Luka there are no drawings of the bracket, i made each one to support the finger and each of the two fingers are slightly different. On the mono camera, which was made after the colour camera, the finger bends closer to the camera, so each bracket is (as the Brits would say, "bespoke" engineering). I just start by cutting the base out and then sit a piece of carbon fibre flush against the finger and mark the base. Tack it in place with some five minute epoxy, then put the good structural epoxy on later with the bracket on the bench. Final trimming and edging is done late.
A humidity sensor would be a good option but i have not felt the need for one yet. I have some dessicant packs inside the bag and of course it gets an Argon top up before each session. Rowland (rchesire) is the electronics wizard, i prefer using simple circuits like my remote controller box. If you come up with a humidity alarm then let us know about it.
Regarding bag sealing, i tend to rely on pvc duct tape, it also holds my cold finger insulation in place. However, sealing around cable exits, and the bayonet/t-thread adaptor are the critical points. You will need to exit your usb cable, your power cable (must use a battery eliminator), the temperature sensor that goes to the setpoint controller, and the humidity sensor if you put one in. A single exit for them might be a better choice than separate ones.
Sealing the bag around the cold finger is also a problem but i have changed my original bag design so that the bag us now taped to the bracket insulation all the way round, this is much easier to change if required and does not require any disassembly to change the bag.
I finally got most of the parts and some time to disassemble the 450D and to start planning how to do things.
What thread size are the two nylon screws that attach the copper finger to the sensor assembly? Are they just M2 (don't have any here so I cannot measure before ordering).
In the no-step design, did you use spacers for those screws, between the copper sheet and the sensor? What height? Or to rephrase the question, is the sensor height 2mm? It looks around 2mm but it is quite hard to measure exactly.
Edit: Found the answer in one of the cold finger threads, it is 2mm.
Yes Luka i used 2mm nylon spacers, and you may need to cut the screw heads slightly to avoid them getting caught on the board edge. The good thing about nylon screws is you can melt them on the edge if you need to. You need to watch the clearance under the nut on the bottom under the finger, you don't want to have the finger high sided on the nut againt the frame. On my colour camera i drilled a counter sink hole in the frame But you need to remove the frame from the camera to do that, not easy. On the mono camera i just melted the end of the screw shaft with a soldering iron to turn it into a nylon rivet, and that had no clearance issues. If your not bending the cold finger like Rcheshire's pattern, but carrying it straight out the side, tere will be no bottom clearance issues. Re screw size i think i used 3mm at least on the one i turned into a rivet. Bought the nylon hardware from a RC (radio controlled model), online shop located in qld.
If you run the cold finger straight out you will need rest it on a spacer attached to the frame, i used a carbon fibre spacer on my mono camera, made of 2 small pieces of 2mm carbon sheet epoxied together. You just need to experiment with what size you gap is.i put double sided auto trim tape on the spacer to bond the finger to the camera frame. All of this is 'bespoke engineering' so just do what is right for your version. I hope you remembered to insert thin plastic strips down the sides of the cold finger where it passes behind the sensor, this is important to keep the finger from moving side to side and even more important, it keeps the finger from shorting againt the sensor pins, which could kill your sensor.
Good luck.
I have some images up on Astrobin now from the mono camera. If you care to have a look just follow the link below (there are few in the top row of my public gallery). Be aware that I hate the processing side, and this narrow band stuff would surely be done better by a pro but its a first step.
Four of the images on the top row of the gallery are from the mono camera, in narrow band.
Nice images Glen, especially considering you are just starting in narrowband processing.
What I would really like to see is the comparison between these DSLR images and your soon-to-be-arriving ZWO mono camera. Any chance you could try to replicate the imaging parameters of one of these images with the new camera and compare the results?
Yes Luka i can revisit the same targets for a side by side comparison but it may not be an apples to apples comparison. Realistically they are very different.
I can announce that my mono, cold finger, Canon 450D is now for sale. I need to let it go to pay for the new camera development i will put an ad up in the classified section later today. It is hard to establish a fair price for it given the add on equipment, the development hours, etc but i will try to be reasonable about its worth in dollar terms. Stay tuned.
As indicated below, I am selling my Canon 450D (mono, cold finger setpoint cooled) camera, featured in this build thread. The ad is up in the IIS Classified section here:
Did you guys use a clear glass in front of the sensor, something like Astronomik MC clear glass? Where did you get the glass from? I could not find it anywhere in AU.
Also I hope your DSLR sells Glen. As you said it is hard to put a price on it and most of people cannot appreciate all the work gone into it. Personally, I like the challenge of doing it myself... which is much easier now thanks to the pioneering steps you guys did.
Yes Luka i used an MC Clear coverglass over the sensor, and i sourced it overseas from Astonomik directly. I also have another MC Clear barrier by way of a Astronomik MC Clear EOS Clip-in filter in the mono camera, which is sealed in place to provide an argon chamber ahead of the sensor. However, i would not exoect everyone to go that far in condensation protection. Because i am imaging from my observatory, i need the camera to be able to run for six hour sessions, and keeping the optics clear is a necessity.
On long imaging runs I do sometimes run into a problem with cold soak, where the cold transfers through the scope adaptor to the front mounted UV/IR Cut filter. The front filter is exposed to the atmosphere and can get some fogging on it. Inside the front filter is the argon chamber so it can only fog on the outside. The answer would be to heat the external facing adaptor filter but i never got around to that, i have used a heater strap wrapped around the focuser barrel to transfer heat to the camera adaptor barrel, that seems to work ok.
Rowland worked on a couple of internal heating approaches in his thread, worth reading.
I ducted a small stream of warmish air from the TEC output fan and radiator across the face of the window. Piece of soft rubber tubing jammed into the fins and trapped in a convenient slot in the tube extender worked extemely well.
You would build some really flash option with valves etc I'd guess knowing your build doctrine, I just use some rubber tube ...
But yes, hard to put a value on a DIY project of that nature.
I would like to close this thread down now and let it go to the archives. I have retired the mono cooled 450d and since it has failed to sell here in the classifieds it will probably be broken down for parts and sold off on ebay. I have not given up on mono imaging but am shifting to my new ASI1600MM -Cool camera which i am testing with now.
I have enjoyed the development of the mono cold finger 450D and i believe i have demonstrated what it is capable of achieving in narrowband imaging. Your welcome to check out my Astrobin gallery top row for the narrowband images from the 450D.
Luka i think you need to start your own build thread now, and i will be there for advice if you need any help.
Thanks to everyone that stopped by this thread with encouragement, advice, and good wishes.
