All Sky Camera Revisited

[Gina]

Also planned for today :-

1. Re-route CAT6 cable to enter observatory through warm room - reduces outdoor part of cable run and allows for Ethernet switch in warm room.
2. Make hole in observatory wall behind the ROR window for cables and water pipes.
3. Take RPi plus bench PSU into observatory, connect camera USB and power up.
4. Go back indoors and fire up KStars/Ekos to test ASC camera operation.

 

[Gina]

Done that too except that the hole on the observatory wall is not yet big enough for the water pipes.  I wanted to test the location ASAP and IT WORKS though it looks like the focus might have been knocked a bit - doesn't look as sharp as it was.  Maybe I should resurrect remote focussing - groan.  It would need a much bigger enclosure to accommodate a stepper motor.  Anyway, time for a cuppa...

Here's a screenshot of the KStars FITS Viewer image, cropped to remove most of the black.

[Gina]

Had a thought - camera is in almost full sunshine and temperature is over 36°C so thermal expansion may well be the cause.  ATM I have no cooling of any sort.  Once I have the water cooling connected up I can cool the camera but don't know about the lens, it's connected to the camera so may get cooled.  Guess I'll see what it's like once I get the water cooling working.   Probably the next job after I've had a rest.

[Gina]

Camera temperature has risen to 48°C now!  Definitely need daytime cooling as well as at night.

Edited March 25, 2019 by Gina

[Gina]

Water cooling installed (temporarily) and Peltier TEC connected to 9v.  Camera temperature is falling.  Focus doesn't seen to have changed though so probably needs resetting but I'll see what the stars are like as it might be just the edge that's out of focus due to the dome.  I'm hoping to get good focus all over but no point in changing the focus before testing at night as changing focus means taking the ASC & mast down.

[Gina]

Camera temperature now -10°C (yes, minus ten).

Another image.  Still at minimum exposure of 32µs and gain at 0.  Mostly clear blue sky with a few contrails.

[Gina]

Camera temperature still going down and now -12°C.  The water cooling is very efficient at taking the heat away from the Peltier TEC.

[Gina]

Camera temperature -14°C, everything else the same.

[Gina]

Camera temperature -16°C, everything else the same.

[Gina]

Here's a photo of the ASC installed on the observatory.  It's turned out a bit higher than I intended but it doesn't matter.  The water pump can easily raise water to the required height and thoroughly flush the waterblock. 

I might possibly put the wind instruments for my weather station on the same mast just below the ASC.  OK so accurate results require a mast some 5m above surrounding wind obstructions but I'm not really bothered about getting an accurate wind speed and direction - a rough idea is good enough.  Better than I have ATM ?

Edited March 25, 2019 by Gina

[Gina]

Another photo, this time from the east window of my living room at full zoom.  The orange showing inside the casing is colour changing silica gel desiccant - turns green when exhausted.

Edited March 25, 2019 by Gina

[Gina]

Another image.  Camera temperature -19°C, everything else the same.  Still waiting for sunset (18:33) ?

Edited March 25, 2019 by Gina

[Gina]

Sunset has occurred.  New image - 3ms exposure, gain 0, camera temperature -22.5°C.   I think there might be some dew on the dome - I might go out and apply power to the dew heater.

[Gina]

The dew heater doesn't want more than 6v so for the time being I've reduced the bench PSU running the water pump and Peltier TEC to 6v and connected the dew heater.  The other bench supply running the RPi at 5v doesn't have the current capacity.  This has reduced the camera cooling which is now at -12°C but the dew has gone and trees are again visible on the horizon.

Edited March 25, 2019 by Gina

[Gina]

20s exposures now and camera temperature at -10°C which is still keeping the noise st bay.  Just waiting for it to get dark enough for stars to show then I can see what the focus is like.  Edge of view is certainly out of focus and I'm betting the centre is too.

[Gina]

I was right - stars out of focus.  Here is a 60s image still with gain set at 0 and camera temperature at -11°C.

[happy-kat]

Can you adjust focus without bringing it down from the pole?

[Gina]

60s image with gain set to 200.  Camera temperature about -10°C.

[Gina]

5 minutes ago, happy-kat said:

Can you adjust focus without bringing it down from the pole?

Not really.  I guess I could use the step ladder against the side of the observatory and remove the dome to get to the lens to focus it but I wouldn't know which way to turn it or by how much - I would need a monitor up on the observatory roof to see when I had focus.  It was the difficulty of manual focussing that led me to add remote focussing to earlier versions - I just wondered if I could manage without it this time.  The only way to manually focus during daytime is to have the ASC pointing to a distant object ie. horizontal rather than vertical.  Personal safety tells me not to try clambering up onto the observatory roof at night and fiddling with the ASC.

I could take the ASC & pole down during daylight, refocus on the horizon and put it back up.  The dome didn't seem to make much difference when I tested it on and off but I'm sure it must.  I guess the only real answer is to return to remote focussing, otherwise I'm just going to be wasting clear night skies trying to get the focus right manually.  Professional ASCs don't have remote focussing but I guess they have all the equipment necessary to preset the focus accurately - I don't!

[happy-kat]

That's unfortunate that  focus is slightly out, I'm sure you'll sort it in daylight.

[Gina]

That's not just slightly out - it's miles out.  I'll take it down tomorrow and try refocussing or at least check that the focus looks that much out in daylight.

Fortunately, making a new casing to accommodate one of the small stepper motors is just a matter of redesigning it and printing a new version.  I think it will need the 4" dome though as the 3" one is already a tight fit.

Edited March 25, 2019 by Gina

[Gina]

It's dark now so I've captured another image - 60s with gain of 200.  Camera temp -11°C. 

[Gina]

Even though the focus is way out, this has not been a totally wasted night's imaging. 

1. I have shown that the coverage of the sky is fine - there is a thin ring of ground round the whole circumference of the image.  There is no point in covering any more as an all sky camera.
2. I have also shown that the camera cooling system is well able to kill any hot pixels and remove noise - it has performed well beyond expectation.  This last image is showing some noise in the image but the signal to noise ratio is adequate even with the cooling running at half power.  Getting the focus right will increase the signal from the stars considerably. 
3. Dew heating is necessary to prevent the formation of dew on the outside of the dome.  I shall probably alter the dew heater to run off the full 13.8v of my observatory power supply.

[JamesF]

Looks as though you might need to rotate the camera about 15 degrees if you want to have north at the top?  Some nice star colours there though.

James

[Gina]

It's certainly a bit off but maybe not quite as much as 15°.

Edited March 25, 2019 by Gina