Gina

Print finished.  Here are a couple of photos with the top camera casing, camera, lens and focus motor added.  Rather a rough print at high speed just as a prototype - not the finished version.

Thought I'd  do a Google search for aluminium boxes with the thought that a Peltier TEC in the bottom could warm the dome and found another possibility :-
ALUMINIUM SQUARE BOX SECTION 11 Sizes 10 Lengths  with one option as 4" square and 100mm high.  That's 4" outside and 3mm thickness.  This makes the inside 95.6mm square.  Now the passive cooler is 95.0mm square so the top of it would fit nicely inside the box section.  It would need clamping on and sealing to keep damp out but it's an interesting idea, I think.

The Peltier TEC eventually came off the passive cooler so I can change the cooling if I want to.  OTOH passive cooling does have its advantages.

It's just occurred to me that I was going to use some of the heat from the hot side of the Peltier TEC to warm the underside of the dome to help with dew heating and stop dew on the outside, but now I don't see how I can.  It just seems daft to have heat to get rid of and heat wanted under the dome yet "ne'er the twain shall meet".  I may get thinking again and see if there is any way of using the spare heat.

Next try at the model for the bottom casing.

Not right yet but going in the right direction...  Needs more room for the focus motor.

Here's a screenshot of the first CAD model.  I think I'll print one and see how it goes.  There are other bits to add such as clamping for the camera casing top and attachments for the top part of the outside casing.

I think combining the two is on.  There would be a 5mm gap between the housing and the cooler which could be filled with rubber foam for sealing.  The disadvantage would be that this seal would by the only thing separating the camera from the atmosphere unless I use sealant around the Peltier TEC and its leads.

I'm just wondering if the bottom of the camera casing and the bottom of the outer casing want printing in one piece.  OTOH I doubt this would be possible without support material.

Gap between camera casing and and passive cooler is just 4mm.  From cooler to top of camera housing is 44mm.

I think the outer casing is going to have to be in two parts bolted together.

The camera clamping could be part of the outer casing.  This would mean the outer casing could be attached to the passive cooler with the four threaded holes in the cooler and M3 screws.  Rubber foam could be used as the seal between casing and cooler.

Still to do :-

1. Pair of gears for focussing.  Simple.
2. Clamping camera to Peltier TEC.  Not so simple.
3. Outer case design with weather seal.  Difficult.
4. Fixing to observatory.  Relatively simple I think.

The observatory jobs are on hold today - weather not good enough for roof repairs and waiting for parts for the roof automation - so this project may get some attention today, if I can get my brain to engage! ?

Here's a screenshot of the FITS image - out of focus!  30s and gain at 50.  Camera temperature 1.2°C no cooling.  Too tired tonight to do much but may do more to it tomorrow though whilst the weather is good I want to do the observatory.

This needs work before I can do any more testing.  The focus I set up manually needs setting up again and it's very critical - a few degrees rotation makes a difference, so I need the motor focuser working.  I also need to arrange to clamp the camera onto the Peltier TEC.  Then there's the outer casing and dome to sort out, with the problem of sealing.  I've been concentrating on my observatory today.

I guess I could cover the whole dome and take a dark.

This ASI 120MC-S camera seems to be more sensitive than the ASI 185MC though I guess it's difficult to tell with the moon in the image.  There another difference too - when the 185 was imaging the sensor temperature increased whereas with this one it doesn't.  The 185 had a separate image sensor PCB whereas this has the sensor mounted directly on the main PCB.

I guess I should stop imaging and get on with the construction...

Camera temperature has now dropped to -0.2°C.  Part of image - 60s exposure, gain of 50.  The clouds have gone.

Camera temperature has now dropped to 0.5°C.  Part of image - 60s exposure, gain of 50.  Here comes the cloud...

Camera temperature has now dropped below 1°C.  Part of image - 30s exposure, gain of 50.

Camera temperature has now dropped to just over 1°C.  Part of image - 30s exposure, gain of 50.

Camera temperature has dropped to just over 2°C.  Part of image - 10s exposure, gain of 50.

7 minutes ago, Stub Mandrel said:

Mine responds very well to darks for those hot pixels.

Darks are a problem as the lens doesn't have a shutter or aperture control.

Moved ASC outside onto the window sill.  It's now slowly cooling down towards outdoor ambient.  I realised that I'm not ready for cooling as the camera needs clamping onto the Peltier TEC.