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Adding cooling and filter wheel to a debayered 450D mono DSLR


Gina

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Those dark frames look pretty respectable already Gina - I take it from the following post that these are uncooled taken around room temperature.    Even with the cooling switched off are these better than an unmodded 650D (ie does it dissipating heat better with the passive cold finger and open case)?

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Those dark frames look pretty respectable already Gina - I take it from the following post that these are uncooled taken around room temperature.    Even with the cooling switched off are these better than an unmodded 650D (ie does it dissipating heat better with the passive cold finger and open case)?

Thank you Jake :)  Yes, these are at room temperature with passive cooling only.  The open camera was placed on the carpet and covered with two cardboard boxes with a weight on top of the outer one to keep the light out.  I tried it with all the house lights out but the sensitivity was such that I got an almost white image with the CFA border distinctly visible.

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More progress on the cooling.

Peltier TEC on cold finger.  Also shows earth wire for cold finger to prevent interference.
post-13131-0-99029000-1381428761_thumb.j

Polyether foam thermal insulation all round the cold parts and TEC.

post-13131-0-45646700-1381428767_thumb.j

CPU cooler fitted to copper dry chamber box

post-13131-0-80816600-1381428771_thumb.j

M3 Allen screws through the copper box into tapped holes in the copper part of the cooler hold the cooler in place.

post-13131-0-36498600-1381428789_thumb.j

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Further progress to make the camera body all fit in the dry chamber. 

None of the top parts of the camera are needed for astro imaging other than the ON/OFF and Mode switches, so I've replaced the Mode and ON/OFF combined function switch with blobs of solder on the gold plated ribbon cable (the part that acted as the switches in conjunction with sprung contacts).  The solder connections set the mode to "M" and power to "ON" - all other functionality is not required and the rest of the ribbon was snipped off.  This means that the whole top section of the camera is reduced to just one small piece of ribbon cable.  I insulated the soldered bits and ribbon surface with insulating tape and attached the ribbon to the battery box with double sided foam.

These photos show the modified ribbon "switches" and the resulting much more compact camera body.

post-13131-0-55661700-1381441583_thumb.j  post-13131-0-17402600-1381441589_thumb.j  post-13131-0-53797900-1381442833_thumb.j

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Very neat job Gina - look forward to seeing the new darks.

Thank you Jake :)  I'm afraid I'm not yet ready to do another darks run.  I have not yet got the imaging section light tight and the cardboard box method won't work with the Peltier cooling running as the heat would build up in the enclosed space.  I had forgotten that. 

A couple more things need doing before I can enclose the camera body.  I need to attach wires so that the camera can work without the battery and close off the top of the box (dry chamber).  I'm hoping to get that done tomorrow.

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More photos...

Power supply wires soldered onto power board plus ceramic capacitor to prevent RFI getting in

post-13131-0-40235100-1381493725_thumb.j 

Top of battery compartment cut off to fit better in the box

post-13131-0-62656200-1381493729_thumb.j 

Part of the main plastic frame cut off to fit in the dry chamber

post-13131-0-58595700-1381493735_thumb.j  post-13131-0-47702800-1381493739_thumb.j

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Problem :(  Caught the shutter and now it's not opening so I'm going to have to strip the camera down and examine it.  I think I have a working shutter I could put in if necessary.  Curses!!! :(

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Think I've found the problem and hopefully cured it - a shutter blade was stuck against the frame so I freed it.  Now (after a cuppa) to put the camera back together and see :D

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Everything is working with the camera in the copper box, powered from my bench PSU.  I'm running APT on my netbook with a sequence of "Darks" of 1m, 2m, 3m, 4m, 5m.  I've put a cardboard box over the top (I'm not powering the Peltier TEC ATM so only heat from the camera).  There's some light getting in so these are more like flats or lights than darks.  Actually, this is more representative of how the sensor is working that either daytime lights or darks.

