What is an f/stop really?
January 10, 2022A film camera is a film-based device with film’s ISO setting determining the film speed. The aperture of the film camera also needs to be taken into consideration when working with photography because it directly affects how much light will hit the film, thus affecting the film exposure.
Apertures are expressed as f/stop values. The bigger the film exposure, the more light enters the film camera, resulting in brighter photos.
When working with film camera aperture it is important to know that changing one nominal f/stop setting on an enlarged, will change film exposure by nearly half of a stop. For example, if you are photographing on ISO 100 film and set the aperture to f/8.0, then you need to compensate for this by setting shutter speed or film iso accordingly (to either 1/15s or 200 respectively).
So what is an f/stop, really?
To explain f/stop, it is best to start with the film aperture. The film aperture is a hole that opens up when you take a photo. If you are using a big aperture (small f/stop value) more light will get onto the film surface thus making film exposure lighter. Conversely, if you are using a small film aperture, less light will hit the film surface and film exposure will be darker.
The f/stop number goes hand in hand with film exposure because it determines how big or small film aperture is going to be. The sequence of film camera aperture f/stops starts from wide-open film aperture (largest opening), which has a value of 1.0, then increasing film camera aperture f/stops up to 22 (the smallest opening) with each value being a double aperture size in relation to its predecessor.
For example, film camera aperture 1.4 has a film exposure area that’s twice as big as aperture 1.0, and film exposure 2.0 is twice film camera aperture 1.4 film exposure area, so on and so forth.
One more thing that I would like to mention in regards to film camera aperture is film speed which also needs to be considered when working with film. Film speed is rated in film exposure numbers (or film ISO) and it is rarely the same as film camera aperture numbers, so you need to keep this in mind when doing film photography because these two values determine how much light gets on the film surface during film exposure.
Aperture-priority mode is also known as Av or A mode. This aperture setting allows you to choose film exposure by selecting the aperture while the film camera automatically sets the corresponding film speed. For example, if you are using ISO 100 film and set film exposure to f/8.0 then it will be correct since this is ISO 100 film camera aperture value for medium grey tone.
The main reason film photographers use aperture-priority film camera mode is because they can control the depth of field by manipulating film camera aperture.
For example, if you want to make film exposure look like it’s taken at night (to isolate the main subject against dark surroundings) then you need to set film exposure to a larger aperture number value which will increase film exposure and make the film look like it was taken at night.
On the other hand, if you want to take a photo of a landscape with film camera aperture being as large as possible you need to set film exposure on a smaller aperture number which will decrease film exposure making the film look like it’s bright outside.
It is also worth mentioning that film camera aperture can be adjusted in both film cameras and digital cameras, but the ways these cameras implement film camera aperture changes are different.
For film cameras, you can choose aperture manually or use a light meter to measure the exposure which will give you the aperture value that is required for film exposure to be correct.
On the other hand, some cameras use aperture priority mode where they automatically choose f/stop based on film speed and brightness of the scene.
Film photography can be a very rewarding hobby/profession if you know how film and camera aperture works. Now that you know the basics of aperture term, try taking some photos and see what can do for you!
Until next time enjoy some shots below…
