - 08:04 PM

At this point, I need to wait for the controller and project box to arrive so I can wire things up.   BUT … since everything was in place and the camera was operational, I was able to do some testing.

 

First simple test was to determine what delta-T I could achieve with this setup.  I used the temperature sensor I had glued into place as the cold reference point, and I used a digital thermometer to measure the temperature of the heat sink on the hot side.  After letting it run for 15 minutes or so, things seem to have stabilized.  

 

With an initial ambient temperature of 27.5°C, I could get the sensor frame temperature to 11.2°C, with the hot side at the heat sink going up to 40.2°C.  So my delta T was about 29°C from hot to cold, or 16.3°C below ambient.  Now keep in mind that this was with no heat load from the sensor because it was not in use.

 

I went ahead and ran some tests over time with the sensor in use.  Here's the data:

 

CoolerGraph_zps8d583e6d.jpg

 

The idea of the test was to see if the cooler would fare any better when starting with a warm sensor or a cooled sensor.  The first phase allows the sensor to heat up without cooling.  The second phase is with the cooler running.  The third phase uses 1 second exposures every 60 seconds.  This is essentially with no (or minimal) heat from the sensor, but allowed me to read the exif data every 60 seconds to see what the sensor temp was doing.  The last phase is with the normal 60 second exposures and cooler running.  Both the 2nd phase and 4th pause ended up at about 20°C on the sensor temp reading, which is about 10°C cooler than the sensor temp without cooling.  Not as good as commercial CCD camera cooling, but should be adequate for what I want to do, which is keep it from heating up into the "noisy zone".  

 

When the cooler is running, I can see that the limiting factor is the heat sink.  It needs longer fins, and more of them.  The heat sink gets quite hot to the touch, and the air moving through it does not pick up a ton of heat.  As I feel the air coming out of it, it seems only very slightly warmer than ambient.  I might try another heat sink at some point, but for now this seems to work reasonably well.

 

Next test is to take some darks and see what effect the cooling has.

 

-Dan



#27 Mitchell Duke

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Posted 16 August 2014 - 02:39 AM

I used a copper heatsink and a high speed fan on my cooler to remove as much heat as possible. Mine is a little different than your version. I cut out a square where the LCD closes and installed the peltier directly on the sensor housing. However mine will be used for astroimaging only.

#28 Midnight Dan

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Posted 16 August 2014 - 09:57 AM

Hi Mitchell:

 

Yeah, copper would work a lot better since it has double the thermal conductivity of aluminum.  

 

What kind of fan did you get?  I purchased a moderate speed one because I was concerned about noise and vibration.  Do you have any issues with vibration?  Do you know what kind of bearings yours uses?

 

-Dan



#29 Midnight Dan

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Posted 16 August 2014 - 10:11 AM

Here's the dark test.  I sealed up the camera from light, and ran four 10-minute darks in succession at 3200 ISO for a worst case scenario.  In the resulting images, I cropped out a 200 x 200 pixel section from the center to show here.

 

I had run this test previously with the unmodded camera.  In fact, I had 2 T3i's and was trying to determine which to use for astrophotography.  I had purchased a body-only for this mod, but then decided I'd test my older "family" camera to see which performed better.  The old one was noticeably better so I used it for the mod, and am using the newer one for our family photos.

 

FullSizeNoisecompare_zps0b1a26f6.jpg

 

At the time, I had BYEOS set to Farenheit, so the exif readings are in °F.  In these images, you can see quite a bit of noise, but you can also see how it increases over time as the sensor temp increases.

 

This next set of images is the same test but with the cold finger running.  I'm using Celsius now, but I put in the Farenheit conversions for reference with the previous images:

 

ColdFingerDarks_zps75889fc4.jpg

 

This is what I was looking for!  Not perfectly clean, but a WHOLE lot better than before, and it maintains a reasonable temperature over time.  Even the 70°F image looks better than the previous one at the same temperature. I'm guessing that the temperature for the exif data is being measured somewhere close to the camera sensor, but not right at the pixels.  If so, the exif temp could read the same, but the two images probably represent a few degrees difference in actual pixel temperature.  Just guessing though.

 

Anyway, I'm happy with this!  There's more I could do to make the cooling more efficient, but I'm not sure it's worth much more effort at this point.  I want to get the camera back in action at the scope!  I've been unable to image for a couple of months now while I've been working on this.  Probably should have done it as a winter project. :p

 

When I get the controller and project box, I'll post more pictures.

 

-Dan


Edited by Midnight Dan, 16 August 2014 - 11:02 AM.

