Cool modding a 5DMKII

[rcheshire]

I've been investigating methods of cooling a DIY refurbished, Astrodon Inside modded 5DMKII (aside from a centralds mod), which led here and there, with mixed results.

This camera makes a brilliant wide field instrument. I love it.

I read somewhere that Spencers use a passive method of cooling the sensor. Basically, bleeding heat to the camera frame - which gave me an idea. Good or bad, is yet to be determined.

As you can see from the images below, I have made a cold plate/finger to fit to the back of the sensor - it will be insulated from the electronics with a moisture barrier.

This particular mod will use a very low power linear driven TEC device installed under the tongue of the cold plate, consuming no more power than my dew heater.

Heat from the other side of the TEC will be conducted to an external active heat sink by a copper strip. The copper strip will be insulated from the camera chassis, held in place by heavy duty double sided tape.

It won't get that hot. Not like the one used on a previous temperature regulated 1000D cold finger, which had a massive heat sink. All it needs to do is take the edge off the dark current without frosting the thing to bits.

The mod could dispense with the TEC by extending the cold plate tongue and fixing it to the camera chassis or extending it outside to an active heat sink, which I think would work very well.

I'm waiting on a 30mm x 15mm x 3.6mm TEC module that will tuck in nicely.

I will add images over time.

[2stroke]

Sounds like a sweet idea using the frame as a heatsink :) It should coup easily with a low wattage tec. I think to many people go nuts using massive TEC's and trying to dissipate the heat, all thats needed as a small tec to coup with the load thats causing the problem. That dsi pro mod works just perfect a 3watt tec does the job just beautify and using the existing passive setup to cool it. This is it here http://www.iceinspace.com.au/forum/showthread.php?t=101266 in case you missed it rowland, lol ill be going the same route by using a very small TEC if the 1100d mod causes to many issues.

Extremely nicely done, hope to see some results soon and progress come along. I think this would own any cooler box out there and maybe the cheapest and best solution to date to achieve less noise without breaking the bank and going to extream's. As alot of testing has shown sub zero temps really arn't needed in newer sensors and if this takes the edge off enough it could be the best solution ever :) Lol this could become a diy kit if you got the heatsink laser cut or pressed out XD

[rcheshire]

I didn't see the DSI - how did I miss that? Yes... my first mod was over engineered.

A kit is a good idea

Agree. Sub zero is not necessary. Just a consistent low temp that doesn't fog up the sensor. Dark scaling used by some processing programs should cope with +/-5C over a nights imaging.

The black spots associated with mismatched darks can be masked by dithering by 12 - 15 pixels while imaging. Seems like the easiest solution.

[rcheshire]

Update. The work progresses.

Moisture barrier for sensor electronics (BluTak pressed around components). I've used this technique before. It is quick, convenient and effective. The cold plate will hold it in place as well.

Fitted cold plate

TEC module - Mistake with my measurements, here. Too wide and blocking the CF card holder. Narrower TEC required. There's a metal retaining tag folded over the plastic sensor filter frame that sticks out 2mm...

At this stage the TEC could be left out. Extending and widening and bending the tongue to contact the chassis, with plenty of contact area, might be adequate. A slim heatsink might do the trick too (40mm x 13mm x 5mm) Perhaps extend outside the body under the CF card to an active heat sink.

Another method might be to machine the whole cold plate from aluminium block with appropriately shaped cooling fins.

This one is destined for a slightly smaller TEC.

[rcheshire]

A bit more progress. Two more images.

A trimmed 30 x 15 TEC. Removed one line of couples and resoldered the +ve wire and plugged with BluTak for testing - finished with silicon. Another option is to use two 12mm square modules (not so readily available) switching both or one for two levels of linear temperature control. I've used a $2 seconds module.

Main board fits nicely in place. TEC wires are a bit of a juggle.

Copper strip to external active heat sink.

Tested at 1.6 volts ~2amps - heat sink only - no fan. Hot side is warm to touch. Cold side bites when touched. This will improve when I get the power supplies sorted out and have a fan running.

12V SMPS will supply 12volt fan and 5A DC-DC adjustable convertor will run the TEC, at 1.5 - 2 volts and ~2 - 3 amps.

