From Glass Plates to Electronic Sensors, Astro Imaging Has Come a Long Way

We recently received our latest newsletter from the team at iOptron and it included a nice overview on the history of astro imaging. We enjoyed the article and thought you would as well.

Image captured in 1974 with a fairchild 100 x 100 pixel camera launched the CCD era of astrophotgraphy.

From around 1850 to the early twentieth century the discipline of astrophotography traversed many milestones. Changes in equipment, technique and processes all played significant roles in the expansion of interesting objects that could be photographed. Using the “great” 38 cm Harvard refractor, in 1850 John Whipple and William Bond were the first to successfully photograph a star. The image of ɑ Lyrae, Vega was captured in a 100 second daguerreotype exposure.

Seven years later, in capturing the first successful image of double stars (Mizar and Alcor) George P. Bond (son of William Bond)  employed an entirely different medium to capture the image. Commonly called “wet plate”,  collodion is a mixture of nitrated cotton dissolved in ether and alcohol.  The substrate is then spread over a glass plate on which the image would be projected.  The process itself was far less expensive than the daguerreotype and being a negative/ positive process, it permitted unlimited reproduction.

As things moved forward, the variety of celestial objects  photographed increased exponentially.  In 1857 Jupiter and Saturn are imaged, 1880 M 42 Orion nebula, 1881 comet Tebbutt, and many more to follow.  For the first time in history, the masses were able to view the splendor of the cosmos through photographs.  Even today, the majority of the world’s citizens have not had the opportunity to look through a telescope, yet most have seen astrophotos in books, magazines and computer screens.

Throughout the 20th century, a number of factors significantly improved photographic results. Improvements in optical design, mount stability, tracking accuracy and photo process enabled astrophotographers to capture images of high scientific and aesthetic value.  As images improved so did their expectations, imagers continued to tinker with capture technique and image process.

A particular property of film, its loss of light sensitivity with lengthier  exposures, is a significant obstacle for astrophotgraphers. Exposures on film of one second or less, tend to result in a linear relationship regarding time and light sensitivity.  However, exposures of longer duration shift to an exponential relationship  requiring much longer exposures to gain incremental amounts of light (reciprocity failure). Innovations such as “cold cameras” helped but did not alleviate the short comings of film. In 1969, the development of the CCD would soon give astrophotographers the imaging medium they had for so long sought.

It didn’t  take long for the value of a CCD’s ability to evenly gather light over time to be recognized by astrophotographers.  Early CCD images were “pixilated” and lacked definition, however exposures times only took a fraction of what was needed for film.  CCD technology improved exponentially through its first few decades of existence.  Today, the application of CCD technology is prevalent in the astronomy  community.  Amateur astroimagers worldwide are capturing and processing images unimaginable to pioneers of only a century past.

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