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#30 Mitchell Duke

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Posted 16 August 2014 - 03:44 PM

Believe it or not I used a 80mm ball bearing fan. It was an old cpu fan. I ended up using it because the one I ordered was defective and I could not wait to try it. Vibration is no issue at all, and the copper heat sink stays cool. With no delay between 7 minute subs I get 25 degrees below ambient. My only problem is the sensor fogs over everytime. My idea was to try pumping warm air over the sensor, because nothing has worked so far :(

#31 Midnight Dan

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Posted 16 August 2014 - 09:29 PM

 My only problem is the sensor fogs over everytime.

 

That's one reason I'm putting in a controller.  When the ambient temperatures get lower, I don't want to cool the sensor too much.  I'm shooting for "good enough".  The 70° sensor temps shown above seem to me to provide a "good enough" level of noise.  I just wanted to avoid those really noisy images when the sensor heats up.  I also want to be able to keep a more consistent temperature over the course of multiple long exposures, which this seems to do.  That will make it a lot easier to match darks.

 

But if I keep the sensor at reasonable temps, rather than trying to go for the coldest I can possibly get it, then I should have less worries with condensation.

 

-Dan



#32 Mitchell Duke

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Posted 17 August 2014 - 12:06 AM

In Georgia I think the dew point is the same as ambient LoL

#33 Midnight Dan

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Posted 17 August 2014 - 06:41 AM

In Georgia I think the dew point is the same as ambient LoL

 

I think that's called rain. :lol:



#34 ScottP

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Posted 17 August 2014 - 12:13 PM

well, down here in the "deep south" it's called atmosphere! But honestly I don't think it's that much better where you are Dan. While the temp MAY not get as high I'm pretty sure the Gulf Stream does it's best to provide you with plenty of humidity... but maybe not. I've only been to your part of the world a couple times and one was winter.

 

Dan, I have to say that this mod of yours is VERY impressive. The attention to detail you exhibited during the process was  definitely above average, I dare say exceptional. :bow:

You can bet I will be following this template VERY closely when I finally get around to doing mine. Living in Mississippi we have such high temperatures even in the evenings that I have absolutely NO doubt it will help me once I can finally pull all my projects together and start imaging.

 

I have a couple of questions though...

 

1. you said " I slid some pieces of shrink wrap over the screws to provide a little thermal break between the screws and the heat sink"

     Could you help me out on this as I really don't follow what you're trying to say. Maybe I'm being dense on this one but I just don't follow.

 

2. all the white "insulation strips" that you put around the TEC plate... is this some piece of "stuff" you just had lying around and used or is this a specific material and if so what is it?

 

3. you said "I also purchased a silicone vibration pad to help isolate any fan vibrations from the rest of the system"

    Do tell... inquiring minds... well at least MIND ... want to know. I would DEARLY love for you to share what this is and where you got it...

 

4. One more question.... how did you decide where to put the temp sensor? Was it purely dictated by physical size limitations or did you decide you felt as though that was the best location?



#35 Mitchell Duke

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Posted 17 August 2014 - 05:21 PM

You can also use plexiglass to block heat from the pelt to increase cooling.

#36 Mitchell Duke

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Posted 17 August 2014 - 05:22 PM

Im going to build an internal dew heater for the sensor to keep the chip cold.

#37 Midnight Dan

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Posted 17 August 2014 - 07:25 PM

I have a couple of questions though...

 

1. you said " I slid some pieces of shrink wrap over the screws to provide a little thermal break between the screws and the heat sink"

     Could you help me out on this as I really don't follow what you're trying to say. Maybe I'm being dense on this one but I just don't follow.

 

2. all the white "insulation strips" that you put around the TEC plate... is this some piece of "stuff" you just had lying around and used or is this a specific material and if so what is it?

 

3. you said "I also purchased a silicone vibration pad to help isolate any fan vibrations from the rest of the system"

    Do tell... inquiring minds... well at least MIND ... want to know. I would DEARLY love for you to share what this is and where you got it...

 

4. One more question.... how did you decide where to put the temp sensor? Was it purely dictated by physical size limitations or did you decide you felt as though that was the best location?

 

Hi Scott:

 

1. The heads of the long screws were countersunk into the base plate, which is on the cold side of the TEC.  Those screws then went through holes in the heat sink, and then through the fan to hold the whole mess together.  If the screws were touching the heat sink, which gets quite hot, they would allow heat to flow from the heat sink through the screws and into the cold base plate, which would warm it up.  So I drilled the holes in the heat sink larger than they needed to be, and slid a piece of shrink tubing over the screws to keep them from directly touching the heat sink.  While not a great insulator, the shrink tubing at least breaks the metal-on-metal thermal path of the heat from the heat sink into the screws.

