Sources - Film
Photographic film is a thin, transparent polyester film manufactured with high precision, coated with a light-sensitive emulsion (thickness approx. 5 to 25 micrometers) in a technically complex process in absence of darkness. This emulsion consists of gelatin in which light-sensitive silver salts are embedded. On the finished film, the light-sensitive coating can be seen as a “matt” side and the opposite side of the film can be seen as a “glossy” side.
Photographic films are produced in widths over one meter in a semi-continuous process. Large rolls (several hundred meters) of polyester carrier film are coated in the absence of light. The film is then prepared (cut) differently for the different camera types and packaged so that it is light-tight.
Types of films
The 35mm wide 35mm film (image format 24 x 36mm) corresponds in width to the original cinema film (image format approx. 24 x 18mm). When the image is taken, it is only exposed at a 90° offset from the cinema format. Other common film formats include medium formats (6x6cm / 6x4.5cm / 6x9cm) as well as large format sheet films that are inserted into the camera as individual large sheets (e.g. 4x5 inch, 5x7 inch).
The larger the exposed film area, the more details can be captured photographically. In addition to the resolving power of the lens, the type of light-sensitive emulsion also plays an important role. It makes sense to categorize photographic film types based on the underlying coating type and technology:
Slide film
A slide film (reversal film) is a photographic film that, after development, shows the image in its natural view. This can then usually be projected onto a screen. Reversal films have a coating mixed from different emulsions.
One of the emulsions is highly sensitive, the other is low sensitive. During exposure, the low-sensitivity emulsion is underexposed by about ten times. The sensitive emulsion is now developed with an initial developer - a negative is created. In a second step, the resulting silver is then converted into a soluble compound and removed from the film (bleaching process). The film is then exposed through. The low-sensitivity emulsion is exposed to light. This is followed by further development (secondary or positive development). This creates a fine-grain positive from the developed, low-sensitivity emulsion.
Color reversal films also contain several layers of dyes that are formed on the silver seeds via so-called color couplers. In terms of the basic process and process, color and black and white slide films are developed in the same way.
Negative film
Negative films are photographic films that, after development, have gray values or colors in the opposite (complementary) tonal values. In a second photographic process (enlargement), the tonal value is reversed and the positive image is produced as a print. This can then happen as often as you like. In addition, the photographic enlargement process offers creative possibilities that have been taken up digitally by modern post-processing software (e.g. Adobe Lightroom or Adobe Photoshop).
Black and white negative film
Black and white negative films essentially differ in the type of silver salts used and their light sensitivity (ISO). The latter represents an exponentiated size. A film with a sensitivity of ISO 400 is 16 times more sensitive than a film with ISO 25.
When exposed in the camera, these silver salts are converted into elemental silver by the action of light (silver nucleus in the so-called latent image). This latent image is then reinforced through the development process and thus becomes visible. A distinction can be made between films with cubic structured silver salt crystals and those with flat crystal structures (T-crystals).
The finer the grain size of the salts used, the lower their sensitivity to incident light and the higher the resolution of details of the film emulsion. Light-sensitive films with high sensitivities (ISO 800 to ISO 3200) are therefore “coarse-grained”. In the finished image you can see a present grain structure. Low-speed films with speeds below ISO 200 are “fine-grained”.
In the finished image, the graininess causes what are actually homogeneous gray areas (e.g. sky) to appear interrupted and the resolution is reduced. Therefore, the aim is usually to keep the image graininess as low as possible. On the other hand, graininess can also be used as a design and artistic element. Examples of this include documentary photographs.
The resolution and the sharpness of contours determine the sharpness performance of photographic materials. The higher the resolution, the more details can be imaged. The acutance determines how sharp the contours of this detail are. The greatest possible sharpness of contours is achieved if the light does not scatter into the adjacent shadow areas due to diffraction from the silver salt crystals. This is achieved by thin emulsion layers containing silver salts of fine grain size.
In addition to the panchromatic (all-color) films that are common today, which show all colors as a gray tone, there are also orthochromatic black and white negative films. These are “red blind”, which means that the color red appears as black in the positive.
Other exciting special types of black and white negative films (e.g. infrared films) will not be discussed here due to their niche existence. However, chromogenic negative films should be mentioned, which are developed using the C41 process common for color film and which result in a very fine film grain (e.g. Ilford XP2).
Color negative film
Color negative films differ from black and white negative films in that they are not made of one emulsion layer but of several layers on top of each other. These are usually three layers colored in the primary colors yellow, purple and blue-green. They absorb light colors that complement them. Blue light illuminates the silver salts in the yellow layer, green light exposes the salts in the purple layer and red light exposes the salts in the blue-green layer.
The emulsion also contains color coupler molecules. The final dyes are created by reaction of these color couplers with the color developer on the exposed silver salt crystals. After development, the silver is completely removed, leaving the complementary dyes. The image on a color negative film consists of dyes clumped together. The color negative shows blue light as yellow, green light as purple and red light as blue-green. When developing into a positive, the process is then reversed and a paper image is created with the correct tonal values.
