Rob's Amateur Astronomy Guide

Astrophotography is a challenging subject. With advances in technology, it is now possible for the amateur to take visually pleasing images of space. There are several types of photography possible for the amateur; these are:

For serious astrophotography, a solid equatorial mount with dual axis drive is recommended. Equatorial mounts with motor drive enable the telescope and camera to move at the sidereal rate so deep space objects, such as stars, nebulae and galaxies appear to remain stationary. Widefield, deep space imaging is possible by mounting the camera directly on some type of equatorial mount, such as a German Equatorial Mount, or home made Scotch Mount. Dobsonian and fork mounts are suitable for planetary imaging, but not deep space imaging, unless some form of equatorial wedge is used.

This is the conventional method of astrophotography that has been around for over 50 years. Film is so unlike the electronic digital methods of today. The 35mm SLR method is probably the lowest cost way of getting into serious astrophotography. A 35mm SLR camera with full manual settings is required. The camera does not require a working exposure meter, as exposures will be set manually using the shutter speed setting. These can be obtained second-hand. The photo lens of the camera is removed and a T-mount with T-ring for your specific brand of camera is attached to the lens mount. The T-mount slides into the 11/4" or 2” focuser on refractors and Newtonians. On SCT the T-mount is usually attached to the visual back of the telescope.

On Newtonian telescopes, the SLR camera can be attached directly to the eyepiece using an eyepiece projection adapter. Simply by changing the eyepieces, the magnification of the object is also changed. No further adjustment of the mirror position is required with this method. With standard T-mount adapters and Newtonian telescopes, there is generally some further adjustment necessary to obtain focus at the camera. Usually the adapter needs to be closer to the primary mirror than the focuser allows. This requires the primary mirror to be moved closer to the focuser. If you have a Newtonian telescope designed for astrophotography, you are very lucky indeed, none of these adjustments are necessary.

The best type of film for astrophotography is 35mm 400 ASA slide film, such as Kodak Elite Chrome or Fuji Sensia. This type of film provides the best sensitivity (light gathering ability), color reproduction and resolution (graininess). Print films can also be used, especially for planetary photography; however, they generally require special processing to bring out the correct colors and exposures.

Most astrophotographers now use digital SLR cameras or dedicated astro CCD cameras. Canon DSLR's with the Baader UV/IR filter modification are the most popular type of DSLR. The digital SLR camera is attached to the telescope focuser using a t-mount and t-ring. Exposures are set manually using the bulb setting. ISO settings are generally set to ISO 400, 800 or 1600, depending on the object being photographed. Usually the camera is controlled by computer software on a laptop. The software also allows the camera to be accurately focused. Guiding is required for long exposures and is also controlled by the laptop at the same time as imaging. Usually tens of light sub frames are taken of a particularly object and later stacked to produce a final image. Stacking images reduces noise and improves exposure of the final image. Once, imaging is complete, calibration sub frames, consisting of darks, flats and bias frames are taken to improve the quality of the final image. The calibration files are processed at the same time as the light frames are stacked.

These are specialized cameras designed specifically for astronomy. The CCD chip is designed for long exposures with builtin cooling to eliminate dark current noise. They are generally software controlled, requiring connection to a PC and are capable of high resolution images.

Coupling of the CCD camera to the telescope is usually via a c-mount or t-mount adapter. Coupling configurations are the same as for SLR cameras, with the adapter either sliding into the focuser for prime focus imaging.

Image capture and processing is similar to digital SLR cameras; however, if monochrome cameras are used, separate LRGB sub frames are taken and later combined to produce a final color image.

A cheaper alternative to enter the realm of digital astronomy. Web cams are low cost and can generally be modified to adapt to a telescope by replacing the front lens with a web cam telescope adapter. Web cams are used for imaging the moon and planets.

One type, the Meade Lunar and Planetary Imager is a webcam type digital camera with exposures of upto 16 seconds. It is a high quality, low cost imager for the moon and planets. The Meade Deep Space Imager is a long exposure webcam type digital camera. Both Meade cameras use the Sony HAD chip.

Another ccd camera, the Imaging Source DBK21 is one of the most popular for planetary imaging.

Camera	Type	Recommended Use	Cooling
Video Eyepiece	Astrocam	Moon	No Cooling
Phillips Toucam Pro	Webcam	Planets	No Cooling
Atik	Astrocam	Planets and Deep Space	Peltier Cooled
Celestron Solar System Imager	Astrocam	Planets	No Cooling
Meade LPI	Astrocam	Planets	No Cooling
Meade Deep Sky	Astrocam	Planets and Deep Space	No Cooling
Imaging Source DBK21	Astrocam	Planetary	No Cooling
Orion Starshoot	Astrocam	Planetary and Deep Space	Depends on Model
QHY	Astrocam	Planetary and Deep Space	Depends on Model
Canon DSLR with Mod	DSLR	Deep Space	No Cooling

Most astro CCD cameras come with a 1.25" nosepiece or t-mount for attaching to the telescope focuser. Some cameras require a seperate adapter.

A C-mount camera is attached to the telescope 11/4" or 2" focuser with a c-mount adaptor. The standard c-mount adaptor is a basic mechanical adaptor with thread diameter of about 25mm and without any optics for work at prime focus.

The 35mm SLR camera adaptor or "T-adaptor" is attached to the 11/4", 2" focuser or visual back (SCT). This adaptor usually has two components:

1. The main adaptor body with a standard 42mm screw thread on one end and 11/4" or 2" tube on the other end.

On SLR cameras, the usual type of lens mount is the bayonet mount. There are several types of bayonet mounts peculiar to each manufacturer. The front lens of SLR cameras is not used for astrophotography, instead, a t-ring is attached to the cameras bayonet mount to the telescope adaptor. With automatic SLR cameras, you will find the electronic signal transfer system does not work with T-mounts. In fact all SLR cameras with automatic exposure rely on the electronics in the front lens to set exposures. As T-mounts do not use the front lens of SLR cameras, this feature will not work. When using SLR cameras on a telescope, exposure needs to be set manually, using the camera's shutter speed knob or bulb setting. If your camera does not have manual settings, then it is probably unsuitable for astronomy use.

Astrophotography and CCD Imaging