 

2. The insulation strips were cut from a roll of adhesive backed weatherstripping I got at Home Depot.  They sell a variety of size and the one I got was 3/16" thick and 3/4" wide on the roll.

 

3. I got the fan, the vibration isolation pad, the rubber washers, the Arctic Silver thermal grease, and the Arctic Silver thermal epoxy from frozencpu.com.  They sell the vibration pads in various sizes to fit most if not all of their fans.

 

http://www.frozencpu...ml?tl=g36c15s57

http://www.frozencpu...n_Silencer.html

http://www.frozencpu...er_Grommet.html

http://www.frozencpu...l?tl=g8c127s447

http://www.frozencpu...l?tl=g8c125s446

 

4. I wanted to put the temperature sensor as close to the camera sensor as I could.  I couldn't really get it on the sensor itself, so the sensor frame seemed like the closest place where it would fit.  

 

-Dan



#38 ScottP

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Posted 17 August 2014 - 09:40 PM

Like I said, attention to detail!

 

I will honestly admit that the thermal transfer from the screws back to the cool side probably would not have occurred to me. Kudos!!! And the test results were what I was hoping for. With a decent temp controller all you will need to do is check each night for the dew point and set the temp a few degrees above that and you should be golden. Heck, like you results showed also as long as it's about 70degs the camera seems very quiet.

 

Really a top notch job. I can't wait to see the final product with the project box and all.



#39 Midnight Dan

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Posted 31 August 2014 - 10:58 AM

I received the controller board and finished up the mod in the last few days - just in time for the bad weather to set in! :p  But … since it's raining, time to post the final photos.  

 

This one shows the wiring inside the project box and rear of the controller.  The controller is essentially just a thermostat.  It comes with a temperature probe that I previously glued onto the sensor frame, and you can see the other end plugged into a small white socket on the rear of the board.  On the right is a green terminal block that allows you to apply 12VDC or AC.  Since AC is allowed, there is no particular polarity required and therefore the 12VDC can be wired up in either polarity.  On the left is another green terminal block which is connected to the relay that turns power to the TEC plate off and on at the proper temperature.  I wired up the fan to run all the time.  The toggle switch at right connects 12VDC to everything.

 

31ControllerWiring_zpsbb426336.jpg

 

Here's an image of the controller board installed in the project box.  Note the 3 buttons under the display which are used to make settings for the controller board.  In addition to setting the temperature set point, you can also set it for cooling or heating mode, a hysteresis value, an offset for the temperature to calibrate the probe, a delay time, and a temperature alarm - yes it even has a beeper on the board.  Pretty amazing what you can get on eBay for under 10 bucks!

 

32Controllerboardinstalled_zps064270e3.j

 

This photo just shows how I mounted the project box to the cooler.  The main connection is two nylon screws and spacers I got from home depot and cut to length, which connect the box to the heat sink.  Since the heat sink gets quite warm I decided to use nylon screws so they wouldn't carry heat into the project box.  I didn't know if the circuitry would be temperature sensitive or not.  Probably didn't really need to do this, but just in case.  For the 3rd connection point, I used a small brass corner bracket I had laying around,  I trimmed the length of each leg on it with a band saw so that only the first screw hole was left.

 

35Controllermounting_zpse97b2d7e.jpg

 

-Dan



#40 Midnight Dan

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Posted 31 August 2014 - 11:04 AM

And finally, a couple of shots front and rear of the completed project:

 

34Completefront_zps818e9cbc.jpg

 

33CompleteRear_zps558add4f.jpg

 

This one shows how I made an effort to be sure that the camera's battery door and articulating rear scree still work normally.  Another nice feature of using the bottom of the camera for the cooler instead of the side is that all the side connectors, like the usb port, are still available as well.

 

36Doorsopen_zpsf0d5ebc4.jpg

 

-Dan



#41 Midnight Dan

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Posted 31 August 2014 - 11:13 AM

To wrap up, some Tips, Observations, and Lessons Learned.

 

1) Patience is a virtue.
This project took me a couple of months.  Since I couldn't find any online info for the cold finger mod for my particular camera model, it was a learn-as-you-go process.  This meant I spent a lot of time thinking, planning, and trying things.  Since I often didn't know what parts I'd need for the next step, I couldn't order ahead so I also spent a lot of time on hold waiting for a trip to the store or for online orders to arrive.  If you tackle this, hopefully this thread will help you move more quickly than I did.  But this is still a job that requires a careful, thoughtful approach.  Taking your time and working carefully and methodically will pay dividends.

