Gina

When I was using the ASI 185MC camera with Fujinon f1.8 lens I used 60s exposures mostly but I don't know how the ASI 178MC compares with the ASI 185MC for sensitivity except that the 185 has bigger pixels, in fact the same size as the 120. I'm thinking 60s exposures may be more appropriate for 178MM darks.

Decided I'd take some darks at various temperatures with the ASI 178MM camera. A direct comparison is difficult as the pixels of the ASI 120MC-S are 2.4x those of the 178MM though the 120MC has the Bayer layer to reduce sensitivity. What I think can be said is that the 178MC should be affected in sensitivity much the same as the 120MC. I think dark noise would be the same for MC as MM given the same sensor otherwise. So I reckon 30-40s exposures will be wanted for the 178MC for nighttime images and hence I propose taking 30s darks with the 178MM.

Yes, I have used the Fujinon 1.4mm lens with the ASI 178MM and did get full coverage. When funds permit, I'm planning to buy an ASI 178MC camera.

These are the connectors I have in mind for the ASC - they seem to be sealed - I already have 4 pin and 2 pin types. Multi Contact Multi-Pin Connector Chassis Socket or Plug Microphone Aviation x1

Commercial ASCs do not have remote focus from what I can find and I think the focus should remain good once set up. If I can do away with remote focussing I can save 4 wires from the controller to the ASC. If I want to use the ASI 120MC-S and Fujinon zoom lens for daytime imaging it will need the aperture control. This can also be used to take darks as the aperture completely closes. The disadvantage is the need to include a servo motor within the ASC casing. Connections required assuming no remote focussing :- USB cable. Peltier TEC - 2 wires. Dew heater - 2 wires. Servo motor - 3 wires. No. of wires required is not 7 as some may be combined - a common ground for instance. The servo motor needs ground, +6v and signal, TEC & dew heater need the +12v line as the electronics is ATM but I could change it. If I keep the +12v line that makes 6 wires otherwise 5. I could use a 6 way round cable or a sealed plug and socket.

I think the next design decision is whether to put all the electronics in the ASC housing. The advantage of having it inside the ASC casing is that it reduces the number of wires going into the sealed ASC casing plus the heat generated can help with dew heating (that's dew on the outside of the dome - the air inside is desiccated). The disadvantage is that the ASC would want shielding from the summer sun to stop it overheating and also it would make the housing a lot bigger. Silicone sealant can be used for sealing the wires where they go through the casing so I don't think that would be a problem. Overall, I think I would prefer to have the temperature inside the ASC controllable rather than leaving it up to "the elements". I think that's another decision made ?

I shall concentrate on the "Economy" version for the moment - I've no idea of how long delivery of the big Fujinon fixed focus lens will take, only that they say it's been sent. OTOH most of the design ideas I'm working on will apply to both versions. From testing the ASI 120MC-S camera and darks I've concluded that the passive cooler is inadequate as the camera temperature needs to be well below freezing to reduce noise sufficiently and I shall be going for water cooling (not as complicated as it sounds - just think of the flexible tubing for the water as cable carrying water rather than electricity). Having decided on the cooling system, the next question is the mounting. Whilst there are advantages in mounting the ASC on the apex of the roof such as just needing to be screwed to the barge boards there are serious problems with where the water cooling reservoir is mounted. Also, with the rolling roof the power cable has to loop down, with a possibility of catching on something and is subject to flexing every time the roof is opened or closed. The alternative is a mast (1¾" OD aluminium tube - very stiff and strong) attached to the observatory main framework with a strong bracket to bring it out clear of the rolling roof. The bottom can go in the ground. I think the mast mounting wins.

I'm definitely going for water cooling for the ASC - the passive cooler is inadequate and feeding dry air to a fan is more awkward than water cooling. The waterblock is smaller than any sort of heatsink/fan arrangement. I'm now working on the design of the ASC parts.