EDIT: The $5 ebay Buck convertor, adjustable voltage, will be calibrated to corresponding temperature differentials with reference to an ambient temperature of 20C (room temperature) and corrections applied for ambient temperature variations, applying ROT a table or graph. Setting temperature 2C above the camera internal dewpoint should be relatively easy - it's SMPS. Grounding the camera chassis is a prerequisite as well as good power supply filtering for reducing EMI effects. I don't think this will be too troublesome.

[rcheshire]

Up to the testing phase.

Note: The BluTak moisture barrier will need 10mm wide strips of speed tape on the left and right side for added protection to the tops of SMD components that come close to the backside of the copper plate. They don't touch and as you can see, I have drilled holes to provide clearance to those that sit higher than the sensor backplate.

Finished the TEC installation and added a temperature sensor - it failed and had to be replaced. The replacement was a neater installation than shown here.

Insulated cold plate with speed tape given the proximity of the main board metal covers.

It needs a suitable heatsink. The one I have is too big. Not sure what impact that will have on performance. I suspect the one I am using at 200 watts exceeds requirements by a mile with no added advantage.

At 1.3 volts the TEC pulls just under 2 amps. A further increase in voltage, as suspected, heats the system. So the sweet spot is ~1.25 - 1.35 volts on my multimeter.

A DC-DC convertor which is yet to arrive will provide a little control over temperature control, but not as much as I had imagined. The system is limited by heating of the conducting strip, but this is preferable to using a large external TEC which may risk condensation internally or damaging cold - it's a trade off.

I suspect better performance can be had with an additional and bigger TEC installed along with the heat sink... perhaps just a waste of energy. Alternatively, and possibly a better solution is a lower powered TEC. More energy does not necessarily equate to more cooling with this technology.

I think the TEC is too big at 5A and 4V for the job - 2 amps would have been adequate. The advantage of the conducting strip is that it keeps the air in the camera warm and may assist with defogging of the sensor:question:

Furthermore, I don't know how reliable the location of the temp sensor is in providing an fair estimate of performance. So I will go with the improvement in dark signal as a guide.

Screenshots before and after cooling with dark noise reduction. Left column is cold plate temperature. Right hand is room temp. I haven't evaluated the actual reduction and will get to that later. As far as appearances go, it looks a lot better.

That's it for now.

EDIT: Nearly forgot to mention that the CF door obviously had to be modified. I'm using tape to hold it in place at the moment and have one or two ideas about how to make the card more accessible - WIP.

[rcheshire]

I couldn't resist trying a second external TEC - 15V 8A at 12 volts, reducing the cold to hot side temperature differential of the internal TEC, which is a measure of performance.

Running the internal TEC at 1.2 volts and the external at 12 volts, reaching 20C differential it was turned off allowing the sensor temperature to drift up to the internal TEC max differential of 8 - 9C. With the external TEC at 10.1 volts (need a different power supply to get a lower voltage) max diff was 15C.

A few more degrees differential would be nice, requiring a fresh look at the dimensions of the copper strip and the rating/performance of the internal TEC.

[gregbradley]

Great work. I made a heatsink for a Nikon D70 years ago. Unfortunately I damaged something in the process and it was a failed project.

That copper looks quite thick. Is it about 2mm thick? You could even use thinner copper like .7mm and cut it with snips. Or 1.2mm. You can get that from Austral Bronze or hobby stores often have small sections of copper sheet.

I presume the vast bulk of heatsinks around are aluminium because of cost or is it also very efficient? I would have thought a copper one would leave aluminium for dead.

Greg.

[rcheshire]

Hi Greg. I used 1mm copper throughout. 1.2 is a tad to big for the confined space. I've refurbished the camera replacing several components and flexs.

I'm looking at a better quality tec which is a little thinner than usual and will use 1.2mm sheet to close the gap. It's a bit of a squeeze.

[rcheshire]

The Buck convertor arrived, with two more on order rated at 6 amps. A cost/time effective way to cater for the various voltage/distribution requirements of my setup. The footprint is very small. Given the steady temp sensor readings these convertors are quiet.

http://www.ebay.com.au/itm/130892021014?ssPageName=STRK:MEWNX: IT&_trksid=p3984.m1497.l2649

http://www.ebay.com.au/itm/300688545129?ssPageName=STRK:MEWNX: IT&_trksid=p3984.m1497.l2649

Rated at 5A, input is quoted as minimum 10V - but works down to 8V. Output 0.9 volts minimum, which permits setting the internal TEC at 1.2v (see previous post). An external TEC can be used to control temperature through a second convertor. If small differentials are required in the colder months both convertors can be wound back as required.

