The heater looks ugly but works a treat. Rather than the brute force treatment as before, I'm getting -10C and all clear of condensation on the glass. The maximum differential is not taking a big hit with the heater just warming the glass above dew point.
Given that I want this set up to be portable, and I have no wish to use a computer, and looking for ways to reduce the size of the power supply, Argon is not going to be all that convenient for me. Definitely the best way to go otherwise, but right now it's just a headache. I'll come back to it given time to think it all through.
Given that I want this set up to be portable, and I have no wish to use a computer, and looking for ways to reduce the size of the power supply, Argon is not going to be all that convenient for me. Definitely the best way to go otherwise, but right now it's just a headache. I'll come back to it given time to think it all through.
Rowland, I agree that the argon filling can be problematic, and the bag is a pain to install and seal while providing exit points for the intervalmeter, battery eliminator cable, or USB connector. I have used it with just the intervalmeter and the battery eliminator exiting the bag at the same point but have to assume it leaked somewhat despite being taped up. I have bought a water proof camera bag from ebay but it is junk and no better than a standard ziplock bag with an adaptor cutout. Dedicated underwater boxes for the Canon are a good solution but they add too much weight to the focuser, and cannot seem to be adapted for focuser attachment. So I will continue to work with the bag. I have a dark site trip coming up so a good field test is looming.
Glen. I had a bicycle pump hooked up for a pressure leak test, after carefully and neatly sealing the bag, only to find leak after leak. Eventually, even the silicon around the wires gave way. Wrong materials, I think.
I'be tried taping it up, but it will be a nightmare to undo and redo for repairs or modifications.
Glen. I had a bicycle pump hooked up for a pressure leak test, after carefully and neatly sealing the bag, only to find leak after leak. Eventually, even the silicon around the wires gave way. Wrong materials, I think.
I'be tried taping it up, but it will be a nightmare to undo and redo for repairs or modifications.
Rowland, I agree it is a task to undo and redo, I typically just put a new bag on if I had had to remove it for any reason. Re your pressure test, I don't agree that's a good way to test, as it will normally sit at atmo pressure and not be subject to pressure stress - it's there as a simple barrier to keep the gas contained (not a pressure vessel). Heck even a normal drinking glass will contain argon as it is to heavy to move upward against gravity - unless there is a breeze to disturb the surface and blow it out. My long imaging run test did not produce any condensation or fogging inside the bag (or the adaptor tube) and the images were great, which tells me the argon is doing its job. But yes it can be a pain to setup.
You're right Glen - a bit extreme. With the battery grip on it was necessary to load it up to see whether the seal I made was leaking - there seemed no other way of doing it. I think Argon is the answer in the long term.
Much of what I have implemented on this mod is the advice given in the past by the kind people on this forum, which out of curiosity I chose not to follow. Right now, the camera is sitting on -10C +/- 0.3 with not a sign of condensation on the sensor glass (low pass filter). Air temp is 15C. A working 25C delta is just fine and it's wet down here after the rain.
Just update on the Argon bag use. Last week I spent four nights imaging up at the dark site at Bretti NSW, and the camera stayed in the same bag the whole time. You may remember that I flushed it with Argon when I put it into the bag (via the port I made on the side). The only change from the test setup was that I slit the bag slightly in one spot and refreshed the Argon in the bag before the first night.
The nights dropped from 6C to about 2C by midnight, and there was heavy dew there that shut down some of the others that did not have adequate dew protection. The external surface of the bag did get dew on it but there was nothing internally. Simply wiping the external surface of the bag kept the Liveview screen usable. I had the cold finger controller set for -10C and it stayed there for four or more hours at a stretch each night. That temp required minimal power consumption and I noticed that it held -10C for quite some time before kicking back on (no doubt due to the cold soak at that point and the low ambient).
I kept a dew heater strap wrapped around the focuser barrel to prevent the front screw in Baader UV/IR Cut filter from fogging up on the outside (inside the adaptor barrel was filled with Argon, between the filter and the Baader coma corrector, as was the space behind the adaptor).
My images subs came out great, with no evidence of frost, condensation, etc.
Re power consumption, in the dark site field you will need a good size 12V battery to drive the cold finger (TEC, temp controller/fan assembly, etc). I worked out that about 82AH would be needed for a typical night assuming 6AH requried by the TEC). I took a 100AH battery just to drive the camera cooler gear and it was overkill but better to have too much. I found that by holding the sensor at -10C there was minimal power usage at that ambient temp, and the sensor would sit at -10C for most of a five minute sub before turning on again.
