2010-10-15 - Camera Mount for Night Sky Photography

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2010-10-15 - Camera Mount for Night Sky Photography

The camera mount sits on top of a tripod. It has two horizontal base plates that are joined by a pivot and two adjustment screws for X-Y adjustment of the alignment towards the North Star. On top of the upper base plate there is a board mounted at an angle approximately corresponding to the angle towars the North Star at my location on the globe. The board is connected to another board via a hinge that one aligns towards the North Star using the adjustment screws. A scope aligned with the hinge helps improving the precision. A stepper motor controlled by the electronics in the box on the tripod leg turns a screw that pushes the upper board in such a way that it rotates to cancel the rotation of the Earth. The camera is mounted on a ball head on the upper board and can be aimed at any part of the sky for long time exposures without the stellar objects looking like arcs.	The electronics is powered by 12 V, e.g. from a car battery.	When making long exposures (several minutes), the camera has to be put in bulb mode and a remote release cord that can be locked in the shutter release state has to be used. Typically, cameras cannot be set to longer exposures than 30 seconds unless bulb mode is used. (The remote release cord is not shown in any of these pictures.)
One good way to make sure the lens is focused on infinity is to use the auto focus and aim at the brightest object in the sky which may e.g. be Venus. Then the camera should be put in manual focus mode and neither the focus nor the zoom (if present) ring should be touched. On many modern autofocus lenses, especially zoom lenses, the distance scale on the focus ring cannot be trusted.	The scope, the hinge (right under the scope) and the adjustment screws are clearly visible in this photo.	There are a number of LEDs mounted on the various parts of the camera mount to provide some light when operating it in the darkness of the night.
	The back of the stepper motor can be seen to the left.	The stepper motor.

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