In pursuing a linear method of temperature control, buck convertors seem to be the way to go. Essentially, they provided a means of setting a differential, but not a set temperature. As previously explained temperature variations can be handled within reason by dark scaling and any mismatch artifacts dithered out during acquisition of light frames. Aggressive dithering of light frames is a prerequisite for high SNR DSLR images.

The heatsink, fan ON or OFF, handles heat dissipation well, which tells me it can be smaller, providing it's active. Perhaps a relay to turn off cooling in response to fan failure, for protection.

BTW: Tellurex make a 25 x 12mm module only 3.4mm deep rated at 2.5 amps - ideal for the internal TEC application, but I cant find a reseller. Presently, I'm waiting on Tellurex to suggest an alternative shipping method other than the single $97 dollar option for delivery to Aus. Lets see if they come through? The dimensions of this module offer a few more options in terms of room for better insulation of warm/frigid components from the camera body.

[rcheshire]

Picked up an old stock (Phenom II) Cooler Master for this project. The copper base is 39mm wide which is ideal for a 40x40 TEC. Light enough and small enough not to present a significant balance problem, given its displacement from the optical axis.

Heat sink calculation is probably the most complex part of cooling. Sourcing the right heatsink was a challenge. I think this will do it.

Thermal resistance is probably around 0.3 - 0.5C/Watt, which is OK, - a weight/cost trade-off. It will run about 10C warmer than the Alpha Novatech used on the 1000D cold finger mod.

10C is quoted by Tellurex as an ideal ambient air temperature / heat sink airflow differential. That's fine but needs a 0.16/Watt heatsink for this cooling application. I don't need to cool to that extent. 20C would be great for summer time. Winter requires as little as 6 - 8C differential, because the camera is already cold.

EDIT: While on the subject of heat sinks, it is apparent through testing that the 40mm copper strip is more of a heat repository than heat sink. If using a second external TEC there is more thermal mass to overcome before reducing the hot/cold side differential of the internal TEC, with greater power demands.

A better approach is to reduce the width of the copper conducting strip to that of the internal TEC. With the arrival of the more efficient Tellurex ZMax 25 x 12 TEC (regular post) I will replace the existing copper with a 25mm strip ending in a 40mm square to fit to the heat sink.

[rcheshire]

The test set-up is an internal TEC constant at 1.2v and an external TEC rated at 12v 6A. Heat sink as in previous post

Rounding, I found that the temperature differential, starting at 8 volts increased by 1C/volt. A 3 minute exposure at each voltage increase, decreased the differential by 1C. ( an acceptable mismatch and manageable with dithering).

The first image compares performance without cooling and temperature rise measured at the bottom left corner of the sensor frame over 240 seconds.

A graph showing temp differential vs voltage and 3 minute exposure effect.

Noise comparison from PixInsight Noise analysis script and noise evaluation during debayering.

EDIT: It crossed my mind that a two TEC arrangement (not stacked, which is usual) has advantages over a single brute force external TEC (which can achieve moderately higher temperature differentials) because the metal in the vicinity of electronic and mechanical components is warmed by the hot side of the internal TEC.

In this installation, the hot side of the TEC is immediately adjacent to the face of the sensor and the rim of the chassis which surrounds the sensor face. There is also a small air gap between the chassis and the sensor.

The Astrodon filter is clear of condensation at -3C, measured at the bottom left corner of the sensor frame. Unfortunately Backyard EOS is not recognising the camera, which prevents reading sensor temperature.

An essential component of cold finger installations is a metal collector plate (practically speaking, the bit that clamps the TEC to the heatsink) on which ice and dew forms, keeping the internals free of the same. This was observed by another DIYr, and given 4 different conversion styles to date, it seems to be correct.

[rcheshire]

I was running a few more tests the other night after fitting an improved heat sink clamp and graphed the data yet again. Interesting. The original set up was obviously not clamped adequately as the diferential has increased to 19.5C with 1.21v and 11v to the internal and external TECs respectively.

Furthermore the increase in C/volt is closer to 0.6 - 0.5C. So the data in the previous post is rough at best. However, the relationship C/V remains linear 8 - 11volts (still waiting on a second DC-DC convertor to get lower voltage to the external TEC and graph the data further)

Above 11v there is no increase in differential because cooling of the copper strip to the hot side of the internal TEC has reached the optimal hot/cold side ratio, for the power ratings of the TECs and the thermal mass properties - I think?

