INSTRUMENTS

ASTRAL TELESCOPE

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PHOTOGRAPHIC USE

FOCUSING WITH THE CAMERA
The focusing process is carried out in much the same way as when you are using a telescope with oculars (except in the case of parallel photography). The difference is that in this case the clarity of the image depends on the transparency of the focusing screen. This is better in professional cameras, and somewhat darker in cheaper cameras. In any case, the central part of the image will be dark because of the reduced brightness (when compared to a normal objective) of the telescope. It will always be opportune to use brief exposure times in order to avoid "wavy" images of little sharpness.
The exposure can be determined with an exposure meter incorporated in the camera itself.
Remember that the telescopes are not equipped with regulatable diaphragms. With experience, you will be able to decide the time required for what you need. It is worth heeding this piece of good advice: take different shots of the same object using different exposure times. Some autofocus models, used without an objective, require an estimated setting out of exposure rimes. For more precise information read the instructions manual accompanying the camera.

ASTROPHOTOGRAPHY
Photography of the Moon is relatively easy and offers worthwhile results even after early attempts. It is important to use a well-balanced instrument and to ensure that the camera has an automatic shutter release (to count the vibrations). Focusing should hot present any problems. The choice of film depends on taste. Excellent results can be obtained with black and white films (these, however, need to be developed and printed by experts) or with slides of middle to low sensitivity. Here follows a table with exposure times, relative to the lunar phase and to the type of film use.
The focal length influences the dimensions of the objects that are registered on the film. At a focal of 1000mm, the dimensions of the moon on the negative will be about 9mm, sufficiently large, whereas those of the planets will be only hundredths of a millimeter and therefore unusable. It will be necessary, therefore, in order to photograph the planets, to use a special connection for projection photos which will give the telescope the necessary focal to obtain planetary images of appreciable size (see the General Notes Manual).

The focal of the ocular will be chosen on the basis of the size of the object and the dimensions of the image you wish to obtain. In order to know the dimensions of the planets (in millimeters) from the images that will be obtained with the various oculars, you will need to apply the following formula:

The angular dimensions of the planets are variable according to their position in the orbit with respect to Earth, and their value can be ascertained by consulting an Astronomy Almanac.