ARCturus

The digital cameras have for years been successful in capturing market shares, but a mechanical camera is still a usable device in astrophotography. It has many useful functions which cannot easily be carried out with a digital camera. Since there only are a few parts that need electricity to function, the mechanical camera can also be used in temperatures below zero. In the picture, a mechanical camera has been fixed into a self-made monitoring device (design S. Ekko, picture IH, Finland).

 

Aim: To get to know the options that the mechanical camera offers in astrophotography. To learn to select the optional settings for enabling the best possible quality.

 

Explorations: Discuss with the students cameras and astrophotography on a general level developing at the same time ideas for implementing a common astrophotographic project for the class. Since the assortment of cameras is not scarce, it is worthwhile to concentrate on only one or two types of cameras. Happy are those schools that own a camera equipped with an objective suitable for astrophotography and can make it available to the students.

 

1)  Get together and familiarize with the camera the school has acquired. Find the most important selectors, such as location of the film, focal control, adjusting of sensitivity and exposure time, as well as the aperture selector. Find out if there is an option for a cable release.

 

2)  Continue equipping the camera. Discuss first the acquisition of a film. There are many film types for various purposes. Black and white films as well as colour films have various speeds. The speed most suitable for astrophotography is ISO1600. Pictures that are printed on paper and can be further processed in a digital form are nowadays the most popular. Slide films are not used so much anymore. One of the reasons for that, no doubt, is the fact that the moderate-speed slide film, the most suitable for astrophotography, is nowadays rarely included in the assortments of the shops.

 

In astrophotography the exposure times tend to be long because the objects usually are very dim. With the help of a cable release attached to the mechanical camera, the photographer can easily adjust the exposure time to reach the best possible result. Before taking photos there are two things to remember: turn the exposure time selector to exposure override and the film speed selector to match the film speed. Taking photos of the dark sky needs a maximum possible amount of light. To ensure this, the biggest aperture size, i.e. the lowest value in the dial, should be used. If the objects are bright, such as the moon, it is worthwhile to consider using a smaller aperture size. Experienced photographers and literature may be of help and give hints for the choice.  Taking photos of far-away objects, such as the stars, the distance scale selector should be turned to ‘infinite’.

 

3) Explore with the students the basic facts and control panels of the camera. Rehearse the use so that every student learns how to handle the camera in a smooth manner. Use old film to practice the loading and unloading of the film. This know-how is especially important in case the film needs to be changed in the darkness of the night outdoors.  Let the students practice photography by providing them with a few films. Change the aperture size, distance scale and exposure time in turn. Write down the choices of each picture. Knowing the choices made, evaluate the pictures and make adjustments needed for further shootings.

 

4)  Taking photos of dim objects demands a long exposure time. During that time, the stars draw their paths on the film because of the rotation of the Earth about its axis. This problem can be solved by fixing the camera into a monitoring device. With the help of its indication marks, the axis of the device can be set to point to the Stella Polaris, i.e. to be parallel to the axis of the Earth. The device is either turned manually at a speed previously tested or it turns electronically. It allows the positions of the stars to remain dots even when the exposure time is longer. However, if it is the aim to take photos of the paths of the stars, the monitoring must be switched off. Due to the longer exposure time the paths of the stars are seen as bright lines in the picture.

 

5) * Offer the most enthusiastic students a chance to take photos of some special cases. Expose the western and eastern sky over the horizon for a long time without any monitoring activity. The result is very interesting. The paths of the stars are straight lines on the equator level but they curve on both sides of the equator away from it. When the photos are taken from the Stella Polaris, and no monitoring is used, the paths of the stars are nested circles around the Stella Polaris.

 

6) * The photos showing the paths of the stars can be used in the classroom as a basis for pondering and solving many mathematical exercises.  The angle between the equator lines and the horizon is known. It gives an option to find out the latitude of a place. The circle lines can act as an indicator in determining the rotation speed of the Earth, provided that the exposure time is taken into account. Changing variables produces more mathematical exercises for the students.

 

7) * Use the Internet to find more information on cameras, their quality and accessories. Explore an option to connect the camera to a computer and convert the pictures into a digital form right from the beginning. It is easy to take more pictures by adjusting the settings of the camera. Ease of use encourages the students to take further steps in astrophotography.

 

Methods: Becoming familiar with the parts, adjustments and accessories of a camera. Taking photos in various circumstances in nature. Making use of the results in extra tasks.

 

Materials: Camera, monitoring device, films, accessories, program for processing photos.

 

Pondering: Discuss the circumstances during the astrophotography, such as weather, amount of light and light pollution. Ponder whether there is a need for filters.

 

Evaluation of the results: Compare the photos taken in various situations and with various adjustments. Browse the preliminary snapshots and find issues which show a lack of know-how and a need for improvement. Take careful notes of the photographic circumstances and adjustment values used.

 

Hints: It is worthwhile to have a lamp shedding red light when taking photos in the dark night. Every now and then, it is necessary to check the adjustments and change them if needed. A white light disturbs the eye for long and prevents it from accommodating to the darkness.

 

Keywords: Camera, film, astrophotography, exposure time, film speed, ISO, monitoring device, aperture size, objective.

 

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