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 Post subject: One definition of stress
PostPosted: Sun Mar 04, 2012 4:49 pm 
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Hi folks,

Apropos my Green Arkleseizure post elsewhere:

Stress is turning on a new power supply in the knowledge that, however many times you've checked your wiring, an error could fry over $15,000 worth of camera and telescope mounting. :shock:

So far so good. Maximum current draw (at 12V), almost entirely by the camera as it cooled down to -25°C, was 4 amps which gives me a 20% margin below the maximum specification for the mounting's power distribution outlet and obviously my plug/socket/switch wiring was good. I'll relax a bit more after a few night's observing and testing of the second unit is complete as well (two units - one for camera plus Pentax lens and the other for camera plus telescope) but for now "Phew!"

I think I'll take the rest of the day off and have a nice cup of tea and a buttered scone or two as a reward. :)

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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PostPosted: Sun Mar 04, 2012 5:15 pm 
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I was wondering what you were building. I assume the cooling devices (peltiers?) are a bit power hungry?

Sounds like you might need something a little stronger than tea!

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PostPosted: Sun Mar 04, 2012 6:16 pm 
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Hi popo,

Yep, it's the Peltier cooler that takes the vast bulk. Next in line is the Kendrick dew heater.

The point of the exercise was to use the 12V power already supplied to the mounting and get rid of the three mains power bricks. 240V is all very well but the less of it the better on dewy nights. I need to power the computer and lab power supply from the mains but I'll be very happy without those bricks, not to mention the cable clutter.

You are right - tea was refreshing but I'll enjoy a glass of red wine and a slab of Ameglian Major cow later on. :twisted:

Bob.

_________________
Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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PostPosted: Mon Mar 12, 2012 12:56 am 
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Hi folks,

Another definition of stress is trying to recalibrate a telescope mounting only to have the computer running the mounting, the camera, the filter wheel and the focuser freeze on me several times just at critical moments this evening. Turned out that with a single USB 2 cable managing all that data trying to download focus and test images in high speed mode (8MHz) was just a bit too much for it. Downloading those test images at 1MHz (something I always do for regular images) solved that issue.

Anyway, to cut a long story short, tonight was my first session with the astro CCD camera (ML16803) attached to the new telescope. The mounting was polar aligned and then trained using my old Televue Pronto 'scope entirely visually using a crosshair reticule eyepiece so slapping a new telescope on it meant at the least that, with the two telescopes not being exactly aligned in the same direction relative to the dovetail plate which attaches to the mounting, when I commanded the 'scope to point at Capella it missed by quite a large margin. Eyeballs to the rescue until I could get Capella into the field of view of the camera and then, joy of joys, I asked MaximDL to autofocus for me. Actually it wasn't that joyful because just before perfect focus was achieved the 'pooter locked up - it was about that time I discovered the 8MHz issue. Fast forward and repeat and autofocus worked perfectly second time around. I then dashed off 5 x 200 second exposures of the Pleiades using my blue filter as a "first light" treat and then got back to work...

If the mounting is slewed to a set of stars (via TheSkyX in my case) and then the pointing is fine tuned the software running the mounting can work out how good the polar alignment is so that was my next job. By the time I'd used four stars to create the needed pointing file it was already getting so foggy that I couldn't actually see many stars at all but the camera punched through the haze and when I asked the software to display the polar alignment error I was delighted to find it was only 1.5 minutes of arc out. The software also very usefully offsets the pointing position by the error if you point the scope at a star near the meridian which allows the adjustment screws on the mounting's base to be tweaked until the star is back in the center of the crosshairs of the image (crosshairs courtesy of MaximDL) so I'm now polar aligned to comfortably less than one minute of arc.

Actually, as it turned out, I needn't have bothered because the mounting's documentation suggests that 10 minutes of arc is usually good enough and 3 minutes of arc is certainly good enough. That's because the mounting is subsequently trained with a much larger selection of stars (30 or so) in all sections of the sky and as a result not only compensates for small polar alignment errors but other errors such as flexure and atmospheric refraction. No time for that tonight but I'm chuffed to bits over the polar alignment result as it imples that the telescope pier I built last summer has remained rock solid. So maybe I'm not feeling stressed after all. :)

Oh, I'll process those first light images after a good sleep and share them in an appropriate thread. 8)

Bob.

_________________
Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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