About

What is Astrophotography?
Astrophotography, as the name implies, is a specialised form of photography that involves taking pictures of astronomical objects in the night sky. As astronomical objects are generally quite faint and often small in angular size, a type of magnification usually through a lens or telescope is required. Frame composition, focusing and shooting are not performed by the simple “point and click” method commonly used in terrestrial photography. As the object being photographed is faint, it is near impossible to perform composition and focusing through the camera viewfinder. Various tools, techniques and experimentation are required to resolve some of these obstacles.

Astrophotography is perhaps the most demanding form of photography. There are numerous components that need to work together when creating an astro photo or image. The following briefly explains these;

Mount – The motorised mount should be capable of accurately tracking the motion of the night sky ensuring the object stays within the camera’s field of view. Careful attention to minimizing backlash (delayed opposite direction movement of the mount gears) and periodic error (manufacturing defects of the worm and associated gears) are vital. The mount carrying capacity should be ample to carry the optical tube (telescope), camera and other photographic accessories. An overloaded mount is sure to provide poor tracking performance. Finally, the mount should be polar aligned with the celestial pole to enable long exposure astro photos or images. The criticality of alignment is based on the telescope focal length. A longer focal length instrument will require better alignment than a short focal length.

Optical – The optical tube should suit the type of object being photographed or imaged. Solar system objects require high magnification delivered by long and slow focal lengths. In comparison a majority of deep sky objects such as galaxies and nebulas are best suited to faster focal lengths. This allows the camera to capture a large field of view and as much detail possible in the shortest period of time.

Camera – The camera should be capable of locking the shutter open for a long period of time(bulb setting). If using film emulsion, ensure it has low light sensitivity. Gas hypersensitising of emulsion can improve sensitivity. The availability of CCD astro cameras have revolutionised astrophotography with exceptional light sensitivity and low digital noise. Vastly different from digital SLR cameras, the CCD astro camera is cooled below freezing point, reducing noise and usually have a quantum efficiency of 80% at the 650nm wavelength light emissions prominent in nebulas and galaxies. The CCD astro camera should match the focal length instrument to optimise how many pixels cover the sky. Despite the clear benefits of using CCD cameras some astrophotographers continue to use film due to its aesthetic looks and warmth.

Focus – The camera needs to be located at the focal point of the lens or telescope. Precise focus is required otherwise the astro photo or image will display soft features and lack detail. As previously mentioned, faint objects will be invisible through a 35mm camera viewfinder making focusing difficult. Digital and CCD cameras have the advantage of displaying the image on a computer to confirm critical focus. Motorised focusers are ideal as they can reproduce exact focus time again and move in small steps, not easily achieved when focusing is performed manually.

Environmental – Obviously taking photos or images of the night sky while cloud cover is present will not provide pleasing results, but having a clear sky is simply the beginning. Issues such as atmospheric turbulence and light pollution can significantly degrade the image or photo quality.

This may appear quite technical, complex and sound like a lot of money and effort. However, it need not be. Simply setting up a fixed tripod with an old 35mm SLR camera operating in bulb mode can deliver stunning results of star trails as they swirl around the celestial pole. Even seasoned terrestrial photographers will be in for a surprise at the technicality of this form of photography. Many astrophotographers state that data acquisition is the easy step in creating a great astro photo or image. The real work begins in post processing using desktop digital imaging tools to bring out the exquisite detail of dust and nebulosity. If you desire to advance in astrophotography pursuits, be prepared for some steep learning curves. You will have many failures along the way so documenting every exposure will accelerate success. Have fun and good luck!

An early history of Astrophotography

"When you take a photo, what are you offering the world?  Just as a musician must have the sense to make his own music, the photographer must have the imagination to see something beyond the scenery.  And for that, the photographer can only look into himself.  When he does, he will fly.  Look at the stars, but fly with your imagination.” - P.K Chen