Ken Hough's Website
Astrophotography

Equatorial Mounts

Why Equatorial Mounts:

There are two main types of telescope mounts in use:

-- AltAz (short for Altitude Azimouth). ie mount is driven in the horizontal and vertical planes
-- Equatorial. ie the Deg axis is aligned with the celestial pole so that the RA axis can then exactly follow the rotation of the night sky.

FOR LONG EXPOSURE ASTROPHOTOGRAPHY, A MOTOR DRIVEN EQUATORIAL MOUNT IS ESSENCIAL !

Motor driven/computer controlled AltAz mounts can be made to accurately track a target which appears at the centre of the field of view, BUT the field of view will be seen to rotate about the centre of the field of view. Peripheral stars will appear as small arcs rather than as points of light. Field "de-rotators" can be used to elliminate this effect, but their use is not common in amateur work.

Many well known Schmidt Cassigrain and Maksutov telescopes are supplied with AltAz mounts. In this form, they are not suited to astrophography. With the addition of an EQUATORIAL WEDGE, these mounts can be tilted over to perform as equatorial mounts.

However, purpose made equatorial mounts can have advantages. Adjustable counterbalance weights are provided. This allows for precise setting of balance irrespective of weight of camera and position of telescope on a mount, and greatly reduces stresses on bearings and motor drives.

If your main objective is for astrophotography, the do get a purpose made and substantial motor driven EQUATORIAL MOUNT.

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22/02/13