Looking good Glen. One suggestion, only. Check that the usb/remote board will fit back in place, cleanly, before fixing and sealing the copper finger. If not, sharpen that second bend. You can use metal form work a hammer/mallet to punch it into shape - aside from a vice.
Yes Rowland I have already checked that the little PCB with the connectors will fit back in place. I had considered just leaving it out, well taking it outside the camera and mounting it on the bottom as the ribbon cable was long enough - that way the bend would not have to be done, you could take the finger straight out the side with maybe a little spacer placed there to fasten the finger onto. I seem to recall that someone did remove it to the outside in one implementation of the cold finger. One advantage that presents it that it would be possible to carry more copper area or make a couple of pipes to allow more efficency in the cooling of the finger. That's an experiment for another time.
Depending on how you intend cooling, more or less copper is beneficial. I think the reason that mod moved the small pcb outside the camera was that attention to detail was less important. As you can see there is no need to leave it out with a little extra work. At the end of the day, the thermal resistance of your active heatsink/TEC/copper finger/sensor coupling will decide the efficiency of the system.
I am working on a couple of design changes for my cold finger system, which is why it's not finished yet. There are a couple of condensation management approaches I want to trial.
The other change is in the TEC/Heatsink/Fan mounting.
Plenty of work to do.
It took me quite a while to sort out the condensation thing. Last weekend at the SVCamp the dew was heavy both nights - as mentioned elsewhere, the setup ran dew free all night.
I took special care to expose the back of the clamp plate and seal the drainage area. A layer of ice about 2 - 3mm thick accumulated over time and stayed there until I switched the cooling off, some 8 hours later.
I always tilt the camera so that any melt water drains clear of the camera anyway - and even when I neglect to to this, I've never had a problem.
The only time I ran into serious condensation was when, for some insane reason, I decided to enclose the back of the clamp plate. Nothing like experience in the field, even if it did mean a strip down to dry out the camera - no problems since.
Rowland that sounds like you were using a cooler box and not the cold finger? Do you have the finger working yet?
I have found a fairly easy way to insulate the finger inside the camera - Plastidip paint (its a rubber spray formulation that insulates - available from any Supercheap Auto store I think). Just tape over the contact patch areas for the TEC and the sensor and spray it (takes about 4 coats for a good skin).
Rowland how are you coming along with the control circuits? I am going to fix my temp sensor onto the side of the sensor mounting plate. I would like to include a humidity sensor, how does yours work?
Hoping to powerup the finger tomorrow. Photos will follow.
Glen. I have had the cold finger working on my 1000D for several years and have never built a cooler box.
I am yet to complete the modification of the 450D pending completion of the v3 electronics package - in a nutshell I have been perfecting the art of cold finger DSLR cooling for some time.
As mentioned, I have found a way to run condensation free, even with heavy dew.
The electronics package is a major improvement on the previous version but I am not using a humidity sensor.
Note: A previous version of the electronics did use a humidity sensor. I still have the code for the humidity sensor, but choose not to implement it because it's not really much use in my part of the world.
I recommend running a dew strap on the scope and I always run the sensor defogger - except v3 of the electronics package lets you turn the dew strap and sensor defogger at will. But!!! it will not let you turn them off in conditions of low air temperature/potential dew formation. Auto protection!
If you are imaging in warm humid conditions heating can be turned on explicitly.
I am yet to complete the operating manual for the electronics. The board is populated except for two items - awaiting delivery.
I am happy to send a board your way - how are your programming skills?
Finished my cold finger 450D today, and I have attached some photos. I didn't have time to do a real good job with the attachment and insulation of the TEC, so excuse the duct tape holding the insulation together. I rushed to get it insulated so I could run a test tonight. If you have a close look at the finger attachment to the sensor frame you will see I chose to make the nylon screws into rivets by melting the rear of the screws with a soldering iron - there is not much room below the sensor frame and I believe by turning them into rivets I have made it as strong as I can. You can also see the additional copper strips that I added to bridge the cutouts and hopefully transfer better; and the Plastidip rubber paint that I used to isolate the finger.
So here is the Test Results:
First I ran the system to cool down the camera to see how far below ambient I could get it. Remember when I built a cooler box with this same TEC it got down to Delta T of 16.9C. With the cold finger running (and the camera turn off) the internal temperature dropped much quicker than the cooler box and within 20 minutes it was down to 8.9C. Ambient was 26C, so the drop (delta) was 17.1C - pretty good for a taped up job.
Turned the camera on (running on the camera battery which does heat up a little over time). Started a run with my interval metre for ten Dark subs at ISO800 of 5 min 20secs (320 secs each) with a 20 sec delay between subs (to see if cool down period was effetive).
