Saturday, August 18, 2012

Astrotrac, first light

I recently acquired a tracking device for my camera, specifically the Astrotrac TT320X-AG with Tele-Optic wedge. AG in the product code means that it has auto guiding port, but I don't (yet) have such appliances.

This is how it sits on my tripod; first the wedge is on the tripod, and on the wedge is the Astrotrac and on the on the Astrotrac is the ball head and on the ball head sits the camera or lens. The wedge is used to align the axis of rotation to the celestial pole, as the sky rotates around that point and the camera must follow the stars while they move to avoid streaking of the stars.

Astrotrac TT320X-AG ja wedge Astrotrac TT320X-AG

The tracking device is basically built around the 20cm long screw and a motor which runs the screw and rotates the upper aluminium arm. As the arm moves, so does the camera mounted atop. Motor is powered by 12 volt power source, which can be a battery pack, transformer if the mains are close or accumulator such as lead-acid battery. Personally I built the power source from latter, a cable with 5mm round plug was needed to connect the two. If using rechargeable AA batteries, one must use ten of them because their voltage is lower than regular batteries (1.5V versus 1.2V from rechargeables).

Astrotrac TT320X-AG Operating the device is quite straight-forward: after aligning the axis of rotation to celestial pole and and the camera to chosen subject, the play button is pressed in the control panel. The star-like symbol controls the brightness of the indicator LEDs and and the volume button the... volume of the beeps. There's also button to rewind the screw. Volume and brightness buttons also choose the tracking rate if pressed while starting the apparatus.

After two hours of tracking the system must be rewound to continue. Depending on the batteries, there's enough juice to power the device for several nights of photography.

Anyway, here's the first light from the device. Polar alignment wasn't perfect as I did it by eye rather than drift-align or even polar scope.

Tähtitaivasta ja valosaastetta venerannalta
(Two and half minute exposure, it's not the tracking accuracy that's the problem but the sensor heating up as you can see in the corners.)

Nights aren't yet dark enough to capture the Milky Way very well, but in a week or so the night should be dark enough. The faint green glow is from northern lights that were present earlier, even though it was invisible to the naked eye, long exposure captured the glow in the sky.

Illan ja syksyn ensimmäiset reposet

Linnunrata ja revontulten kajo pohjoistaivaalla

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