Astrophotography techniques for film cameras
From the very early days of photography and on, man turned his telescope to the moon and the distant stars to capture the beauty of our universe on film. Astrophotography is now a separate discipline on its own and high quality images require considerable investment in high technology equipment. However, it is possible to make pleasing images of the night sky with an amateur film camera, without a need for much spending.
In this article, you will discover simple procedures to shoot the stars, making use of your film camera, learn which lenses and films work best, as well as basic tips.
As for film cameras go, any brand or model will suffice, however the information in this article focuses mainly on 35 mm photography.
The right location
Photographing the night sky starts with favorable atmospheric conditions. In big cities there are simply too many lights that reflect in the sky and obscure a great deal of stars. This is called "Light Pollution" and must be prevented in order to expose a clean image. The only practical solution is to go out in nature where one can be able see the milky way with bare eyes. Another factor apart from having cloudless skies is the amount of water vapor and haze. Summer nights can be cloudless, but the heat may cause a slight veil of haze at low altitudes close to water. In contrast, the sky is free from haze in wintertime, and although it may be cold, it offers a better setting for stargazing and astrophotography.
The right lens
Every lens has a maximum capacity to gather available light, which is determined by the surface area of its front-most element. Though the human eye can be considered the best optics in terms of color definition and image sharpness, the pupil of the eye is in average about 7 mm when it is wide open. In comparison, the front-most element of a 50 mm standard lens with a 1.4 aperture has a surface diameter of about 50 mm. Therefore, a lens of such a diameter will gather more light than the pupil of the eye.
A second important factor is the aperture of the lens. A wider aperture (hence a smaller f number) will gather more light. As the lens is stopped down (meaning the aperture is smaller, hence a higher f number), it makes less use of the edges of the front-most element. As an example, a 50 mm f 1.2 lens is considered faster than a 50 mm f 1.4 lens.
So what do these signify? When you are out to shoot the heavens in the middle of the night, you will need the fastest lens you can afford to expose a maximum number of stars on film, as some stars are fainter than the others. If you use a lens with an aperture of 2.8 instead of a 1.4 lens, you will be using half of the available light, and as a consequence the fainter stars will not be exposed enough to show on film.
A third parameter in determining the right lens for astrophotography is the angle of view of the lens. As the earth turns slowly around its axis, the stars will move from east to west, and although this movement will be relatively slow to the naked eye, using a telephoto lens will exagerate this movement, and the stars will move during the exposure producing elongated curved lines instead of individual dots.
In the light of the above information, the best choice is to use a wide angle lens which will not produce elongated lines and which has a wide aperture (a smaller f number) and a front-most element of a bigger diameter. A 50 mm f 1.4 is usually the first choice as it is the cheapest of all faster lenses. However if one is lucky to afford, better choices will be a 50 mm f 1.2, a 35 mm f 1.4 or a 28 mm f 1.4 lens, although they cost much more than a standard lens. Do not forget though, it is always possible to rent one of these lenses from a professional photography store.
The right film
The choice of right film is related to the exposure, and to get the stars as individual dots instead of elongated curved lines, you will need faster films with higher ISO numbers. Commonly used 100 or 200 ISO films will require longer exposures and therefore they will not be much useful. There are however, a couple of films available, specifically designed to be used with low light situations and are good choices for astrophotography.
Both for color and B&W photography, ISO 1600 films will be your best choice. In the past I have used Fuji Provia 1600 color positive film, however it is now discontinued, although one might be still able to find some on E-bay. Fuji still has some fast films in the market though, namely Fujicolor Press 1600 (link) and Fujicolor Superia 1600 color negative films (link) and Neopan 1600 Professional black and white film (link). They both come in 135 rolls and are good choices. Kodak also has an ISO 3200 B&W film in its T-Max product line, and is a reliable film for pushing, can be used in 800, 1600 and 3200 speeds with different granularity results (link). Ilford also has an ISO 3200 B&W film in its Delta product line (link).