After the second night run I again refreshed the Argon in the bag as a contingency, but there had been no sign that it was necessary. Over the four nights, the camera cooling system performed very well, and I had a fair amount of image data - unlike my mate who was trying to get his expensive QSI camera to work.
If you'd like to see a couple of the images, they are here: (first is Eta Carine, second is M83 - which is cropped and stretched so has some evidence of noise which I did not clean up)
Looks good Glen! If you haven't already, it might be worth experimenting to see at what point your darks become clean so you can save on the power requirements. My 1100D for example seems to be pretty much clean besides a few hot pixels when ambient is below 5C. Yours may be similar, but may not require sensor cooling to -10 to achieve the desired effect. Just a thought.
This thread started with the fabrication of a cold finger to fit a 450D. Glen has provided a lot of info about how he modified his camera. So rather than starting again I am picking up where I left off, finally making time to put experimentation into practice.
The first task was a spectrum conversion. Removal of all the factory filters and fitting a modified full frame astro filter in place of the AA filter. The filter is siliconed in place to exclude dust and moisture.
Secondly, fitting an improved resistance heater to the face of the astro filter. Double sided kapton cut to the AA filter dimensions on which 3.3ohm resistors and connecting wires are
held in place for soldering. 4mm strips of double sided kapton are stuck to the edges of the filter on which to fix the heater. Strips of kapton over the heater hold it in place. each resistor outputs about 200ma at 5v.
All the circuit boards are sprayed with lacquer to protect from moisture.
Given that the battery housing with all the control electronics will be moved to this camera, there is little to be done except fitting a temp sensor to the cold finger.
The 1000D may be available to anyone serious sbout cooling.
Hmm, back into eh Rowland ?
What is the thermal transmisson method between the sensor rear and the heat sink, just proximity or some mechanical means, heat paste, silicon etc ?
(Must go back and read some of the earlier postings on this thread, catch up time)
EDIT: After a quick review, I don't think my copper slab idea in the other thread will work for the 450D or it's proteges. The KM 7D has the sensor uncovered at the rear and a bit of space to play with, the copper inserts into the back plate and adds maybe 1 mm extra backwards. Unless I made some serious mechanical mods to the Canon it doesn't look too feasible.
Experiments will continue nonetheless.
Back into it.... for better or for worse, Brent.
The copper is hard against the back of the sensor with a smearing of heat paste. The back of the copper has a layer of duct tape to tightly fill the gap between the copper and PCB.
The sensor pins are soldered to the circuit board on the 1000D, 450D and 500D, which makes for easy conversion. And the bavk of the sensor is flat and bonded to the sensor which makes for even cooling, unlike the sensor mounting frames in later Canons. Very convenient for 1.2mm copper sheet.
One big advantage of the tight fit of the copper plate behind the 450D sensor is strain relief and stiffening of the whole TEC/heat sink/fan mount which has much less chance of putting torque on the sensor assembly, the downside is the possible direct transmission of fan vibration to the sensor assembly. The fix for that is to isolate the fan on silicon pads (which come with some quality fans), choose mag lev fans where possible, and use nylon screws and spacers when attaching the finger to the sensor assembly frame.
Here's an old 1000D sensor with frame and PCB (including metal shield) Identical in construction to the 450D, except fpr the megapixels, of course.
The gap is 1.3mm. The tongue of the cold finger is nominally 43 x 27mm to cover the sensor back completely while not touching the sensor pins. The sensor pins must be insulated from the edge of the copper. I use thin plastic strips 45 x 2mm inserted either side of the cold finger. They slide into place alongside the row of pins.
Had a chat to a work colleague today. He's the 3D printer expert tech. He's been experimenting with a 2 pot silicon rubber compound for which he makes the molds on the printer of course. (You ought to see his squid jig bodies in blue silicon ).
Anyway he is going to make me a thin, 1.5 mm flat sheet of silicon rubber. I can press that up against the back of the sensor with the copper finger. It's temp tolerant from 200C to -53c and it should make a better physical contact for the finger. Also keep the back dry, no air means no moisture although I'm looking into the argon bag solution as well.
In the meantime I've milled most of the copper island away to reduce weight and provide another TEC surface point.
Rowland all of that exposed copper is going to frost up as you know, do you have an insulation plan within the camera or going to leave a sacrifical frost patch outside the body? I sprayed mine with Plastidip rubber (4 coats) and it has held up well.
