Debayered and Cooled 1100D

[Gina]

This is my latest project and I expect will be highly experimental

Following on from the thread on Debayering a DSLR I have developed a renewed interest in playing with DSLRs for astrophotography. This is starting as an experiment to see what I can achieve but if the results are good enough it may become a quite usable astro camera.

The specification I am aiming at ias as follows :-

1. A debayered sensor converting the DSLR from an OSC to a mono camera.
   
2. Set point Peltier cooling to -15C
   
3. Reduction in optical path length to permit using a filter wheel and still maintain the 55mm back focus required for focal reducers on telescopes.
   
4. A sealed enclosure with moisture reduction to enable use of -15C sensor temperature without any condensation or misting up of any optical parts.
   

Item 2. I have already achieved and item 4. to an extent in that misting would not occur for a week or two. I am currently working on item 1.

[Gina]

1. For details and photos of my attempt to debayer a duff sensor see the Debayering thread - http://stargazerslou...x/page__st__600
   
2. For details and photos of my previous 1100D cooling see - http://stargazerslou...v3/page__st__40 This thread also lists links to my earlier excursions into DSLR cooling near the beginning.
   
3. I've stripped the camera down further and I reckon I can gain 15mm in back focus. There will be a small problem of getting the focal plane of the sensor accurately orthogonal to the optical axis.
   
4. This will depend on how thing go with no. 3. above. The camera case will consist of two compartments I think. An inner one containing the sensor and some camera parts that will be sealed and dehumidified and an outer one containing other components such as the Arduino, voltage regulator and maybe a filter wheel.
   

[Gina]

Here are some photos.

The sensor unit exposed ready for removing the cover glass and debayering.

Views of the Peltier cooling.

These photos show the amount of space available to reduce the optical path.

The extra circuitry on top of the power PCB is decoupling and smoothing for my external power supply to the camera. This could be put underneath the board into what was the battery compartment.

[Gina]

Been thinking more about this. Can't really progress it until I'm confident with the debayering but no harm in planning

Been working out how I might use this camera when converted to mono. It would be useful for widefield use in particular - much wider than I'm doing with the 3 lenses and Atik mono cameras. Unless I were to debayer three DSLRs (or 4 even) I will need to change filters so a filter wheel would be beneficial as I said above. A mono camera is useful for NB and Luminance with an OSC for the colour of stars. So I thinking of Ha, OIII, SII and Luminance filters. ie. a 4 position filter wheel. To go to RGB would be 3 more ie. 7 and whilst LRGB would be better than L + OSC I'm not sure it would be so much better particularly as I could use a dual imaging system with one mono and one OSC camera.

[Gina]

I think this could be one way of making use of cameras that are less sensitive than astro CCDs whilst making real use of their large sensors. With SLR lenses working at f4 that were designed to cover twice the area there will be plenty of light and a flat field.

[Gina]

Now to the debayering...

Sensor number 1.

Part 1. Removing the cover glass

This was achieved with a craft type hot air gun and a home made extra nozzle made from thin copper sheet as used for the cold fingeres. The hot air gun :- http://www.amazon.co...0?ie=UTF8&psc=1 and these photos show the mini nizzle and fitting.

Heating the edge of the cover glass to break the bond.

The nozzle was held 2-3mm from the surface near to edge of the cover glass and slowly moved arounfd the edge of the glass taking 10-15 seconds to go all the way round and not pausing in one place. After going round once everything was allowed to cool down. This was repeated until the glass bond was seen to be breaking by colour fringes appearing between glass and frame. Firstly, a short section of bond appeared loosened then the rest of the bonded area was heated as before - equally slowly and carefully. After a couple of goes the bond was loosened all round. Next a double sided adhesive pad was stuck onto the glass covering most of the area so that if the glass did break pieces wouldn't fall onto the micro fine gold wires. Then a needle was used to remove a bit of the glue all round the glass taking care to use only slight pressure so as not to break the glass. Finally, the tip of a craft knife was slowly and carefully run around the edge to prize off the glass by about a hairs breadth until the glass was clear all round and could be lifted off. I succeeded in removing the cover glass in one piece

[Gina]

Part 2. Applying epoxy resin

Epoxy resin was applied to cover the fine gold wires and their connections to prevent inadvertent breakage when removing the CFA. It took two aplications to cover the wires and their connections to the actual sensor.

[Gina]

Back to cooling for the moment...

I've been looking at how to reduce the sealed and desiccated part to the minimum and thinking I may be able to move the battery box outside and even maybe the main board. Apparently plastics are not completely moisture tight and molecules of water can penetrate through. BUT I would have thought this was extremely slow and if desiccant were to be put in the sealed enclosure that this would absorb these water molecules such that the humidity could be kept sufficiently low. So I'm proposing to use plastics where metal would be impractical.

I think I may even be able to have the imaging assembly outside the sealed area.

[Gina]

Because the cooling part of this could get rather long I've decided to separate the debayering from the cooling and mechanical redseign. Also the debayering I started writing up here went wrong and I ended up with a dead sensor.

The Debayering will continue in the "Debayering an 1100D sensor (Removing Colour Filter Array)" thread - http://stargazerslounge.com/topic/194781-debayering-an-1100d-sensor-removing-colour-filter-array/

[Gina]

Since this thread is describing an unsuccessful debayering attempt and little else I have decided to start a new thread for the cooling side as well :- http://stargazerslounge.com/topic/194781-debayering-an-1100d-sensor-removing-colour-filter-array/

So this thread has now been replaced with two separate threads and will have no more postes from me.

[AstroShomy]

Could you please check the last link, I don't think it is related to the cooling part.

[Gina]

Ooops you're right - the link should be :- http://stargazerslou...100d-mono-dslr/

Sorry about that and thank you for pointing it out.