 |
The Multi-Schiefspiegler telescope can be used for astrophotography. The easiest way is to get images at the prime focus. Therefore you can attach a flip mirror camera, a video-camera or a CCD camera to the focuser and focus until you get a sharp image at your camera finder.
For extended objects you have to consider that the field of view without any vignetting is limited to 0.5° (for Wolterscope 150 f/11). This corresponds to an image of 14 mm diameter at prime focus. Therefore you might see some intensity loss towards the edges of a photographic film (it covers an area of 24 mm x 36 mm). The image plane is also tilted by about 1.5° with respect to the film plane and there exist a very small curvature of the image plane. These optical effects can be neglected practically.
To focus the image you can use the aperture mask to analyse the image of a bright star. To get a sharp image, look through your camera finder and find a position of the focuser, where the separated light points merge together into a single point.
Lock the screw ontop of the focuser to fix its position and than turn the scope to your object of interest and remount the aperture mask.
To attach a camera you will need a special adapter ring which can be purchased from traders for astronomical equipment. The focusers end owns a T-thread and you need a T-ring adapter which fits to your special camera mount.
Bright objects (like moon and planets) can be imaged by using eyepiece projection. The image at prime focus will be enlarged by the eyepiece and the camera is mounted a certain distance behind the eyepiece. Therefore you need a special tube for eyepiece projection. Available are tubes with a fixed length and tubes of variable lengths. The latter allows to use different image scales, because the distance between eyepiece and camera can be varied.
To get the right exposure on your film you should take a series of photographs and double exposure time from picture to picture. You should also use a remote control wire to avoid any movement of your telescope and camera.
Another way to get a larger image scale on your camera is to use a Barlow lens in front of your camera to multiply the focal length of your telescope by the factor of the Barlow. You can also combine a Barlow lens with an eyepiece and perform eyepiece projection.
You can also use a Digital camera for imaging bright objects. The camera should be attached behind the eyepiece by using a special adapter ring. Some amateurs got images of moon and planets simply by holding the camera by hand behind the eyepiece. The eyepiece should be of good optical quality and possess a long eye relief, otherwise some vignetting might occur at your image. Some cameras a more suited for astrophotography than others. This depends on light sensitvity, noise reduction and also on the construction of the camera photolens. To get an unvignetted image the exit pupil of the eyepiece should be positioned at the field aperture of the photolens and its diameter has to be smaller than the aperture stop. This condition can not always be fulfilled.
|
|
