Canon DSLR cold finger fabrication

[Camelopardalis (Dunk)]

Thanks Glen, that's a great reference! I just hope I don't Bork my shutter

Btw, is there a preferred TEC module?

And what are you guys using for powering it?

[AlexN]

I'm using a 40x40mm 12v 60watt TEC powered from the same 12v psu that runs my mount, dew heaters, focus controller etc. I also have a 12v to eos adapter that powers the camera from the same 12v supply and a 7v step down module to power the fan (lower rpm = less noise and vibration.

[AlexN]

Ps Dunk, I've run my 450D with no back panel on it. Works fine but leaks light bad. Think fish tank made of fly wire.

[glend (Glen)]

Dunk, not trying to bury you in information but you might find this guys approach interesting:

http://www.singastro.org/forum2/view...hp?f=8&t=10936

[ZeroID (Brent)]

Just been catching up on this. Hadn't even thought about this idea.

One design thought I've got bouncing around is that the rear screen is essentially redundant these days as the camera is always tethered to my laptop, so is there any sensing logic in the camera that makes it non-functional if the screen isn't there?

What I'm thinking is that if I remove the screen then a large hole suddenly appears in the back of the camera, and I can get away with a smaller cold finger, just a U-shape from the sensor and bending where necessary to present itself at the screen-free aperture at the rear. The TEC and heatsink/fan can then be attached there.

Possibly, if required, it should be possible to mount the screen away from the back, right angles or something or as you say, remove it altogether. That really simplifies access and fits better with my copper slab idea. I going to HAVE to find an 1100D now. Hobby finances are steadily recovering so maybe soon...

[glend (Glen)]

I would have one caution about removing the back - it provides some shielding and is earthed to the camera chassis. Any swing out screen model might be a better choice for a rear mounted cold finger as you,d only need a slot for the finger to exit through.

[Camelopardalis (Dunk)]

Originally Posted by AlexN

I'm using a 40x40mm 12v 60watt TEC powered from the same 12v psu that runs my mount, dew heaters, focus controller etc. I also have a 12v to eos adapter that powers the camera from the same 12v supply and a 7v step down module to power the fan (lower rpm = less noise and vibration.

Thanks Alex - sounds like the direction I was heading in, as you can always turn the power down Any suggestions for a source of these and heat sink / fan type parts in the Brisbane area? I like to walk in and size things up when it comes to this sort of thing.

Originally Posted by AlexN

Ps Dunk, I've run my 450D with no back panel on it. Works fine but leaks light bad. Think fish tank made of fly wire.

Thanks again - my plan is to have the heat sink mostly blocking up the gap where the screen once was, and seal it around with rubber or silicon. Nothing firm, just thoughts right now

Originally Posted by glend

Dunk, not trying to bury you in information but you might find this guys approach interesting:

http://www.singastro.org/forum2/view...hp?f=8&t=10936



Thanks again Glen - you can never have too much information, only too little

[Camelopardalis (Dunk)]

Originally Posted by ZeroID

Possibly, if required, it should be possible to mount the screen away from the back, right angles or something or as you say, remove it altogether. That really simplifies access and fits better with my copper slab idea. I going to HAVE to find an 1100D now. Hobby finances are steadily recovering so maybe soon...

My thoughts are to be as non-invasive as possible. I'm not using the screen at all in practice. I also want to strip the mirror out. But besides that I'm OK with the size and weight, actually I find it convenient in its compactness. A screw driver and some tape and silicon I think I can handle, fabricating a new box not so much

[rcheshire (Rowland)]

Recommended a roll of black duct tape on hand - good for fixing light leaks.

No need to go too cold, but a smaller cold finger will likely reduce power consumption.

[glend (Glen)]

With a number of IIS members talking about commencing work on a cold finger mod it is timely to point out the wealth of information buried in this thread on IIS, you just need to go back in time to find it here. For example, the work done on a low cost set point temperature controller and TEC power management system is covered in this thread. The box that I built out of an ebay 12V temperature controller and a PWM (total cost about $30) has served me well for some time now and will be used on my new Mono DSLR as well. It doesn't require a knowledge of electronics to build as it uses readily available parts, if you can wire up 12v supply for your various astro equipment, you can build the set point temperature controller/TEC power management system.

Re the TEC itself, a standard (#12706) TEC which is 40x40mm is sufficient and cheap. It draws only 6 amps but is good for a delta T of -25C at full power. As we know, it is possible to get good low noise performance out of a 450D sensor at 0C, so don't worry about trying to get down to below -5C as your chasing improvements at the cost of other potential problems (frosting, etc). In summer night time temps (say 20 - 25C) this TEC will do the job on full power, and in winter you can throttle it right back to your setpoint. If your facing night temps of greater than 25C then the next TEC up (which draws 8 amps) might be worth considering if you can power it.

I am still happy with Argon bagging as a way of eliminating condensation/frost issues but it can add a dimension of complexity and there are other ways emerging now that I want to investigate as well. The dessicant silica paper strips used in GoPro camera enclosures are promising, and low cost, readily available locally, and they are also rechargable and can fit inside your camera in various places.

