Digital Imaging Trends in Consumer Astronomical Photography

Since the launch of the Hubble Space Telescope there has been widespread popular interest in astronomical imaging. A further series of events, most notably the recent Deep Impact mission have served to fuel further interest in this. In parallel with this there have been a number of events and trends that have increased interest in astronomical photography outside of professional astronomy. Advances in imaging hardware have made a significant contribution over the past few years. This paper will examine these advances with examples of state of the art imaging systems. The paper will conclude with some potential trends for the future. Introduction The past 15 years have seen major changes in consumer astronomical photography. New telescope designs have promoted explosive growth in the availability and performance of astronomical telescopes for the consumer market. This is now a significant market with annual global sales to the advanced consumer market (telescope apertures of ≥ 150mm) estimated in 2004 to be $40 million1. These technologies have now developed to an extent that they are also ready for use in other imaging applications. The combination of these telescopes and new electronic imaging devices allows amateur astronomers to now produce some stunning images2. These technologies, beginning with the telescopes, are summarised in this paper. Telescopes The layman’s impression of a telescope is a unit that looks something like Figure 1, a refractor that can be traced back to the original design attributed to Lippershey and used by Galileo. Of similar ancestry is a reflecting design attributed to Isaac Newton. Reflecting telescopes generally employ a mirror made to a parabolic figure. This has the advantage that all rays parallel with the optical axis converge to the focal point, irrespective of the position they are incident on the mirror. However, the manufacture of parabolic mirrors of the required tolerance is difficult and expensive and they are prone to substantial geometric aberration in the form of coma towards the edge of the field. Moreover, the coma is more pronounced as the focal length of the mirror is reduced so large focal lengths and hence long telescopes were required. Coma causes the image to be degraded away from the central field of view, and the usable field size for photography is limited, especially in short-focus instruments. The above problems are overcome by using a spherical figure for the primary mirror. Spherical mirrors are easier and cheaper to manufacture and do not suffer from coma, making them very suitable for imaging purposes. However, they Inside This Issue Digital Imaging Trends in Consumer Astronomical Photography ........ 1