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A passenger stands still as a train passes, showing motion blur.

What Does Film Speed Mean?

In the simplest terms, film speed is the measurement of a film’s sensitivity to light. 

Lower film speeds have less sensitivity than higher film speeds. In other words, lower film speeds require more light to create a good exposure. 

Every photo you take is the result of three settings working together – the film speed, aperture, and shutter speed each affect the level of exposure in your final image. 

The goal of any type of photography (but especially important when you’re shooting film) is to perfectly balance all three of these settings.

First things first, it’s usually best to consider what film speed you’re going to be shooting.

Differences Between Film Speeds

So, the difference between film speeds is their sensitivity to light – but what does that mean in practical terms?

In general, lower film speeds are best suited for bright daylight, where higher film speeds are better for situations when you don’t have as much light. 

There’s a large range of film speeds available on the market today – you can find film available in speeds as low as 6 and as high as 3200.

The definitions of a “slow” film speed versus a “fast” speed aren’t set in stone – two photographers might have completely different ideas of what counts as a “slow” film speed. 

Regardless, you can be sure that the lower the film speed, the less light sensitive it will be, and therefore, the more light you will need to get good exposures. 

Aside from helping determine the level of exposure, the film speed has another big impact on the final look of your images.

Black and white film photo of a boys face, the photo exhibits significant grain.

How Does Film Speed Affect Grain?

While faster film speeds cause the film to be more sensitive to light, this sensitivity comes at a price – grain. 

In film photography, grain refers to the very small, random texture that is visible in developed photographs, especially when the photo is enlarged. The photo above is an example of an image with a lot of grain.

So, what exactly does grain have to do with film speed?

Each roll of film has a coating (also known as “emulsion”) that contains a material called silver halide. 

This coating is what enables your camera to record your images onto the roll of film. The reaction between the emulsion and the developing chemicals is what makes images become visible on your negatives once they’re developed.

Silver halide is the component that determines the light sensitivity of a film – the more silver halide, the more sensitive that film will be. 

In film photography, “grain” is really just the amount of visible silver halide crystals.

So, a faster film speed is more sensitive to the light because it has bigger and more frequent silver halide crystals. The downside is that this causes more noticeable grain in the final image.

On the flip side, slower film speeds have much less and smaller silver halide crystals which makes them less sensitive to light but with less noticeable grain. You’ll often see low film speeds claim to have a “fine grain”, meaning it is smoother and more difficult to see.

What is ISO?

If you have any experience with digital photography, you may be familiar with ISO.

ISO, like film speed, is a measure of light sensitivity. But unlike film speed, ISO is a very specific, standardized measurement, determined by the International Organization for Standardization.

Film speed is more of a general term – over time, film speed has been measured using a few different systems (DIN, ASA, and as of 1979, ISO).

Over time, the ISO system remained the standardized measurement. As digital cameras started to be produced, they kept the same system, which is still used today.

What’s the Difference Between Film Speed and ISO?

There’s still a lot of confusion about the differences between film speed and ISO. This is largely because of the switch from ASA to ISO in the late 1970’s.

In reality, there is no difference between film speed and ISO – you can think of them as interchangeable. 

Film speed is a vague term that refers to any measure of light sensitivity, where ISO is a specific term that uses a standardized scale to measure light sensitivity. 

You can think of it like this: ISO is the scale that’s used to measure film speed, but film speed is not a measure of ISO. It doesn’t matter if you’re shooting film or digital photos, ISO is the exact same scale for measuring light sensitivity.

This means that if you’re coming to analog photography from digital, the ISO values from your camera will directly translate to film speeds. 

What About ASA / DIN?

ASA and DIN were two systems for measuring light sensitivity that existed prior to ISO. 

The DIN system was first established in 1934, only measuring black and white film, as that was the only option at the time. The film speed values were presented as degrees ( i.e. 18° DIN) in this system.

Nine years later, the ASA system was created by the American Standards Association. This linear scale for measuring film largely influenced the ISO system when it came out. 

When the ISO system was first established, film speed was presented as a combination of the ASA and DIN systems. For example, 100 speed film would be presented as “ISO 100/21°”.

As time went on, the DIN measurement was dropped from the naming, leaving just the linear scale that originated with the ASA system. 

This means that there is no difference between ISO and ASA. Many people think that ASA strictly refers to film and ISO is only for digital, but this isn’t the case. 

If you have a film that is ASA 400 or 400 ISO, they have the exact same light sensitivity as one another.  

