All Sky Camera Revisited

[Gina]

The sensor temperature has now reached 22.5°C in the warm sunshine with the cooling on LOW so a bit more cooling would seem sensible.

[Gina]

With the high ambient temperature and strong sunshine I have the camera cooling on FULL and the sensor temperature is still 4.6°C.  Of course I can only cool the water to around 30°C or so - a little above ambient and it may well be above 30°C in the observatory.  Getting over 25°C delta T isn't bad for a single stage Peltier TEC cooling system.

[DaveL59]

still pretty fair Gina. Wonder if adding some freezer packs into the water reservoir would help, tho they won't last long in this heat of course.

[Gina]

In fact that's a perfectly adequate operating temperature but I'm glad I have an efficient cooling system - it was worth it in the end.  Tap water is nice and cold but no tap in the obsy 🤣.  The overflow water from the spring runs quite near the obsy and that is cold so I could pump that in but we don't get that many hot days in the year so not worth the trouble!!

[Gina]

Camera temperature has dropped to 3.3°C now as the clouds roll in.

[Gina]

Interesting clouds.

[Gina]

After several hours of rain I think I can say that the ASC is watertight.  The pressure equalisation and drain pipe goes into a small jar in the observatory containing a couple of 10g colour changing desiccant (silica gel) grains.  These have darkened a bit but still orange and there's no water in the jar.  With the desiccant open to the atmosphere through a small hole in the jar top I expect to see a gradual absorption of moisture from the air.  Air will be going in and out as the air in the ASC dome cools and warms.

[Gina]

Here are some images from the ASC showing cloud and raindrops on the dome.

Heavy cloud coming in before the rain.

Light rain just started.

Moderate to heavy rain.

Rain stopped and sunshine but still raindrops on dome.

Raindrops gradually drying off.

Raindrops now almost gone.

Edited June 27, 2020 by Gina

[Gina]

.

Edited June 27, 2020 by Gina

[Chriske]

Woow, nice one..!
A few days back we had a halo around the sun, was very nice.

[Gina]

Lovely.

[Gina]

Swapped the 2 10g silica gel packs for fresh ones.  The beads weren't green but were quite a dark orange.  Now refreshing in the microwave for a few minutes.  That was a week with lots of wet weather so that's not bad.

Edited June 28, 2020 by Gina

[Gina]

Still working fine.

Edited July 10, 2020 by Gina

[Gina]

[Chriske]

Gina,

What I'd do with all these pictures : making a time-laps covering a year long movements of the stars. Not a minute long or so, but stretched over 10 minutes or so, even longer.

[CedricTheBrave]

Looks good Gina

Mine has been running for a while now and I have noticed the dome, camera etc have all been affected by sunlight. The dome showing signs of fracturing and changing colour! Not sure it will last a full summer. It wasn't a cheapo one either. 

 

[Chriske]

It would be better to cover the dome when not in use, especially during daylight.
Sunlight(UV) will destroy all plastics in the end.

[Gina]

I guess it would be possible to arrange a motorised cover for the dome.  I did think of it at one stage but decided it wasn't worth it.  I'll see how it goes and if I find the dome is affected by next summer I'll look at a cover.

[Chriske]

I wonder btw how hot does the interior of the dome gets during the day when the sun is high in the sky.
As a matter of fact you created a greenhouse, be it small, but I think it's getting rather hot in there.
On top of it(pun intended) that dome is a big lens. What does it do with the real lens inside...?

Didn’t read the thread from the start, so maybe it has been discussed earlier, so sorry...

[Gina]

The dome is very thin clear acrylic and has very little focussing effect - it only very slightly changes the focus.  Commercial units don't have anything to stop the greenhouse effect on hot summer days.  Of course, I know mine doesn't need to be built down to the standard of commercial units.  At least it's now waterproof and works pretty well.  As I said I may look into adding a cover later.  There are other benefits of a cover apart from keeping the sun off - such as insect and bird droppings and general "muck".  It would have to be remote controlled.  OK not beyond my capabilities probably but a lot of work.

Edited July 13, 2020 by Gina

[Gina]

After several months use and working well, the ASC finally succumbed to ingress of wet following many days of torrential rain and gales so it's come indoors for a service.  There was mist in the lens which has now dried out and the camera is working and giving a reasonable image.  Except that the focus has changed! 

The reason for the weatherproofing failure was the silicone sealant.  We have had very large changes in temperature which could have been detrimental to the sealant.  Then a very high wind with heavy rain must have forced wet up the 20mm dome overlap and into the insides.  We are accustomed to horizontal rain but in this case the wet was forced upwards!!  Whether there's any way of preventing wind blown rain going up into the dome if the sealant fails, I don't know but I guess more thought is required.

Another problem is that over the months, the focus has changed slightly but enough to make me try refocussing.  Been trying to refocus the ASC but had forgotten how extremely coarse the focussing was.  Unlocked the focussing ring on the lens and moved it a "midgets whisker" and the focus was 10 times worse!!  I was hoping that the focus would remain pretty good once set up but it does seem to have changed.  Drat!!  Looks like it may need remote focussing after all.  I'll have to think about it.

I wonder if I'll ever get an ASC that continues to work as I want!!

Edited September 1, 2020 by Gina
typos

[pete_l]

1 hour ago, Gina said:

the ASC finally succumbed to ingress of wet following many days of torrential rain

Last night I was running a Pi with its 8MPix IMX219 camera. See the photo enclosed

After bringing it indoors to tweak the focus, the very next images had these white splodges on them. I immediately thought that the lens had got some smudges on it. It never occurred to me that they were clouds

P.S. With a 10s exposure at full resolution the camera sees down to Mag 5 - maybe 5½. When the Moon goes away I'll see if it goes any deeper. This is for a meteor detection system.

 

P.P.S To fix your water ingress problem, have you tried a rubber sealing gasket rather than silicone sealant.?

Edited September 1, 2020 by pete_l

[Gina]

Yes, I have but may try again.

[DaveL59]

hi Gina, you may find that if the sealant shrank a little capillary action would draw water in even through any hairline cracks without the wind driving it. I think that's partly what happened with the smaller of my two when it got water, tho the dome/metal ring arrangement won't have helped on that one either. The other with a neoprene washer under it so far seems untroubled.

I guess thermal creep may be what's affected the focus? I've had to tweak a couple of the regular CCTV cameras over the 4 years here, very slight but a nuisance as you only see they've drifted at night when they switch to IR night vision so then end up fiddling in the about with them dark. Day/colour seems fine with focus a touch out as there seems to be just a slight difference between Day/IR-night, perhaps the effect of switching from IRCut to clear filters, tho a couple of them are colour only (no cut filter) and see the same effect under IR lighting..

Edited September 1, 2020 by DaveL59

[Gina]

I'm looking again at the clamping and sealing of the dome.  I would like a dome with a wide flange with holes for screwing the dome down but these are still still out of stock (as they were before).

These are the two domes - I have the one with the narrow flange.  I have tried many makes of dome in the past but these are the only ones that are distortion free that I have found.  I could print a ring with fixing holes that would emulate a flange for clamping down the dome.  It should be possible to get a seal using some EPDM sheet left over from my obsy roof.