I have done a lot of reading on this subject on all the forums, and without a doubt (IMHO) this thread on IIS is the definitive and best source of information on the topic, and backed by examples from people that have actually done the work and use a cold finger camera in the field. I thank Rowland for all the work he's done on development and promotion of the solutions, and the continuing inspriational work on the electronics side of things (far beyond me most of the time).

So for you guys thinking about it, don't be scared to give it a go, plenty of support here to help you out. Just go back and review key points in this long thread to work out what you can use or learn from.

[rcheshire (Rowland)]

Here is a link to a temperature control circuit, which is far less complex and cheaper than the micro controller setup. Using the separate operational amplifier channels all the main cooling and heating features of the micro-controller can be inexpensively implemented with a single chip and good power supply.

http://www.iceinspace.com.au/forum/s...59&postcount=1

[Camelopardalis (Dunk)]

So...quick question...it's been a long long time since I did any circuitry...for a crude test, is there any reason I couldn't just use a potentiometer to control the current to the TEC? Obviously I don't want to burn through power that may be limited at a dark site.

[glend (Glen)]

Originally Posted by Camelopardalis

So...quick question...it's been a long long time since I did any circuitry...for a crude test, is there any reason I couldn't just use a potentiometer to control the current to the TEC? Obviously I don't want to burn through power that may be limited at a dark site.

Dunk, I would suggest this is a better choice, and it gives you the control you seek for $3.79:

http://www.ebay.com.au/itm/HOT-New-P...sAAOxy3NBSfIUR

I use this exact device in my control box. You don't need to run it through a temperature controller, simply dialup the power you want with the pot. It's rated to 10A and you only need 6A for the TEC. Just 12V input and output goes to TEC + & -.

There are others available already mounted in boxes.

[rcheshire (Rowland)]

Originally Posted by Camelopardalis

So...quick question...it's been a long long time since I did any circuitry...for a crude test, is there any reason I couldn't just use a potentiometer to control the current to the TEC? Obviously I don't want to burn through power that may be limited at a dark site.

Do you mean directly through the pot...?

Glen's 12v pwm motor controller would be a safer option.

[Camelopardalis (Dunk)]

Thanks guys! There will be undoubtedly lots more questions

What's the significance of the frequency with a PWM, in a practical sense? Is it just the frequency it's pulsing the current on/off? (I'm guessing about this!)

[glend (Glen)]

Originally Posted by Camelopardalis

.....What's the significance of the frequency with a PWM, in a practical sense? Is it just the frequency it's pulsing the current on/off? (I'm guessing about this!)

Dunk, basically yes your right. From my limited knowledge of the electronics involved, the frequency refers to the switching frequency. The longer the duration (width of the pulse) of the circuit being on, the higher the total power supplied to the load, the shorter the duration the lower the power supplied to the load. Importantly the switching happens so fast that it does not affect the operation of the load device.

Full details here: https://en.wikipedia.org/wiki/Pulse-width_modulation

Clear as mud right?

[Camelopardalis (Dunk)]

Thanks Glen, I think I get it.

I'm considering this one: http://www.jaycar.com.au/Power-Produ...oller/p/MP3209

Mostly because I can get hold of it quickly...not a big fan of waiting for weeks for stuff to arrive from overseas and causing a bottleneck. Obviously, that costs extra.

I'd like to dabble with something like arduino control, but baby steps

[Visionary (David)]

Originally Posted by Camelopardalis

Thanks Glen, I think I get it.

I'm considering this one: http://www.jaycar.com.au/Power-Produ...oller/p/MP3209

Mostly because I can get hold of it quickly...not a big fan of waiting for weeks for stuff to arrive from overseas and causing a bottleneck. Obviously, that costs extra.

I'd like to dabble with something like arduino control, but baby steps

Neat, the best solutions are always the solutions that have been previously worked. I think I maybe placing an order for this little baby. Great idea.

[ZeroID (Brent)]

OK, got fed up trying to buy a cheap second hand camera on TradeMe. Local dept store was having a 20% off sale so picked up a new 1200D single lens kit for $500, only $50 -$70 dearer than what was being asked for 450D-1100D bodies only.

Plan is to mod the 450D for IR and possibly cold finger and use the 1200D for imaging then mod that later. In the meantime I gain more pixels and ISO with a newer low noise sensor plus a Canon lens (18 -55 ) which I was also trying to buy cheap for testing later.

Time to clear some bench space downstairs

[Camelopardalis (Dunk)]

Sooooo.....my 1100D is now a box of puzzle pieces

I stripped it down to first tackle the colour filter and with glue now drying I'll refit it over the sensor tomorrow.

Having it all apart and poking around a bit, the cold finger looks like it's going to be an interesting challenge of dexterity as there are a couple of nubs and screws that anchor the assembly to the main frame that will need to be navigated by the cold finger.

At this point, I've already scrubbed my original objective of making it all fit back in the original Canon case. Now I've looked at what else can be rationalised from the unit it hardly makes sense, and a small plastic box should suffice, with holes in the right places. I was actually thinking along the lines of a tupper-style container (in dark opaque of course) with a lid that could be peeled off to change desiccant, although I expect I'll go for whatever is cheap and whatever is available