As mentioned this set up seems to provide advantages over a brute force system, because a condition of cooling by the internal TEC is the production of heat near the camera chassis and the co-location of the TEC and sensor. I have not seen any sensor fogging as yet - localised warming near the sensor face.

I have noticed electroluminescence near the edge of the sensor in dark frames, but can't say whether this is related to the proximity of the cold plate - here (https://www.google.com.au/url?sa=t&rct=j&q=cmos%20electroluminescence&source=web&cd=5&ved=0CD4QFjAE&url=http%3A%2F%2Fwww.imagesensors.o rg%2FPast%2520Workshops%2F2003%2520 Workshop%2F2003%2520Papers%2F08%252 0Maestre%2520and%2520Magnan.pdf&ei=YfOsUdbNLOeCiQfp4YDYAg&usg=AFQjCNEJJg8ZBi30LRft-f5b2dUmFao5kg&bvm=bv.47244034,d.aGc)

[rcheshire]

The dc dc converters arrived. Seen here housed in an old webcam box, mounted on the camera base, that swings open for voltage adjustment/temperature control. The third converter will drive a dew heater. All needs testing - hoping to get out tonight and do some wide field shots.

The first image also shows the Teensy temperature test set up. Internal and external temp sensors.

[2stroke]

Dam nice work Rowland, has got me motivated to get stuck back into mine tommorow :) Grab some crops of cooled and un-cooled if you get a chance would be nice to see.

[rcheshire]

Thanks Jay. It's pointing at Rho Oph right now. At 5C ambient, cooling is off. It was running, but very light condensation became a problem. I need to plot a few more voltages for small differentials, to provide margin above dew point. That will mean winding the internal TEC voltage below 1volt.

I pleased with the low power requirements. At a diff of 12C Toal current is 1 amp or less.

It's a bit ugly in the two TEC configuration. Balance on the mount is a bit precarious.

[rcheshire]

With the internal TEC set at 1.2 volts, which seems to be its optimum and the external TEC set sequentially from 1 - 7 volts, cooling is less effective > 4 volts. Not published here, but from 8 - 11 volts cooling is ~0.5C/V, after which there is no significant benefit.

Without the external TEC fitted (that is, 0v) the internal TEC max delta is ~8C, which is consistent with the trend shown below. The only way to reduce the delta further (which would have been nice last night with cold temps and dew point near freezing), is to reduce the internal TEC voltage in 0.2 - 0.3v increments and see what gives.

The 8 - 12v data was acquired using a good quality SMPS. The reason for not including it here is that the difference between 7 and 11 volts is just 3C, using a 6amp 40 x 40 TEC. At 8 amps the delta is around 20C at 12volts - marginal at best.

EDIT: Not impressed with the latest batch of dc dc convertors. Not robust at all. 8 volts ~3 amps, rated to 6amps, burnt out. Suggest if buying these, limit input to 7 volts or provide lots of cooling.

[rcheshire]

This set up only achieves the goal of 10 - 12C differential with use of an external TEC - maximum differential is ~19 - 20C, which is suitable for warmer climates.

It may do better with a good quality internal TEC and may just trip the 10 - 12C goal, without an external TEC; however

5D MKII sensor heating, during long exposures, is considerable and almost defeats the capacity of the internal TEC - differential is around 4C at most.

Heating is required in the vicinity of the sensor face. A 5 x 10mm Nichrome anti dew strip could be attached to the plastic sensor frame where the dust reduction mechanism was attached - another project, when I pull it all apart to improve on some design issues, discussed in an earlier post.

So that's it.

[rcheshire]

This is the sensor dew heater that fits into the piezo dust reduction receptacle on the filter glass plastic frame. Made up of bits lying around with a touch of red liquid insulation and some thin wire capable of carrying the current.

6 x 100R parallel network ~20R. Voltage supply DC DC converter 0.8V upward. Hot to touch at 4V but plenty of temp control otherwise.

Images are fairly self explanatory - I think.

[rcheshire]

Further to the sensor dew heater in the previous post, the newly installed Tellurex 25x12x3.4mm TEC fits comfortably inside the space available with a very tight fit, using 1mm sheet for the copper finger, fixed to the camera chassis with 5lb external quality wall mounting double sided tape - the black and red roll found at hardware stores.