Next job is to make the required holes in the aluminium plate and screw the angles that hold the copper box onto it.  I might manage some of that this evening.  The big hole for the light path will have to wait until tomorrow as it will require my bench drill and trepanning tool, out in the shed but I can drill the holes for the wires indoors.

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Here are the processed exposures - moderately dark :)  Ps curves stretch x10, x5 and -10% (light slider moved to 10% = x10 and saved then light slider at 50% = x2 and dark slider to 10%)

post-13131-0-75725500-1381517788_thumb.j  post-13131-0-73959400-1381517790_thumb.j  post-13131-0-14234900-1381517793_thumb.j  post-13131-0-86537300-1381517797_thumb.j  post-13131-0-86113100-1381517800_thumb.j

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Last night I set up the camera in the copper box on a mat on the table cooler upwards with a weight to hold the assembly down against the springiness of the cold finger leaving less than a mm gap between the copper box and the mat (sorry - no photo).  I ran the 12v Peltier TEC on 5v and the cooling fan on 12v from an ex-PC PSU and the camera from my bench PSU at 7.6v.  The sensor was cooled to the point that severe condensation formed, yet the EXIF T showed 21C.  I don't know what the cold finger temperature was because I haven't yet connected up the digital thermometer.

This is a 5m exposure at ISO 1600 - stretched as above.

post-13131-0-04180300-1381568353_thumb.j

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Decided to turn off the cooling leaving just passive cooling without even the fan running and do a longer run with all the lights off. monitors turned off and the bench PSU display etc. shielded from the camera area to reduce the ambient light level as much as possible.  Then I set up to control the netbook from my bedroom MacBook with TeamViewer, to keep the light in the lounge to a minimum and set up a run of 300, 420, 600, 900, 1200, 1800, 2400 seconds (yes one whole hour!).

Here's the results - CR2 > TIFF with DCRaw, processed in Ps as previously.  The 60m one showed considerable white clipping with that amount of stretching but the noise can still be seen in the border where the CFA remains and the sensitivity is less.

post-13131-0-81319700-1381571328_thumb.j  post-13131-0-07548400-1381571334_thumb.j  post-13131-0-72410400-1381571337_thumb.j  post-13131-0-38145100-1381571341_thumb.j  post-13131-0-14800000-1381571345_thumb.j  post-13131-0-97280000-1381571348_thumb.j  post-13131-0-98646700-1381571351_thumb.j

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I find I need to order some more screws before the main construction can continue so I'm now looking at the Arduino control system.

Previous DSLR set point cooling systems used a large variable speed cooling fan but this time I want to reduce the size and weight of the finished unit so I'm using a smaller CPU cooler without variable speed.  The latter was unnecessary in this application - no need to reduce speed and noise from the fan.  The other major change is that the cooling will no longer be controlled from a box on the mount but only from the computer, reducing the hardware and Arduino sketch functons.

Previous cooling solution used these modes of operation :-

  • 0 - All Off
  • 1 - TEC Off, Fan Full
  • 2 - Gradual Warm Up
  • 3 - Set Point Temperature
  • 4 - Dew Point + 2C
  • 5 - Dew Point + 1C
  • 6 - Maximum Cooling

This will be reduced to :-

  • 0 - Off
  • 1 - Gradual Warm Up
  • 3 - Set Point Temperature
  • 4 - Advanced settinngs

The "Advanced settings" will be for development and may be removed later.   I may make the actual user interface like the Atik with settings of Cooling or Warm Up (Off when warmed up).

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Hardware-wise I'll be using a power MOSFET to control the Peltier TEC (a higher quality item this time) and the sensors will be the cold finger digital thermometer and a DHT22 digital humidity sensor for the dry chamber.  The latter will be used to calculate dew point for the sensor (actually the cold finger - the sensor itself will be very slightly warmer).  I've had problems in the past with keeping the dry chamber dry enough - I hope to have cured that in this version.

