::Interactive Astronomy::

Telescopes | Binoculars | Astrophotography

Astrophotography

This is a hobby of many astronomers. In essence, it is the capturing of photographs of the night sky, of the stars, constellations, moon and planets.

Astrophotography requires an SLR camera with a time exposure setting ('B' setting) mounted on a steady tripod. Normal film would not be sensitive enough to record the faint light reaching us from the stars light-years away in the 1/250th second that the shutter of a conventional camera operates. Therefore, the shutter must be open for a longer period of time to allow the light to build up on the photographic negative.

Although more bulky than other types of cameras, these are most versatile as their 'B' setting allows time exposures to be made instead of an automatic shutter opening for a few seconds. They are often used with a cable release to minimise vibration and are attached to a tripod to prevent unnecessary shaking which may blur the image

Camera and Tripod Technique

This method involves a SLR camera mounted on a tripod. It has either zoom lens in front or wide-angle lens. It also requires a cable release to reduce the vibration when the shutter is depressed

Here is a guide for the Camera and Tripod Technique that would help you take photographs better; the quality of the photos would depend on the ISO speed rating of the film (the higher the ISO speed, the more sensitive it is to light) and the quality of the air and weather: All of the items mentioned here are using !SO 400 film without zoom lens.

Subject	Declination from celestial poles	Time exposure
Moon	Along the Ecliptic	1/500 (full moon) to 1/150 second
Planets	Along the Ecliptic	2 to 4 seconds
Constellations	0 to 45 degrees 45 to 60 degrees 60 to 90 degrees (90 degrees implies celestial equator)	40 secs 30 secs 20 secs
Star Trails	Nil	1 min to 2 hours

Note: Time exposures should be kept to under 2 minutes in Singapore as the light pollution build-up would mar the images.

Deep-Sky Piggyback Technique

This method makes use of the robotic motors of a telescope mount to allow the camera to track the stars. It allows long exposures of up to 30 minutes to be made compared to the maximum of 50 seconds for the camera and tripod technique.

Prime Focus Technique

This method allows images of higher magnification be taken as the image is through the telescope. However, the disadvantage is that not only are adaptors needed (extra cost), guiding the telescope is also a must to ensure that the image does not go out of the field of view due to minor inaccuracies in every telescopic mount.

This technique makes use of an appliance called the T-ring to attach the camera body to two different types of adaptors to the telescope body. The advantage of this is that it allows the image to be magnified greatly.

Telescopes | Binoculars | Astrophotography