 

2) Do it in the winter.
Since DSLR noise is worse in the warm summer months, it spurred me to tackle this sooner rather than later.  But because it took a lot longer than expected, I lost a couple of months of good summer imaging nights.  Plus, summer is a busy time and “life” kept competing with this job for available time.  This would have been a much better winter project.

 

3) Have the right tools.

… or know someone who does.  For the filter mod, Gary Honis' web site shows the tools needed for camera disassembly/assembly.  Most of those tools, along with a smattering of normal hand tools, are needed for the cold finger mod as well.  But in addition, some metal working tools/skill is required. 
I purchased a Gyros rotary tool kit (cheaper version of Dremel) for $60 from Home Depot for this job and found it to be an absolute necessity.  I got the kit that includes the flexible shaft, which made handling the tool in tight spaces easier.  The abrasive cutoff wheel got the most use, but I also used some of the grinding wheels that came in the kit.  I used a drill press for most of the drilling, but a portable electric drill should work fine. For the screw holes, you'll need a 4-40 tap and a countersink tool.  For cutting the metal parts, I used a small table-top band saw. You can probably use a hack saw instead, but that would add a lot of time and effort.  If you can get access to a band saw, it's a much better way to go.  One more thing – a decent set of metal calipers like the digital calipers that Harbor Freight sells ($20).  These make it easy to get precise measurements, and the pointed metal tips are very handy for scribing measurements on the metal parts at the right distance from the edge.
For the electrical work, you'll need the standard equipment such as a digital voltmeter, soldering iron, wire strippers, etc.

 

4) Take lots of photos!
Even if you have no intention of posting them online.  This is a complicated job with lots of small steps.  More than once I found myself referring to earlier photos of the camera to be sure I had things assembled correctly.  I've noticed that photos have a much better memory than I do! Even if you never need them, digital photos are free.  Take them as insurance.

 

5) Do tape screws to a piece of paper!
This is recommended on Gary Honis' site, but is so important that it bears repeating. For each removal step, tape the screws removed to a piece of paper and write down the step number.  I found this made the reassembly MUCH easier, especially since it occurred a couple of months after the disassembly.  Like the photos, that piece of paper had a much better memory than I did.

 

6) eBay is your friend
For some of the items you'll need, like the controller, project box, heat sink and TEC plate, even the copper and aluminum plates, you'll find a large variety and cheap prices from eBay stores.  The downside is that some of these sources are direct ship from China so the arrival time can be a couple of weeks.  Keep an eye on shipping costs although many sources ship surprisingly cheaply, or even offer free shipping.

 

7) Use aluminum as much as possible, copper only where needed.
Copper is a much better conductor of heat, but is also much heavier and more expensive than aluminum.  Since the cold finger itself is thin, and the heat must be transferred along its length, copper is really the best choice to cool the sensor efficiently.  But I used aluminum for the thicker base of the cooler assembly due to its lower weight and cost.  And since heat is transferred through this part only across the shortest dimension (the thickness) it would not make much difference in efficiency to use copper.  A copper heat sink would certainly do a better job of cooling the hot side, but there are a much wider variety of aluminum heat sinks readily available and inexpensive, and a coper heat sink would add a lot of weight.

 

That's it!  I hope this was helpful to anyone else considering this mod.  If you have any questions, I'll be happy to try and answer them.

 

-Dan



#42 Mitchell Duke

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Posted 31 August 2014 - 02:42 PM

The only issues I had with anything in these projects were the dang screws? The screws actually take a #000 screw driver. The screws are very weak aluminum, and very easily strip. I had to drill out two screws in mine. The PWM I bought worked great for mine. It easily controlled the temp to the dew point. Awesome work on your unit, it looks very professional.

#43 Midnight Dan

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Posted 31 August 2014 - 03:18 PM

Hi Mitchell:

 

Which screws are you referring to?  The ones that hold the camera body together?  Seemed like mine were made of stainless, not aluminum.  I just used a small phillips head screwdriver from a jewelers set and a small torx driver (T-7 or T-6, can't remember), as recommended on Gary Honis' site.  Some of them took a bit of force to get out, but didn't strip any of them.  The only one I had trouble with was the one that held the sensor to the sensor frame as mentioned in the thread above.

 

-Dan


Edited by Midnight Dan, 31 August 2014 - 03:19 PM.


#44 Mitchell Duke

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Posted 31 August 2014 - 04:24 PM

Mine must have been different? The cam body was aluminum screws, and the interior circuit boards were stainless. It was well worth it though, and I was considering getting another cam just to do another project ;)

#45 Nils_Lars

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Posted 01 September 2014 - 01:30 AM

A great piece of work documenting all this , very cool stuff Dan.








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