The Tellurex module though smaller, is speedy. Much faster than the standard ebay TECs. And marginally better differential at 9C @ 2.6V, without an external module to help it along - still not the magic 10 - 12.

Tellurex is ~16US, but international freight, which appears to be non-negotiable, is ridiculously high. I made other arrangements to keep the costs low.

Hope to complete assembly tonight. New moon is not far away, but forecast is rain.

A word on DC DC converters. I learned the hard way... first calculate power requirements, voltage x amps and double that to get the converter rating.

[alistairsam]

Nice work Rowland, look forward to the results.

Not sure if you've come across this, thought it might give a few ideas.
He's stripped a 450D and assembled it bare bone in a custom body for sealed cooling.
I particularly like the black silica gel ring idea and the electronic shutter simulator.
its in Croation, just let your browser translate it, if you're using Chrome.

http://filiplolic.com/cooled_canon_450d/

Cheers
Alistair

[rcheshire]

That's superb, Alistair. It would be nice to have the time... the 450D 1000D sensor assemblies really lend themselves to cooling mods.

[alistairsam]

Hi Rowland,

I still think a sealed enclosure is the way to go. so if you can somehow seal the area from the main pcb to the nosepiece, I think it'll make condesation control a lot easier.

Cheers
Alistair

[rcheshire]

I will put my mind to it. Currently in denial and employing avoidance strategies... Perhaps it's not as much work as I envisage.

[alistairsam]

hi Rowland

have you thought of using warm air from the warm side of the peltier to keep the sensor face warm?
I believe a well known ccd name uses this technique.
this video for the qhy8 illustrates this
http://m.youtube.com/watch?v=x7iEa2i4KYs

cheers
Alistair

[rcheshire]

Alistair. That was the original idea. I had high hopes, but space is very restricted. Like most of my projects, it's just a matter of time until I get a bright idea. If not, then I will redesign the whole thing and basically, start again. The concept is simple. It's the mechanics that are problematic...?

EDIT: Refering back to the 1000D cooling mod, I looked at the possibility of piping warm air, but was too impatient to get things up and running and tested.

Max differential is now -18 - camera off. So I am quite pleased with the range of control and margin to accommodate sensor warming during imaging. Tweaked the voltage on the internal TEC to improve the range.

EDIT: Bright idea! Will report back. Just needed to think about it... elementary dear Watson...

I think I have found a way to pipe warm air after all.... excited!

Work gets in the way at times.

[nebulosity.]

Just saw this and it's pretty much what I was planning for the 350d, what size TEC would you recommend for serious cooling?

Jo

[rcheshire]

Hi Jo. Serious cooling of a DSLR... I used a 40 x 40mm 15V 8A TEC achieve a max differential of 34C - 38, if you were prepared to wait an hour or so, but -30 with relative ease and control.

The size of the TEC is not the whole story. Heatsink rating is very important. Basically, for any size TEC, performance is predicated on the ability of the heatsink to reduce the temperature differential between the hot and cold side - that is, maximum heat removal.

The heatsink must also dissipate the energy used to drive the TEC, otherwise it becomes less efficient. It's not a simple formula and is also dependent on heatsink design. Passive, forced, brazed or skived fins, copper aluminium and so on.

Thermal resistance of the heatsink is another factor and possibly the best indication of performance. Low is good. If in doubt double the TEC wattage to get the heatsink capacity.

It's more about heatsink than TEC module - choose carefully. I find that TECs have a sweet spot depending on the heatsink rating and there is a practical limit to the size of the heatsink - more power is not necessarily more cooling - heating instead.

If this hasn't put you off, good luck with the mod.

[rcheshire]

This is my current solution to sensor fogging.

Inside the heat resistant sleeve is 10R dew heater. Take a length of nichrome and wind it tight around the leg of a 1W resistor. Slide the wound end off as you go and wind some more. This makes a nice little spiral heater element with a good range of voltage/heating control once stretched slightly to separate the coils.

Insert into sleeve and bend at the corners - solder a couple of thin wires capable of handling a few amps. Fixed as shown with the clear gel double sided tape from Jaycar. It's a bit tight - next version will be a tighter coil.

This works really well. A bit too good, so it needs to be run at a voltage adequate for the level of cooling.

[nebulosity.]

Thanks heaps for the info Rowland, I'll start shopping around.

I was planing on mounting the TEC on the inside wall of my aluminium case and having the heat sink on the out side, do you think that would work?
The idea was to use the case as a bit of a heat sink as well and I was hoping it might send a bit of heat around to the glass window on the front.