With the camera sitting at 9.0C the run worked out like this:
Sub 1: Finish Temp 9.3C
Sub 2: Finish temp 9.6C
Sub 3: Finish temp 9.9C
Sub 4: Finish temp 10.1C
Sub 5: Finish temp 10.3C
Sub 6: Finish temp 10.2C
Sub 7: Finish temp 10.2C
Sub 8: Finish temp 10.2C
Sub 9: Finish temp 10.2C
Sub 10: Finish temp 10.2C
So in 3200 seconds (53.3 minutes) of darks the temperature rose only 1.2C and I suspect some of that is can be attributed to battery heat within the camera, and the Liveview screen being on. After five subs the temperature stabilised and stayed the same for the rest of the run, this is the active base I believe.
There was no evidence of the external body of the camera cooling significantly and no condensation on the camera body, in the lense, or on the area where the finger enters the camera. Internally, it was purged with argon before I started so no condensation.
When I stopped the test, leaving the camera powered up, the temperature dropped back to 9.3C within 7 minutes and stayed there - so I think that's the 'on power' baseline with no activity (and a warm battery).
Once I turned the camera off the temp dropped back to 9C within 4 minutes, at which point I turned the system off.
So I am pretty pleased with the results, I still have to have a good look at each of the darks but I think they will be ok. One thing I need to address is the fan mount, as it is transferring vibration to the camera, which will be a problem during imaging. There is no isolation of the fan - its screwed right into the vanes of the heat sink - so I will be looking for a better heatsink fan solution (anyone recommend one?).
Photos are attached, the last two show the beginning of the test and the temp after three subs.
*** Update: Once the camera had sat overnight I removed the back of the camera to verify the effectiveness of the argon purge and there was no moisture present anywhere internally.
I have been working on a cold finger support bracket to carry the weight of the heatsink/fan and take stress off the finger attachment points on the sensor frame. Photos of the prototype are attached. Being carbon fibre it weighs very little, but is strong, supports the finger in the x,y,& z axis, acts as the backing plate for the fan/heatsink attachment point, and can be used to mount the cable connector. As usual a good epoxy is the only way to bond carbon fibre. The finger is insulated with Plastidip rubber paint everywhere except the contact patch area. A gas bag can still be used to enclose the camera and I will have another photo of that shortly.
A very neat solution Glen. Until recently the electronics box on the bottom of the camera served the same function, but with the battery grip holder a different solution is required. Looks good.
Completed the Phase Two prototype today and ran a test. Phase Two involves the new carbon fibre bracket, the replacement of the heatsink/fan that came with the TEC, with a CPU Heat Pipe Cooler (Deepcool Gammaxx 200). This cooler has a slightly smaller fan (92mm vs 100mm) but with sintered copper pipes it is going more efficient; it also weighs about the same as the original. I picked the sintered copper pipe cooler as it performs much better at all angles than wick or grooved heat pipes. I found a good article online that compares the performance of different heat pipe types and the effects of orientation (relation to gravity) on performance, it is worth a read if your interested, as telescopes slew and rotate so orientation is changing. Link is here:
So from a room ambient of 22.1C the sensor temperature quickly dropped to 0C and kept going right to -3C, which is a delta T of 25C - which is a good improvement over my Phase One system that achieved a delta T of 17C.
On a nice cool night this system should be able to get down below -10C easily. Considering that I had no insulation on the cold finger outside the camera other than the Plastidip Rubber spray, I am pretty pleased with that performance, the finger iced up pretty good. Have to put it down to the much better heatsink/fan combo. It also has no vibration transfer from the fan to the camera. There was no moisture apparent in the bag, which I had filled with argon, so no fogging, no condensation inside, etc. it looks terrible but it works ok and all camera functions and controls work fine. I used my AC adaptor for camera power so battery change will not be an issue, but consider that if your thinking of bagging the camera; you don't want to be opening it up to change the battery unless your prepared to refill the argon.
Photos are attached.
I am tempted to buy one of the high performance single stage TECs from the US to see how far I can push single stage cooling while still staying within the limits of my controller power.
Well done Greg. Great result. 25C is pretty much what to expect and adequate for most work. I'm going to try the Argon thing once all is finished with the latest control system.
Unfortunately, cooling is about diminishing returns, and the more efficient the hardware the better the experience.
Managed to get in a good test run last night, two hours of constant running on the 10" Newt with all the support systems attached, imaging nebula areas around the southern sky. I had the controller set to -5C initially, going down to -10C for the last hour. No issues with the controller operation, other than the little fan on the box making too much noise and it changes tone each time the relay switches in the PWM - which is one way of telling its all working as it should. I noticed that the set point over-shoots slightly (thermal momentum I guess), and on the warm up to the d value (which I had set for 2C) the PWM would start as programmed but it would take some time for the sensor temperature to repond and the temp would climb up another degree until the cooling caught up.
I had the argon bag on the camera for the entire session, and other than condensation on the outside of the bag, there was nothing happening internally.
At the end of the session, checking through the images, I noticed some spots on one side on the images of bright nebula clouds, zooming in on them I thought there was frost on the sensor or front filter, and immeadiately assumed that somehow I had some condensation happening, so I shut it down at that point.
