Test lens for SBIG cameras

Accessory Lens for
ST-7/8/9/10/2000 Cameras
List Price $29.95
October 17, 2003

The 25mm F/16 lens assembly screws into the t-thread ring of the camera

This inexpensive test lens allows the user to become familiar with CCD camera operation and software in the comfort of his home, without a telescope. The lens is very modest – it is a double convex plastic lens with a focal length of 25 mm and an aperture of 1.5 mm (F/16), in a metal housing with a T-thread on the outside. It forms an image that is good over an area about 7 mm in diameter, and deteriorates gradually outside of that. The lens can be used to take pictures indoors under typical office or home artificial lighting illumination with exposures of 0.12 seconds, or longer exposures under dimmer conditions. Daylight is too bright and rooms with windows open to bright daylight will saturate the CCD. It is therefore best to close any curtains and use only artificial light when testing. If one just sets the camera-lens combination outside on the ground looking up, images of the constellations can be taken up to 10 seconds long before the earth’s rotation elongates the image. Stars down to 6th magnitude will be recorded.

A 30 sec image of the sky taken with an ST-10XME using the Accessory Lens

Use of the Lens

To use the lens, remove the nosepiece from the camera, and screw the test lens into the T-ring on the front of the ST-7/8/9/10/2000 camera. The flat surface should be outward (away from the CCD). Screw it in about an eighth inch (3 mm), start FOCUS MODE on the camera, and frame and focus some convenient object. Focus by screwing the lens in or out. The depth of field is large. When focused, one can then GRAB an image, and adjust the background and range of the displayed result to optimize the appearance.

Matt as seen by ST-10XME with Accessory Lens

Limitations

This lens is not a substitute for a quality imaging lens. The images are only intended to be used for the purpose of testing the functions of the camera. The lens cannot be used to image a daylit scene – the camera will saturate in the shortest exposures. Also, do not try to image the sun during the day – the CCD may be damaged. The lens is really intended for indoor use, for practice in using the camera before attempting imaging at the telescope.