Guess what??? I've fixed the seemingly duff pump. Having relaxed watching a bit of TV I decided to take the pump apart and see if I could see anything. I did, a couple of little bits of what looked like plastic in the impeller. Removed them, put the pump back together and resisting the temptation to test dry, I connected it to the reservoir and half filled the reservoir with water. Put the pipe from the pump into the reservoir and applied power - pump worked fine ?. Oh well I shall have a spare tomorrow! Connected the water tubes to the waterblock and mounted it high up. Applied power to the pump and it forced water through all the pipework and waterblock flushing out all the air. I believe this is going to work. From previous experience, water cooling is an extremely efficient method of getting rid of heat.

The term "steep learning curve" comes to mind!

I've tried that but no joy. I even tried with the waterblock below the reservoir. Tried tapping the pump, forcing water through it in the normal direction but nothing worked. I know these pumps can fail if there's no water in them when switched on but I haven't let that happen. I checked the spec of the pump i was using and it can pump water up 2m. The new one I've ordered can lift 3m. Actually, a couple of feet will be sufficient on the observatory. On re-reading your post, the bottom of the reservoir is at the same level as the pump with the reservoir having at least 5" depth of water. It's the waterblock (that cools the hot side of the Peltier TEC below the camera) that has to be higher than the reservoir. The pump never works with negative pressure.

I'm getting a bit fed up with the way things are going wrong these days. Whatever I touch seems to break!

Hmmppfff... the little water pump has gone wrong - about every 5s it draws 200mA for about a second and is not pumping! Had to order another but this time a slightly bigger one (5W rather than 3.6W).

While the new camera casing bottom part is printing I have set up the waterblock on top of my anglepoise lamp connected by silicon rubber tubing to pump and reservoir. There doesn't seem to be any problem with the waterblock a lot higher than the reservoir and pump - ATM a couple of feet but I'm hoping it will be alright with several times that.

Now to design some 3D printed parts for it...

I have round waterblocks with pipe connections on the back which I think will be easier to use in the ASC than the square one with connections on the side. The size is about the same as the camera. This photo shows camera and waterblock upside down. The tubing shown is rather small and I have ordered some larger size silicone rubber tubing (8mm bore 12mm OD x 5m).

When trying to attach the 3D printed base plate to the passive cooler I found a problem with the threaded holes. I thought they were M3 but they aren't. Not M4 either but something in between. Then it occurred to me that they might be Imperial, maybe 4BA with a size of 3.6mm. I used to have 4BA screws but don't know if I can find any now. I do have the original supplied screws so will probably use those and modify some of the design to suit. Or I might leave that for now and try some water cooling experiments.

I just have to modify the design of my present camera housing a bit to accommodate the Fujinon zoom lens and 3D print it. I can then provide a thermally insulated and sealed camera enclosure with the passive cooler. Last night I was using an 80mm fan to blow cooling air through the fins of the passive cooler as well as running the Peltier TEC at it's most efficient. This doesn't bode well for using the passive cooler without fan in the summer so water cooling is looking more relevant and I shall be doing some testing.

To go lower in temperature I shall have to make a proper rig. A casing for the camera to provide thermal insulation and desiccant to remove the moisture plus proper pressure to hold the camera body to TEC and TEC to cooler. There is still significant noise at 0°C so it will want the temperature taking down lower. That could prove difficult in a warm summer should we get one again.

Hmm... Can't get it any cooler on the table. I guess 20°C below ambient isn't too bad as I haven't got any thermal insulation round the camera so it's taking all the water of or the atmosphere.

I don't see why not.

15°C 10°C 2.7°C 0°C.

Currently taking a set of darks. 15, 10, 5, 2.7, 0 degrees C so far.

I'll set up the ASI 120MC-S with Peltier TEC and passive cooler and run the TEC off a bench PSU to control the cooling and take a series of darks at various temperatures. I'll use an exposure of 15s as this seems likely to be what I would use for nighttime images. I'll leave the gain at 50 as that was what I did the sky tests at.

ATM the passive cooler is looking best due to simplicity of use. Of course, this would work better if the air had an unobstructed path with the cooling face vertical but that is impossible unless I had a big block or angle of copper but the extra thermal resistance might negate the improvement due to orientation.