Less expensive choices would be ISO 400 films from various manufacturers, but you might need to underexpose and overdevelop them (pushing), and as a consequence you will have granularity and higher contrast.
You should note that using color films for long exposures will result in "Reciprocity Effect", where the three separate color layers in the emulsion will start responding to available light in different degrees and shifts in color may occur. However, these color shifts may also add an expressive touch to the image, rendering the stars in different colors. Reciprocity effect is also prone to noise, and that is one reason to keep your exposure times as short as possible, and necessitates wide apertures.
Long exposures are affected by physical vibrations, and it is important to minimize these vibrations as much as possible.
First and foremost accessory required for long exposures, is a solid tripod. The choice of the tripod will largely depend on the available brands and your budget, however most important aspect of a tripod is its weight as well as its construction. The heavier the tripod, the more secure it will be against vibrations and also it will support heavier cameras and lenses. Tripods with independent legs are good for general photography, but models with interdependent legs are more sturdy for astrophotography. You should also be sure that the tripod will allow you to point your camera at a 90° angle to shoot the zenith (the direction pointing directly above your head), as the atmosphere is thinnest at the zenith at any given location and therefore will have less atmospheric density.
A simple trick to make a tripod more secure against vibrations, is hanging your camera bag or a backpack on the tripod. Just make sure that the additional weight will be well balanced.
Another handy gadget is a shutter release cable which will minimize the vibration at the time of the exposure. In the lack of a shutter release, one can still use the self timer mechanism on the camera. SLR cameras have a mirror to direct the image to the viewfinder, and every time the shutter is fired, the mirror moves up rather fast and adds to the vibration. Some high-end SLR cameras have a mirror lock-up mechanism. Although its use is limited in general photography, it helps reduce the vibration even more. A technique to use in case of a lack of this mirror lock-up feature, is covering the lens with, for example, a hat during the first couple of seconds of the exposure, thereby the vibration from the movement of the mirror will slowly cease, one can than remove the hat and start exposing the film.
A rather small but important accessory idea would be a not-so-powerful key light with a red bulb. When you are in the dark, your eyes will adjust to darkness, and red light will not be too intrusive but handy to see what you are doing. You can easily find one in a dollar store.
Also print yourself a copy of the star chart, so you won't be seeking the skies for a particular constellation :)
Setting up and exposing the film
Once you mount your camera on a steady tripod, adjust your focus to infinity and your aperture to its widest setting (smallest f number). Since the stars are all far enough to bypass the need for depth of field problem, you will just need to use your viewfinder to compose your image. Have a star chart ready, if you would like to photograph a particular constellation.
Exposing the film is a trial-and-error process, however as a rule of thumb an ISO 1600 film will require around 10 seconds of exposure at f 1.4 aperture. That said, you will still need to bracket your exposures by ± 1 increments, meaning taking a shot, than decrease and increase the exposure by half and double the exposure time. I suggest not exceeding 30 second exposure, as the reciprocity effect will kick in, but this will depend on your hardware.
It is a good idea to note the exposure time on a sheet of paper, this will be useful for future reference for a particular film and setting. Write down the focal length and aperture setting of the lens as well as exposure values in seconds.
Summing it up
- Use the fastest wide angle lens available. The wider the angle of view, the more constellations you will be able to fit in your composition. A 50 mm and 35 mm lens is good to isolate one constellation completely.
- Try not to exceed 30 seconds of exposure, or the stars will start showing elongated curved lines.
- Break the above rule, and try making longer exposures. With a wide angle lens you will get an effect of artificial daylight. Use the moonlighting without including the moon in your composition.
- Think of including foreground landscapes in your composition, this will give good results especially shortly after sunset and before sunrise, rendering deep blue and orange colors of the sky.
- Use the self timer on your camera, and cover the lens for a couple of seconds at the beginning of the exposure to minimize the unwanted effects of vibration.
Hope you shoot magnificent images!
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