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Heated All Sky Camera Dome - ASI120MM Camera


ArmyAirForce

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Back in August, I started experimenting with my ASI120MM all sky lens. Living in a Bortle 8~9 light pollution area, I didn't know how well the small lens would pick up stars amongst the general sky glow and local light sources. Initial tests, with the camera mounted on a tripod at various places in the garden were promising, shooting 15 second exposures. The first picture is a combination of several pictures, also catching a satellite trail as well as a meteor ( hence the star trails ).

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This picture wasn't bad either, even with bright Moon rising.

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After the initial tests showed promise, I decided to make a housing so the camera could be left out recording all night, and be protected if it started to rain. I found a clear dome on Ebay and set about making a removable housing to attach onto the observatory. I wanted it removable so the clear dome wasn't exposed to UV and all weather. A wooden box was made to attach the clear dome onto, and it was covered in cotton fabric attached with dilute waterproof PVA glue. After it was cured, it was given a coat of the same grey exterior gloss as on the observatory roof. All went well with the construction and I looked forwards to testing it.

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The camera housing was designed with a single bolt to attach it to the observatory, and two locating pegs to set it horizontally. The initial tests inside the dome showed up a couple of problems. Its position on the side of the observatory was chosen to use the playhouse roof to shield the camera from a nearby street light. This worked to some degree, but stray light reflecting off the house, and neighbours bedroom/bathroom lights turning on and off, reflected off the clear dome, causing reflections spoiling the capture. A quick test solution was to cut a section of 6 inch postal tube to drop down over the clear dome. This reduced the field of view a little, but blocked stray light shining directly onto the dome. In the picture below right, the raggy edge of the top of the tube can be seen illuminated by the local light pollution.

The second problem was that after an hour or so, the dome started to fog and dew up, cutting visibility of the sky - also seen in the two pictures immediately below. OK, so I was making progress, but further development needed!

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However, while the dome was clear, I got some great captures of the sky.

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By studying the constellations and comparing them to Stellarium, I was able to plot the field of view of the camera, orientation and also plot an Azimuth/Altitude grid.

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So!..... I needed some dew heating of the dome. But how to do it? Ni-Chrome wire or resistors inside the dome and a power supply? No, I didn't want to have to provide another power supply. Where could I find some heat for the dome? The camera wasn't providing enough on its own. As the cogs whirled around in my brain to think of a solution, the sound of my computer CPU fan was whirring away in the background.

Light bulb moment! The waste heat from my laptop CPU could be ducted into the dome.

I set to making the modifications. This involved cutting some warm air slots around the camera to allow the air into the dome. The observatory laptop is mounted in an aluminium carry case. The next modification was a wooden box behind the CPU outlet to direct the warm air into a flexi-hose. The other end of the hose was fitted into the camera box, and camera sensor and dome temperature testing was done on the patio. The tests showed promise, so I was then prepared to cut holes in the observatory for the warm air hose.

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A new plastic light shield was cut to keep out stray light. A hole was cut and a piece of pipe glued in to link the flexi-hose to the removable camera box. A plastic cover keeps bugs out when the camera is not fitted. Inside the observatory roof, the flexi-hose plugs onto the tube glued into the roof, and the other end into the laptop outlet.

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Last night, after 11pm, the sky cleared, so out I went to set up a proper all night test.

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It was all plumbed in and the captures were set away, and after an hour or so of monitoring, I locked up and went to bed.

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This morning, I went out to check on things, and found the observatory roof covered in dew, but the dome was still clear!

While there weren't a huge number of interesting targets last night ( no meteor shower! ), I caught a meteor, satellite, some airliners and helicopters, plus got a nice time lapse of 6 hours and 38 minutes of sky.

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Here's the video. Over 6 hours in about 1 minute.

 

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Interesting solution :D  And a good result :) I used heater resistors in mine but I already had power as I use a Raspberry Pi 3 and Wi-Fi connection for imaging.

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The laptop exhaust solution is genius!!! I often think how much energy is wasted into thin air when I touch my MacBook, especially since I have the AC running all day!!!!

If you are running Windows and are thinking of having the camera on permanently you might be interested in some software I've written for that purpose. It's still in 'beta' version but there are quite a few observatories round the globe who are using it and it works pretty well. If you are interested and would like to try it you can join this Yahoo group: https://groups.yahoo.com/neo/groups/allskeye-ascom/

Best of all - it's free :icon_biggrin:

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On 16/10/2017 at 11:13, AngryDonkey said:

The laptop exhaust solution is genius!!! I often think how much energy is wasted into thin air when I touch my MacBook, especially since I have the AC running all day!!!!

If you are running Windows and are thinking of having the camera on permanently you might be interested in some software I've written for that purpose. It's still in 'beta' version but there are quite a few observatories round the globe who are using it and it works pretty well. If you are interested and would like to try it you can join this Yahoo group: https://groups.yahoo.com/neo/groups/allskeye-ascom/

Best of all - it's free :icon_biggrin:

Link does not work... :)

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I put together a star trail image from the Saturday night data too. 4 hours 58 minutes and 45 seconds. The whole night's capture was longer, but clouds started coming over at the 5 hour mark, so I stopped the trail compilation at that point.

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