Thanks again
Jo

[rcheshire]

Jo. I have not built a cooler box, using cold fingers instead. TEC modules, to be efficient, like minimal temp differential between hot and cold side, when powered. Not to be confused with the sensor ambient and cooled differential. Therefore, if you use your TEC as a heater, cooling will be limited, as a result. I don't know how effective defogging will be.

However, if you locate your heatsink near the area to be heated, or connected to it, you can take advantage of the natural inefficiency of the system and/or trade off a liitle in the way of cooling performance. Rather than using the entire box heated.

My latest effort limits the degree of cooling, to a out 20, in order to avoid damage to the camera internals. To do this, I use a smaller heatsink. I am happy to achieve a working differential of 12. Reducing dark noise by 4 - half for every 6 degrees or twice the noise /6C.

[alistairsam]

Thats excellent work Rowland. very impressive.
so is the heat just radiative from the nichrome wire? or does it heat up the shield and that in turn heats the contact area on the glass?
when you say its too effective, what actually happens? does it completely prevent fogging now? so even if the sensor is exposed as it would normally be while exposing, does the heating element prevent fogging?
how about the space below the glass. won't the glass radiate heat onto the sensor face as well?

Alistair

[rcheshire]

Hi Alistair. Heating is conductive and convective. I have purposefully ensured that the element is loose in the sleeve. However, the fit is too tight in the camera and I will have to make a narrower coil to keep it all loose and minimize firm contact with surfaces.

The filter glass gets warm, tested out of the camera, and yes there will be a radiative effect to the sensor face and conduction around the edge of the filter glass sensor interface. The tape is a barrier to some extent and is not deforming - so I guess OK.

As with all this, I need to factor in operational warming of the sensor + filter glass temperature. Deicing capability will be the sum of these, rather than brute force heating applied directly to the filter glass.

It is quite brutal at 7V and defogs in an instant. At lower voltages there is a warm up time that I will need to observe. It evaporates fogging rapidly. I fogged the filter with heating off and timed the rate of clearing at room temperature and then incrementally increased the heater voltage, timing each phase. At room temperature the glass was very warm at 7v, but touchable.

Obviously, there is competition for cooling and if I could find a non-destructive way to pipe warm air, that would be kinder to the camera.

[nebulosity.]

Thanks Rowland, I drew up a quick plan to show you what I am thinking of doing.
By having the case air tight I hope to not have to much of a problem with condensation.

[rcheshire]

Hi Jo. Neat design. As you are using an airtight case can you build an evacuated chamber between the filter/cover glass and the sensor assembly. That will prevent fogging almost completely. Or just isolate the optical path and throw in a small bag of silica. I think this will be more effective than using heat from the TEC. Alternatively, duct air from the hot side of the TEC to the sensor face. Then again as the case is airtight, dry it out with silica. That should be effective, providing you can be assured of no leaks.

I guess the inside of the case will be insulated? The cold finger is a good option. Should work well.

[alistairsam]

Hi Jo,

I'll be very interested to see how you'll get the camera working without the buttons and shutter and so on.
with that 450D mod I'd posted earlier, he added a shutter emulator. I believe certain sensors and switches need to remain connected? how would you know which ones you could do without?
if you can get it working barebone with just the pcb and the sensor, then its very easy to house it in a custom case and keep it sealed. That would be awesome.

Alistair

[rcheshire]

Shutter emulator? Definitely interested. How? Thinking about dispensing with the shutter. How about a new thread?

[nebulosity.]

Cable release? Intervalometer? Yeah Rowland this could be quite a long discussion and I don't want to take over your awesome thread so I'll start another one.

Jo

[rcheshire]

Well, I've finally got this working.

Using a spare 1000D sensor, I've fitted a nichrome element in the recess reserved for the AA/UV/IR filter - resistance = 7R7 as it happens.

Testing - I started by cooling without the dew heater running and predictably the sensor face fogged up badly.

Powered up the dew heater, starting at 1V, incrementing by 0.5V to 5V. Dew began to clear at 3.5 - 4V, but not completely. At 5V no dew.

The heater element needs to be aligned with the inside edge of the plastic frame, as shown to be effective. Made a small adjustment on one side to move element closer to edge, which had an immediate effect clearing that side of dew.

