Eyepiece projection
The eyepiece projection is a method in amateur astronomy for astronomical observation, in which an eyepiece is used to project the image of the observed object onto a screen or a photographically sensitive surface. She will v. a. used in observing the sun and in astrophotography .
For the safe observation of the sun with the telescope , the sun image is projected onto a screen attached behind the telescope. This procedure, which was already known to Galileo Galilei , is not only safe, but also enables the image of the sun to be easily drawn and simultaneous observation by several people.
The eyepiece projection lies between the two variants just discussed because two lens systems are used here. As with focal projection , the lens of the telescope creates an image. This is projected onto the camera's chip by the second lens system, the telescope's eyepiece.
When observing the sun, make sure that no eyepieces with cemented lenses are used, as the cement can heat up to such an extent that the eyepiece is damaged. Huygens eyepieces are therefore particularly suitable . Additional protection is provided by solar filter foils that are attached in front of the telescope opening and thus reduce the sunlight to a safe level before it reaches the telescope. This means that mirror telescopes are also suitable for observing the sun.
With eyepiece projection in astrophotography, the screen is replaced by a camera . The image is either projected onto a chemically developed film or onto the CCD sensor of a digital camera .