Ken Hough's Website
Astrophotography

Long Exposures

The Need For Long Exposures:
With the notable exception of the Moon, most celestial objects are not very bright. To record images properly, exposure periods from a few seconds to over 10 minutes might be needed. For the longer periods AUTOGUIDING might be needed.

It is important that no slippage occures between telescope, camera, or mount components. All must be well "locked down". Care must be taken that no external parts or connections can impose forces on the assembly. If possible loop all camera connections so as to pass out near to the central support of the mount rather than allowing them to trail down from the end of the telescope.

Long exposure astrophography is very demanding of equipment. Use a robust/stable mount, which must of course be a motor driven EQUATORIAL mount that has been accurately aligned to the celestial pole.

Stacking Of Images:
Instead of applying very long exposures, several shorter exposures can be taken which are then "stacked" via a computer to produce a single image. Possibly the most popular software for this job is RegiStax.

"Stacking" of images can have sometimes have advantages over a single very long exposure:

-- Can reject images containing aircraft trails and other undesirable artifacts.
-- Shorter exposure are less demanding of tracking accuracy.

Camera ISO Setting:
Modern digital cameras can achieve high ISO speed settings. However, the higher settings are intended to be used for typical terrestrial situations. Astronomical situations often require that shadow tones are selectively enhanced, which of course also increases the effects of digital noise. If possible try to keep ISO settings below ISO 1000.


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22/02/13