Film photo of the ISO dial of a film camera

How to Choose Which Film Speed to Use

Film speed is usually the first consideration when shooting film photos. While aperture and shutter speed can be adjusted for each individual shot, you’re stuck with one film speed until you finish the entire roll.

Every time you load a fresh roll of film into your camera, you should try to think about the lighting conditions that you plan to shoot photos in. 

With the standard roll of film producing 36 photos, it can be difficult to predict that far in advance, though. 

When we say that film speed is usually the first consideration when shooting photos, a lot of times that means considering what type of film is already loaded in your camera and how to make that work.

As you get more experienced, you’ll find it easier to adjust other settings to make good exposures, even when shooting film that’s faster or slower than you’d prefer. 

If you’re brand new to film photography, we usually recommend sticking with 400 speed film for a little while. A standard speed like this is going to give you plenty of flexibility, especially if it takes you a few sessions to finish shooting a roll of film. 

When to Use Standard Film Speeds

Most analog photographers would consider 400 speed film to be the “standard”.

400 speed film is often the easiest to find and provides the most versatility. You should have no problem shooting ISO 400 film in daylight, later in the evening, or even indoors in artificial light. 

While standard film speeds are versatile, they also produce a relatively fine grain. Generally speaking, most photographers don’t like the look of  grainy photos, so 400 ISO film finds a nice balance between appearance and flexibility. 

In circumstances where we don’t know exactly what we’ll be shooting, nine times out of ten, we’re reaching for a roll of 400 speed film. 

We think of 400 ISO as general purpose film and usually only opt for faster or slower film if the situation specifically calls for it.

When to Use Fast Film Speeds

There are some circumstances where 400 speed film just won’t cut it – night photography, concerts, and anything requiring a fast shutter speed can all be tough to shoot with 400 ISO film.

Even the jump from ISO 400 to ISO 800 gives you a bit more wiggle room, but the increase in grain can be quite noticeable. When you start getting into the super high-speed films (around 1600 – 3200 ISO), the grain becomes pretty significant. 

That said, most people would prefer a good exposure with some noticeable grain over a photo that is way too dark.

If you don’t have much available light and need to use a faster film speed, don’t be too worried about your photos being too grainy. Instead, just do whatever you can to get good exposures – even if that means using a tripod or a wider aperture. Underexposed images are where excessive grain can really ruin a good shot.

It’s also worth noting that for color film, it’s almost impossible to find film rated 800 ISO or faster. Black and white has a lot more options, and generally speaking, people don’t seem to mind the grain as much with B&W film.

A grainy film photo of a dog
This photo was taken on 1600 speed film.

Black and white film photo of clouds, showing a lot of grain.
This photo was taken on 3200 speed film.

When to Use Slow Film Speeds

Films slower than 400 ISO are usually best suited for very bright outdoor conditions. 

While it can be a bit difficult to shoot slower film speeds, the quality makes it worth the challenge. Especially with film rated 100 ISO or slower, the grain is incredibly fine, producing super smooth, sharp images. 

This becomes even more relevant as you print images at larger sizes. Even a standard, 400 speed film is going to show more grain when it’s blown up larger than 8×10 inches. 

This is why slow film stocks are often the choice of landscape photographers – they want the most detail and the least amount of grain possible. 

Landscape photographers commonly utilize tripods and slow shutter speeds, so a slower film speed is not as daunting. By using a tripod, you eliminate the issue of camera shake and can achieve the correct level of brightness just by adjusting the shutter speed. 

Film photo of surfers riding a wave as the sun sets behind them.
This photo was taken on 100 speed film.

Film photo of a small stone building on the side of a mountain.
This photo was taken on 100 speed film.

How to Change the Film Speed on Your Camera

The method to change the film speed depends greatly on what type of film camera you’re using. Some cameras, especially film point and shoots, don’t even allow you to change the film speed manually. 

Manual film cameras usually have some sort of dial to change film speed, often located on the top of the camera in the same place you’d change the shutter speed. 

If your film camera is electronically controlled and has some sort of screen to adjust settings, chances are that this is how you’ll change the film speed. 

Since the method will be different for each and every camera, the only universal way to change the film speed is to check the user manual. We’re big fans of for finding free online user manuals for vintage film cameras.

DX Encoding

Cameras are able to automatically set the film speed because of a system called DX Encoding. 

Established in 1983, the DX code is a barcode and additional marking on 35mm film canisters that tells the camera the film speed, number of exposures, and exposure tolerance.

Most film cameras produced in the mid-1980’s or later are able to read DX codes. This system only applies to 35mm film, although DX codes were also included on APS film before it was discontinued. 

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