Celestron"s deluxe tele-extender is a high-power photographic accessory for Schmidt-Cassegrain telescopes. It"s a hollow tube that allows you to attach a camera to your telescope with an eyepiece installed. By using the Deluxe Tele-Extender in combination with an eyepiece, you can increase your telescope"s effective focal length to well over 10,000mm! And with this comes a corresponding increase in image size. It"s a technique known as eyepiece projection photography, and it multiplies magnification by the distance from eyepiece center to the film plane, according to the following formula: Effective Focal Length = Telescope focal length ? Eyepiece focal length X DF (distance to film). The deluxe tele-extender is used for high-power lunar, solar and planetary photography as well as for extreme terrestrial photography. To employ the tele-extender, remove the diagonal from your telescope and insert an eyepiece directly into the visual back. Place the Tele-Extender over both the eyepiece and the visual back and attach your 35mm SLR camera to the back of the tele-extender, using a T-ring. That puts you in business for fine, highly magnified astrophotography! Note: The image you"ll see through your camera"s viewfinder will be upside-down. And, because of the extremely high magnifying effect afforded by the deluxe tele-extended, you"ll want to take extra care to prevent camera and telescope vibration. Accurate polar alignment and using only under good seeing conditions will also help you capture high-quality images. The deluxe tele-extender is only for Schmidt-Cassegrain telescopes! * For Schmidt-Cassegrain use only * Allows you to attach camera to telescope with an eyepiece installed inside Tele-Extender * For Eyepiece Projection photography * Used for high-power lunar, solar or planetary photography * Must be used with T-Ring for your appropriate camera