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 sky objects, such as stars, nebulae and galaxies appear to remain stationary. Widefield, deep sky 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 sky imaging, unless some form of equatorial wedge is used.

This is the conventional method of astrophotography that has been around for over 50 years. It is a pleasure using film and SLR cameras, 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. These can be obtained secondhand or new. 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" focuser on refractors and Newtonians. On SCT the T-mount usually attaches to the visual back of the telescope. The camera does not require a working exposure meter, as exposures will be set manualy using the shutter speed setting.

To obtain images of varying magnifications, the SLR camera can be attached directly to the eyepiece using an eyepiece projection adaptor. This method is generally simpler and more effective for all types of astrophotography. Simply by changing the eyepieces, the magnification of the object is also changed.

With standard T-mount adaptors and Newtonian telescopes, there is generally some further adjustment necessary to obtain focus at the camera. Usually the adaptor needs to be closer to the primary mirror than the focuser allows. This requires the primary mirror to be moved closer to the focuser. Instead of making changes to the telescope, use a camera adaptor that does not require this adjustment. There are several eyepiece projection adaptors (see Scopetronix in links section) on the market that attach directly to the eyepiece and reach focus normally or with a small 1-2" extension to the focuser, or add a Barlow Lens between the camera and focuser to reach focus.

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), colour 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 colours and exposures.

These are specialised 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 adaptor. Coupling configurations are the same as for SLR cameras, with the adaptor either sliding into the focuser for prime focus imaging, or attaching to the eyepiece for eyepiece projection imaging.

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 adaptor. Currently, there is really only one webcam on the market of sufficient quality for astronomy use. This is the Phillips Toucam Pro. Web cams are used for imaging the moon and planets. A modification to allow for long exposures is available. Several other webcams have been used with success, including the Quickcam 4000 pro and 3000 pro. However, the quality of the CCD chip is not reliable from one camera to another.

Retail digital cameras are better quality than web cams. They are also limited to short exposures for the moon and planets. A special digital camera adaptor for eyepiece projection imaging is usually required, although simply holding the camera to the eyepiece and focusing at infinity can also work.

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, planets and brighter deep sky objects. The new Meade Deep Sky Imager is a long exposure webcam type digital camera. Both Meade cameras use the Sony HAD chip. The Atik CCD Camera is a modified web cam based astro camera that uses the Phillips Toucam Pro chip. This camera allows unlimited long exposures.

Camera	Type	Recommended Viewing	Cooling	CCD Format
Video Eyepiece	Astrocam	Moon	No Cooling	1/4"
Phillips Toucam Pro	Webcam	Planets	No Cooling	1/4"
Quickcam 4000	Webcam	Moon	No Cooling	1/4"
Atik	Modified Webcam	Planets	Fan Cooled	1/4 and 1/3"
SAC 4	Astrocam?	Planets	No Cooling	1/2"
Celestron NextImage	Astrocam	Planets	No Cooling	1/4"
Meade LPI	Astrocam	Planets	No Cooling	1/4"
Meade Deep Sky	Astrocam	Planets and Deep Sky	Cooled Using Unique Design	1/4"

A C-mount camera is attached to the telescope 11/4" 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. Many professional astro cameras use this method.

The 35mm SLR camera adaptor or "T-adaptor" attaches to the 11/4" 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" tube on other.

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 photomicrography, instead, a t-ring attaches the cameras bayonet mount to the microscope 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. If your camera does not have manual settings, then it is probably unsuitable for astronomy use.

Most professional digital astro cameras use a c-mount for attaching to a telescope. It has become popular, however, to use retail digital cameras for imaging through a telescope as they have a lower cost and produce high quality images. Retail digital cameras have non-removable front lens and a special digital camera adaptor is required to attach the camera to the telescope. The adaptor usually attaches to the eyepiece on one end and to the filter threads on the front lens of the camera at the other end. Some adapters do not attach the eyepiece, but slide directly into the 11/4" focuser. This is the case with webcams, where the front lens of the webcam is removed and replaced with a special webcam adaptor (see ATM links).

Astrophotography and CCD Imaging