An addition with this DSLR is a filter wheel which will also be controlled by the Arduino.  In a previous home made FW I used a stepper motor plus a single micro switch to detect the HOME position but I may use a DC motor with friction drive in this one and use an optical encoder to detect the position.  The stepper needed 4 control pins plus 1 for the micro switch - a DC motor would use 1 pin for motor control and 2 for position sensing.

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Looking into the filter wheel and various measurements.  The optical path has been reduced by 15mm - from 44mm to 29mm.  The aluminium plates I have for the FW casing are 3mm thick and the carousel is 5mm thick.  For M42 thread lenses I could use an adapter (M42 to EOS) like I have on the widefield triple imaging rig.  That has a 1.3mm thick flange - the difference between the back focus of the Pentax/Praktica cameras and the EOS range.  The overall thickness is 7mm but that could be reduced by the use of a hacksaw :D  However it wouldn't help because the Pentax type lenses project into camera by about 7.5mm from the reference surface (that's about 6mm in from the outside surface of the FW casing.  The filter wheel casing therefore will want to be 15mm overall and the inside space will be 9mm.

Here's the overall picture.

post-13131-0-09703900-1381681329_thumb.p

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From this it can be seen that there would be no room for anything other than rim drive for the carousel.  I have no accurate way of cutting teeth on the edge (yet) so I will be using friction drive.  I'm thinking of using a modified (for continuous rotation) micro servo motor with some sort of spring arrangement to hold the shaft against the wheel.  I will perhaps need to confirm it but I believe this will stop the carousel "dead" as soon as power is removed.  Therefore I plan to just use a transistor to control the motor with ON/OFF control from the Arduino.

Position sensing will be with IR photo detectors.  As there will be 4 positions, 2 bits Gray code will determine the position.  Rather than 2 tracks I shall use one track with the sensors spaced at 90 degrees round the edge.  Transmission sensors would (no doubt) be best but in view of the limited space I'll probably use the reflection type.  The phototransistor contained in these will drive the Arduino digital inputs directly with the internal pull-up resistors.  The IR emitting diode will just need a series resistor.  I may power these from the Arduino and turn on emission only during the filter change phase to avoid any possibility of IR getting to the sensor - though I think this would be blocked by the IR/UV cut filter being used as the optical window.

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Could use a rubber band around the outside of the filter wheel and the motor.

Yes, I could - if I filed a groove in the edge of the wheel so that the belt didn't work it's way off.  I agree that would be easier :)

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In fact a round belt with semi-circular groove was what I originally planned for my no.2 ED80 DIY filter wheel before changing to centre drive with timing pulleys and belt.  The wheel is acrylic so I can quite easily file a groove in the edge with a rat-tail file.  I guess I could ease the job by mounting the disc on a bolt and nut putting it in the bench drill :D

I think your idea is better than a friction drive, Nick (even though Atik use friction drive) :)

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Hi Gina,

I've followed most of your threads about your DSLRs transformations (qualified as "butchery" at the begining), being busy myself with the mod of a 1000d to have thermoregulation and as light as possible in a home made enclosure. I have one question regarding this mod : I was wondering myself if I would or not cut the plastic pyramid on which the bayonet is fixed in order to reduce the optical path length. But I ended up deciding not to do it to be sure not to introduce "tilt". I see that in this mod, you decided to cut it. How do you ensure to have the sensor parallel to the focal plane (not having tilt) ?

And a second question also, if I may : is the shutter really needed ? 

I was happy to see you could cut the ribbon from the top, I was wondering if I could do it on the 1000d too, I had the feeling it was really not necessary. I try to eliminate everyting I can : I even removed the battery compartment and the CF reader PCB, the flipping mirror, ... 

Ah, one more question still :  what capacitor to add to the power supply connection to eliminate noise ?

Clear skies, wonderfull nights and alot of fun while busy on your projects !

Mike

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