Second test - started cooling with dew heater 5V - no sign of dew. To be expected. At 5V the element is working overtime to clear an accumulation... etc etc

Third test - started cooling with dew heater at 4V - no sign of dew. Speaks for itself really.

Given test observations and the high thermal resistances involved because of the use of plastics, condensation prevention seems to be due to radiant heat and to a limited extent, conduction. The heater was only successful when an edge of the element had line-of-sight to the sensor face.

No doubt there is a trade off with cooling, but not equivalent to heater power. Yet to do a temperature test.

The best way to install the element is to attach it to a very thin, rigid plastic frame, in place of the AA filter. The element hangs below the frame and is removable. If the AA filter is retained stick the element to that. But you will most likely need to remove the piezo device to get things to fit. Wiring is very tight.

To fabricate the element, which is 3mm wide and 1mm deep, wind nichrome around a 2mm drill shank - tight - no gaps in the coil. Drop the coil into a bench vice - again, keep the coil tight and support in the vice with a 1mm straight edge. Tighten the vice to clamp the straight edge. When released from the vice the element will twist. This all but dissapears when stretched. Depending on requirements, stretch to say, 0.5mm or 1mm spacing, depending on sensor size and target resistance.

I have aimed to keep voltages low. It might be necessary to strip the supply leads back far enough, to clear the sensor assembly - insulate with heat shrink to keep as thin as possible.

Nichrome is difficult to solder. I run a fine grit over the ends, then wind onto the ends of the supply lead and solder- minimal.

144 turns of 0.32mm nichrome = 12R - element width = roughly circumference of drill/2 and make an allowance for wire gauge.

[rcheshire]

With this little test rig, the temp differential ran to ~20C with a 12V 6A TEC and 4.8V applied to the 7R7 sensor dew heater, which is hot to touch, but not burning. I can live with that. Cold finger temp was -2.15 ambient 17.7.

I dropped the dew heater voltage to 4V - at -1.5C the sensor started to fog up. Increased to 5V, clearing in 5 minutes, with an increase of 1.5C cold finger temp. 4.8V seems to be the spot, evaporating light introduced condensation in about 5 - 10 seconds.

Given that this was an open air test, defogging should be more efficient with the sensor in the confines of the mirror box/rear telephoto lens.

For me - Myth Busted. Let's see how it works in the field on a cold night - might need to wind the TEC voltage back a little. -5C is adequate. Watch this space.

[nebulosity.]

Great job Rowland :thumbsup: hope you get some awesome results.

Jo

[rcheshire]

Thanks Jo. I did overtime on this one, but it was worth the trouble. Nice to look down the barrel and see a fogless sensor, with the cold finger at -3C. It works in camera to roughly the same specs as the test rig, with -22C diff. Hardly budged taking a 3min dark. The 8amp TEC is a beast - tempted to try it... hmmm... No! Leave it be... Next is to translate that all to the 5d mkii.

EDIT: -7C cold finger and no condensation on sensor face. Consistent 19.5C differential. No change over 3 min exposure.

[2stroke]

Great work man :) my 1100d died after the dam brother inlaw moved it from the desk i had it on uncased, so my project is at a stop till i get a 4th 1100d haha Your inspiration has cost my pockets dearly lol.

[rcheshire]

Last post was lost.

You probably have enough parts to build a working camera, Jay. Keep it simple. The sticking point for me was sensor defogging, but it looks like I have that under control now.

Really, the benefits of deep cooling for a 1000D or 1100D are limited, because Canon has managed to keep the dark noise low, to a point, after which it is exponential. If you can get your sensor down somewhere between 5 - 10C, any lower has marginal benefit.

The 5D MKII on the other hand benefits enormously from cooling, because the sensor temperature escalates to ridiculous levels with long exposures. Measured externally, bottom left hand side of the sesnor frame, even with cooling the sensor is 5C warmer when exposing, than the camera on temperature, which is 3C warmer than camera off. It's a beast. But cooling to -5C - 0 is adequate.

Have fun. Maybe we should have a workshop to reclaim some of the collateral.

[rcheshire]

I took advantage of the cold rainy night, here in Geelong, to further test the newly installed sensor defogger, fitted to my test camera, in addition to installing an Astronomik EOS UV-IR Clip-in filter, which reduces the volume of air in front of the sensor. Using a spare sensor, I did a full spectrum mod with the intention of fitting a clip-in.

I have migrated the cooling and sensor defogger to a 1000D test bed.

