All Sky Camera Revisited

[Gina]

Redesigned the outer casing to attach to the ROR.

[Gina]

Focus Motor with pinion added.

[Jonk]

I'm curious as to why a focuser is needed? Mine doesn't appear to shift at all, between a hot sunny day and cool night it appears to be fine.

Maybe smaller pixels help there?

[Gina]

The dome changes the focus slightly so focus needs setting with the dome on.  I manage to get reasonably good focus by using a distant range of hills but the stars are still the best.  I'm using a camera with 2.4µm pixel size in a 1/1.8 inch sensor (5mm vertical) giving a resolution of about 2000 pixels in each direction of the round image.  I guess I'm rather fussy about focus.  I may decide to try preset focussing and only add the remote focussing if I find I need it.  As long as I allow for it in the design, I can add it later.

[Jonk]

Interesting..... are you sure that the dome's refraction cannot be corrected by changing the focus on the camera?

At first guess I would imagine it won't.

I would focus the camera then fit the dome.

I found using the moon worked best as stars are too small!

[Gina]

In previous versions I have found that with the camera focused without the dome, the focus was a bit out with the dome on.  This could be corrected with the remote focussing.  It should be possible to find out how much and in which direction the dome changes the focus and make a correction but how can you do that without access to the focus ring on the camera (covered by dome)?

[Jonk]

If that works, great... how to do it? I suppose I would focus on the moon without the dome, place the dome and see the change on screen immediately, remove the dome, adjust, then replace.

Repeat until happy then screw the dome down?

I fitted an o ring between the lens and camera so a small adjustment wither way would not end up with a loose lens.

[Gina]

Yes, that is certainly one way to do it.  The moon (if available) is certainly a good object to focus on.

I would assume you are using the Fujinon lens and it's screw thread for focussing.  Have to say, I found that very coarse and rather difficult to cope with.  The lens I'm using now has its own focussing ring which is silky smooth and not loose.

[Gina]

New RS Peltier TEC has arrived and I've set it up to cool the camera using the 80mm fan and Artic passive cooler as before.

1. Time 14:15 - Starting temperature 27.5°C - TEC supply 13.8v and drawing 3A.
2. Time 14:20  - Temperature 7.5°C - TEC supply drawing 2.8A.
3. Time 14:25 - Temperature 6.5°C - TEC supply drawing 2.8A.

Seems to have settled after just 10m.  That's a drop of 21°C.  Temperature has come down fast!  What a difference from the cheapo TEC1 12703!!

Edited October 14, 2019 by Gina

[Gina]

Temperature has come down another half degree and 20m in.  Ambient temperature is 19.5°C.  So running the camera with no cooling raises the temperature by 8°C and the cooling decreases the camera temperature by 21°C in the present test conditions.

Oooops!!  Just noticed I didn't have the camera thermal jacket on - camera covered in condensation!!

[Gina]

Put the camera cover on and it's getting colder - now down to 2°C.

Edited October 14, 2019 by Gina

[Gina]

Dropped below freezing now and at -1.5°C.  Still slowly getting colder.

[Gina]

Camera is still working fine at -3°C and still slowly getting colder.  The condensation doesn't seem to be affecting it.

[Jonk]

Makes a difference huh?!

Also the better the insulation and cooling, the better the efficiency and therefore lower cooling limit.

I found by setting the controller to -10, I got to -5 in the camera body, ccd sensor was reporting 1 I think with it on 10fps. This was indoors at a desk, with ccd starting temp at 30 after running a while, and ambient of 21 or something.

I think I'm happy with that.

With 60 second exposures, the temperature will drop slightly and rise on the sensor read cycle but that's to be expected.

There must be a lower limit you're prepared to go? Not just diminishing returns but also ice on the inside of the camera body condensing onto the electronics when you stop cooling or the cooler is in fault?

[Gina]

[CedricTheBrave]

that looks good to me

 

[Gina]

2 minutes ago, Jonk said:

Makes a difference huh?!

Also the better the insulation and cooling, the better the efficiency and therefore lower cooling limit.

I found by setting the controller to -10, I got to -5 in the camera body, ccd sensor was reporting 1 I think with it on 10fps. This was indoors at a desk, with ccd starting temp at 30 after running a while, and ambient of 21 or something.

I think I'm happy with that.

With 60 second exposures, the temperature will drop slightly and rise on the sensor read cycle but that's to be expected.

There must be a lower limit you're prepared to go? Not just diminishing returns but also ice on the inside of the camera body condensing onto the electronics when you stop cooling or the cooler is in fault?

I've gone down to -20°C in the past with water cooling on the TEC hot side but with sealed camera chamber and desiccant.  I'm planning the same dry environment for the camera in this latest version.  At least damp condenses on the case rather than the electronics but I still don't want to risk it.

[Gina]

The camera casing was wet when I touched it so better thermal insulation is possible.  The plan is to have a moisture barrier around the camera and Peltier TEC including the USB plug with a small amount of room for desiccant.  Outside that would be thermal insulation - there's plenty of room for that.  I have plenty of closed cell polyurethane foam.  I also have kitchen foil (shiny aluminium foil) if that would help.

[Gina]

I did a test for focus shift from the dome using the ceiling light fitting to focus on.  The difference seemed to be about 10° clockwise rotation of the focus ring from no dome to dome but I shall do a more accurate measurement on the moon if/when we get some clear night sky.  There's rain forecast for all night tonight.  I reckon there's a reasonable chance of using preset focus, avoiding focus motor and gears etc.

[Gina]

I've been looking into various ways of sealing the camera to keep damp out so that I can cool it well below freezing and also maybe include some desiccant to dry any air already inside.  The cooling tests have shown that even without sealing and desiccating, no wet gets onto the circuit board or upper part of the inside of the casing.  All the damp/wet is in the bottom away from the electronics.  I guess this is because the bottom is colder than the rest and any condensation prefers the colder parts.  This makes me wonder if I'm over-thinking the situation.

[CedricTheBrave]

Gina

how many and what rating are the anti dew resistors and how are you powering/controlling them?

 

[Gina]

Haven't decided yet but previously I have used 6 x 6Ω which is 36Ω giving 5.3W from 13.8V or 0.7W from 5v.

[Gina]

Regarding camera thermal insulation, I thought I had closed cell polyether foam but it turns out to be open cell.  However, I have plenty of polystyrene foam blocks that I could carve up for camera insulation.  That is a very good thermal insulator.  But the easiest form of insulation would be 3D printed where I only have to design the shape in CAD software and print it.  This would be self-supporting and easily attached to other parts whereas polystyrene would need enclosing to hold it in place.  With 3D printing I can use honeycomb infill with solid layer every few layers to form closed cells.

The camera thermal insulation would almost fill the space in the outer casing below the lens leaving the air in the dome.  I'm thinking I might go back to my previous idea of drying the air in the whole ASC casing with silica gel bags and hermetically sealing the outer casing.  This would be easier if the RPi were also in the outer casing as then just two connections need pierce the sealed enclosure.  Heat from the RPi would aid dew heating that I think a dew heater would still be needed to stop dew on the outside of the dome.  Since this will be a nighttime only ASC, the RPi would not be powered in daytime and overheating would not be a problem.

[CedricTheBrave]

tested the new cam out on the patio steps on top of a plastic bucket!

the moon had a say in matters but quite please with first test out of the box.

[Gina]

Are you satisfied with your sky coverage?