Today, I took the adaptor off and opened the shutter to see if it was still there, and yes i could see it. I tried cleaning it down through shutter with a brush and cleaning fluid but sure enough it was on the inside, so I tore the camera down again, to get to the sensor assembly. It turns out it wasn't condensation - some dirt/smudge on the internal side of the anti-alising filter on one side. It only showed up on bright object shots. How that got there I have no idea as I know I cleaned it during the mod and assembly. Anyway its clean now and I cleaned the sensor again as well. It's all re-assembled now ready for another go when the cloud clears.
Here are two links to the sample subs (normal full spectrum and colour corrected) - see if you can find the spots.
Managed to get four hours of imaging last night with the Canon running at -7C the whole time (ambient at start was +18C). The humidity was 80% and there was alot of dew. The camera was argon filled, and bagged in argon. No condensation other than on the external surface of the bag which is easily wiped away. The temperature controller performed well with the control value set to 1C there was less over-shoot and undershoot of the target. I'll consider this mod for my camera to be successfully completed and operational. Good luck to the others about to undertake this mod. Thanks to Rowland for this thread and his assistance.
That's a very good result Glen. The images of Eta look very smooth.
I'm sold on the Argon. The heat sink sides seems like a good place to terminate the bag and seal off with tape. The only place I see potential for leakage is past the Astronomik clip-in filter - perhaps the seal is adequate providing the camera is not face down. This thread could go on forever.
Rowland I run a MPCC coma corrector (Baader) on the front of the camera, this creates a sealed chamber behind it and no argon can leak out. Even if a coma corrector or similiar is not used you can still screw on a clear glass filter on the end of the t-adaptor tube to create a seal at the front.
As I have little time and very little technical expertise, over the next month I will be getting my Canon 400D cooled using a cold finger mod by Luis Campos is Europe. The camera is already spectrum modified.
One of the things I am wondering about is the Signal/Noise ratio that you are finding with your cooled camera?
Previously, around 200 seconds at ISO1600 for my 400D seemed to be a good compromise. However, I wonder what the sweet spot will be once I drop the ambient by 20 or more degrees?
John, that is actually a pretty big topic on its own and worthy of a separate thread. I can't be sure what the actual S/N ratio is at this point. What can say is that individual subs shot at ISO 800 are showing no noise grain that I can detect, even when I enlarge the sub. Sure I still have the odd hot pixel that was always there.
Craig Stark has done alot of research on the signal noise in Canon DSLRs and comparative performance with CCDs. Here are links to two of his papers that are great reading on this subject:
The first deals with profiling long exposure performance.
Unfortunately my New Moon dark site trip was rained out this month. I had intended shooting a range of target objects at different ISO levels and with and without cooling running. Now that is put back.
In my few test shots to date, I decided not bothering with darks but have limited shots to share because of this weather holding me back. I have a couple in my public gallery on Astrobin but they have to be converted to jpeg to go on there.
Now as to what I used to do. I always shot at ISO 800 simply because I had past research that indicated that it minimised noise (obviously compared to 1600), and was the sweet spot for an uncooled camera. My subs lengths, generally ran from around 200" to 320", depending on the brightness of the target, whether I was on my pier or the tripod, etc.
I still have the 300" darks from my first test run with the cooled camera, and can have another look at them but am not really equipped to do any comparative analysis other than using my eyes.
Just modified a spare sensor assembly for the 1000D. Images showing a method of removing the ircut filter in one piece with no need to remove the plastic frame and break the seal.
Do this after fitting and sealing the cold finger to the sensor.
Eventually, I will fit clear glass in place of the coated lowpass filter - experimental at the moment.
The low pass filter is removed along with the rubber seal which is adhered to the bottom of the glass. Double sided gel tape 21 x 19mm is stuck to the face of ircut filter with a piece of PCB on top. The glue is cut in the corner recesses and the ircut is levered away - no mess, no contamination.
Before lifting the ircut out of its seating and exposing the sensor face, paint a very thin layer of silicon sealer (neutral cure - selleys roof and gutter) in the low pass filter seal channel, then lift the ircut out taking the backing seal with it - else, just leave it in place, if it doesn't come out.
No time for photos of this bit of the operation - replace the lowpass or clear glass straight away. If replacing the ircut with an astro filter change as quickly as you can, sealing the corners afterward. Then replace the lowpass. I'm using a clipin astro filter so no replacement of the ircut.
Quickly replace the lowpass filter with its seal and leave to cure. Not sure if it helps but I put the whole assembly in a clip lock bag with a dessicant and leave overnight.
The result; -10C and no condensation in the sealed cavity.
Next step is sealing the camera and filling with Argon. Meantime an SMD resistor network is heating the lowpass filter glass ~20ohm 5v. All works very well. Ramping the heater output along with cooling level.
Added images. SMD front glass heater and the ircut previously removed. The heater is a standby. It works remarkably well with little to no effect on the maximum differential.
Now to the Argon bag. I had a good look at sealing the camera internally and decided it was doable but probably less reliable than a snug fitting bag, as per Glen's setup.