Color films are mainly available in two sensitivity classes: Low-sensitivity films with ISO < 200 and light-sensitive color negative films with ISO > 400. As with black and white negative films, the resolution depends on the sensitivity of the film. The higher the sensitivity, the lower the resolution or the more noticeable the film grain.
Due to the manufacturer's specific chemistry, films reproduce colors differently. Therefore, some are more suitable for landscape photos and others for portrait photos as they better reproduce the tones of the skin. There are also some special types that tend to generate strange colors (for example, by swapping the color layers). These are sold under brand names such as “Crossbird”, “Lomography”, “Adox Color Implosion” or “Revolog”. These are often smaller editions that are only available on the market for a short time.
Traveling with photographic film
In principle, photographic film should be packaged and kept at moderate temperatures in dark packaging. It is a good idea to package film in resealable plastic bags. If these are kept in your luggage, the film is already safely stowed away.
Particular attention should be paid to air travel. Basically, the silver salts of the photographic emulsion are also sensitive to X-rays - not just visible light.Since checked baggage is X-rayed with quite high doses for air travel, films should never be stowed in your suitcase and checked in. The right place is your hand luggage.
To protect the valuable photographic material the bag with your film should be taken out of your hand luggage. You should ask for a “hand check” by security staff. This is a well-known procedure at airport security checks. It will take a little longer than the standard procedure, so you should allow time for this. Asking for a hand check your film bypasses the X-rays in the hand luggage scanner.
Packing film in metal cans or special lead bags doesn't protect the film from X-rays - the operator at the scanner will simply increases the dose until he has a clear view - so in case of doubt, the film gets more radiation than if it wasn't packaged.
Choosing the “Right” Film
An analog film camera essentially differs from digital cameras in that the light-sensitive “sensor” can be variably replaced. Due to the special characteristics of the photographic material used, the photographer is forced to make some decisions before exposing the film. In the digital world, the visual language and style are created in post-processing; in analogue photography significant determinations are made through the use of the specific photographic film. Therefore, choosing the “right” film is a decisive factor for the finished picture.
To support this selection, it helps to answer certain questions systematically. After a while you will make the right film selection intuitively without conscious thought.
A first, rather mundane question is whether the finished image should be used as a small to medium-sized hand print - up to DIN A4 size - or as a wall-filling enlargement. The latter generally limits select low-sensitivity films with high resolution.
You also need to decide whether the image should be in color or black and white. The actual consideration is whether colors strengthen the message of the image (such as in the image of a colorful weekly market) or whether they can even distract from the actual motif.
Further selection criteria are based on the subject or genre you want to photograph. Typical selection processes are shown below as examples. These are based on the genre, but other starting points for considerations are of course also possible.
People – Should you take studio portraits, or should you photograph people around you? Would colors be distracting – or can they be used? What contrasts and graininess underline the person or scene?
Example: The goal for beauty portraits is fine grain, low contrast and harmonious skin tones. Low-sensitivity black and white negative films with T-crystal technology (e.g. Ilford Delta 100) or low-sensitivity color negative films with natural color reproduction (e.g. Kodak Portra 160) are ideal, especially since artificial light can usually be used.
Landscape – Can a tripod be used or does it have to be taken handheld (e.g. on a hike with little luggage)? At what time of year and day should the pictures be taken? What weather is expected?
Example: If you want to capture the foggy morning atmosphere on a winter hike, the choice would be black and white negative film. Basically, the result should be as fine-grained as possible, which suggests a low-sensitivity film with cubic crystal technology (e.g. Agfa APX 100), as long as there is enough light or a tripod can be used. A compromise for “light” hiking luggage without a tripod would be to use a T-crystal film of medium sensitivity (e.g. Ilford Delta 400). For landscape photos in spring, summer or autumn, colors certainly play a big role. Then you should use a low-sensitivity color negative film (e.g. Kodak Ektar 100).
Street/Travel Photography – Can lighting conditions be predicted while traveling? Are you taking photos at different times of the day? Should buildings and architecture be in the foreground or should more documentary photography be used?
Example: When it comes to street and travel photography, the lighting conditions are certainly not easy to predict. Likewise the time of day the picture was taken. A tripod is usually not used. Medium sensitivity films (ISO 400) would be ideal here. For documentary or architectural images, the classic choice would be a black and white negative film that offers the widest possible exposure latitude (e.g. Ilford HP5+).For photographs of the colorful weekly market, a color negative film would be used (e.g. Kodak Ultramax 400 or Kodak Portra 400).
This list is of course not complete. There are countless photographic situations and creative goals. However, the aim is to show which thoughts and considerations ultimately support the “right” film selection.
This is a list of useful sources on film stock, film types and their characteristics:
Filmtypen - Aktuell verfügbare Filme