Cold finger temperature -10.94C, with sensor defogger set at 4V, slight condensation appeared in the bottom right corner of the sensor, but not enough to infringe upon the active portion. A slight increase in voltage will fix that. Normally running the defogger at 4.7 - 4.8V.

Very happy with this result. It is unlikely that these sorts of temperatures will be a regular thing and the test camera is working just fine. Then again for summer cooling I'm tempted to work on a more efficient setup, with a bit more aesthetic appeal.

I'm not sure if anyone is getting anything out of this? But my research indicates that one of the most ideal candidates for this set up is a 450D. 14 bit, pixel size 5.2um, same as 1100D, characteristically low noise and construction almost identical to the 1000D, which makes it a breeze to convert and cool. And a biggy - very cheap second hand.

I'm not taken with the 5D MKII as a candidate for coolling. Like many of the latest Canon offerings the sensor heats to astronomical proportions by comparison to earlier models that I have looked at. It is not very robust either. I find it too delicate/ fragile and ready to malfunction. But I do like the image scale with a 200mm lens.

In short, unless you are prepared to live with a bit of pain, mod something else. A cold finger, electric sensor defogger and a couple of good quality adjustable DC DC converters is all thats needed.

[gregbradley]

I wonder if you could make a little housing for the sensor and put in a desiccant plug which are available for SBIG cameras. That's what they use to allow cooling without dew and condensation.

Adding some argon would help too.

Greg.

[rcheshire]

Hi Greg.

That is probably achievable by fitting a glass cover in place of the AA piezo filter and some way of purging the cavity. That would be a straight forward solution at a squeeze. Design philosophy is minimal intervention. I'm not convinced of the reliability. I notice on some sbig cameras a small heating element.

[alistairsam]

Hi Rowland,

I came across this EOS adaptor that accepts 2inch Filters.
I think this could be used to act as a humidity seal by adding silicone around the clear glass filter so sensor wouldn't be as exposed.
this doesn't add any backfocus either.
http://www.baader-planetarium.de/sektion/s17/bilder_protective/eos-body-gross.jpg

they also have a similar one with a UV/IR glass.


http://www.baader-planetarium.de/sektion/s17/bilder_protective/basis-filter-gefasst-gross.jpg
http://www.baader-planetarium.de/sektion/s17/s17-en.htm

https://www.teleskop-express.de/shop/product_info.php/info/p5913_Baader-Protective-Canon-DSLR-T-Ring-with-Clear-Filter-to-protect-the-sensor.html

Alistair

[2stroke]

Myself and wife grabbed a starshoot pro v2 color aka qhy8l the other day man, lol 3rd 1100d so i've given up as its adding up to much now for experimental fun. Might see what she wants to do and may just pass onto you to tinker with instead of the bin lol, the 3rd 1100D has the noise issue which a far share of CN user have had and will just use now for a time-lapse/ lighting cam. The first cam is stripped down into pieces after i thought it was dead (Always check the battery door switch ROFL), second cam wont open shutter or something bro in law plonked it in a box with no casing when i was working on re-house AHHHHH!!! So now i'am just moving onto the ccd path so i can get back to what i enjoy without being stuck with an un-modded cam.

Have to start now on getting my second st80 collimated and maybe a rehouse of the dsi pro to shave some weight off the guide system and fix the dam flexture issues we are having. Next real project will be building a portable pc with some juiced up usb 3 ports as running 2 notebooks is getting a bit sad and i really need 2 screens. I also need the full bandwidth of usb 2 on the dsi and imager along with amps.

[rcheshire]

Thanks Alistair and Jay. I've moved the experimental work to a 1000D, because they are a no brainer and easy to play with and added an Astronomik uv/ir clip-in to correct the full spectrum mod, which seems to have improved the performance of the electric defogger. I want to follow this through and test it over several nights of high humidity. Though it seems to manage a cold finger temp of -5 -7C OK. Drier air -10C.

I am accumulating second hand cameras for parts at an uncomfortable rate. 1100D sounds interesting, but I have a 40D to do first.

I am not pursuing the 5d mkii until I have more data. These cameras are perhaps the least robust, in my experience.

I am also testing an improved pwm system that seems to be quieter than other designs I've tried.

I do this stuff out of curiosity. It's fun and interesting. As I get older, the late nights imaging are not compatible with my line of work. I can't afford the fatigue levels. So this keeps my interest between star parties.