What Does Lens Speed Mean In Photography? Fast Lens v/s Slow Lenses


Thinking of which Dslr camera lens to buy? Or what does lens speed mean? Then don’t worry here all your doubts would clear.

Photography is not so easy. One needs to invest much time and patience to learn every aspect of it.

Before proceeding to this amazing professional career one needs to understand the cameras, lenses, and so on. Apart from that visualization is also a great factor. It is because when you want to shoot in different conditions you need a different mindset.

Maybe you have a perfect camera and also have a kit lens and want to buy a DSLR lens. Before buying a DSLR camera lens you have to choose carefully which lens is right for you.

The DSLR lens largely depends on

  1. Type of dslr lens
  2. Type of photography
  3. The existing experience you have

Suppose you are a beginner then your lens requirement would be different. For an amateur the lens is different and for the professionals the lens requirement is also different.

Whether to buy a fast or slow lens?

Here in this article, you can explore the fast lens and slow lens in detail and typically what lens speed mean in the world of photography.

Fast Dslr Lens and its uses

Now, what is the fast lens? How does it work? What are the uses of fast Dslr camera lenses or when can they be used? Do I need a fast lens? So all this will be cleared up in this section…

The fast lens in photography means a lens that has a smaller aperture number is called the first lens. The aperture is denoted by the “f” number. So f/1.2, f/2 lenses are called fast lenses.

This smaller number signifies that the lenses have a larger aperture opening. The fastest lenses have the shortest exposure. Apart from that fast Lens also depends on a variety of factors which we have explained below.

Talking about uses, fast lenses can be used in portrait photography, sports photography, etc.

Now you know what fast lens speed means in photography. So, let’s move on to slow lenses…

Slow Camera lens and its uses

After understanding fast lenses, you must be thinking now what is the definition of a slow lens or when a slow lens can be used?

So, slow lenses in photography are the lenses that have generally smaller aperture openings. Thus have a larger aperture number. Slow lenses are generally used for longer exposure. Any lens having the f-number beyond f/4 is considered as the slow lens.

Talking about its uses, they are more often used in landscape photography.

Difference between fast and slow lenses| Fast Lenses v/s Slow Lenses

After a short definition to slow lenses and fast lenses, let’s know the actual difference between them.

Fast lenses are the lenses that can be described along with the aperture. A usually larger aperture is the main characteristic of fast lenses.

In Layman’s understanding, we can say that the lens has a larger aperture considered as the fast Lens. The larger aperture refers to the large opening of the lens.

If we try to understand the concept of the fast lens and slow lens then we have to deal with the lens speed.

Let’s understand what lens speed mean.

The Lens speed involves the relation between f/stop, ISO, and shutter speed. The f/stop, ISO, and shutter speed are completely dependent on each other. These three factors are considered as the exposure triangle in photography terminology.

To know each factor correctly, let’s understand f/stop first. Do you know how f/stop gets calculated?

F/stop is the distance between the focal point and sensor. The focal point generally lies somewhere between the optical elements present inside the Lens barrel.


          F/stop = focal length ÷            diameter of the aperture

Suppose you have a lens having a focal length of 50mm and a diameter of the aperture of 25mm. Then the f/stop would be f/2.

If you have a lens that has a higher aperture then you can use a higher shutter speed while taking shots. The larger aperture means more light entering the sensor. Setting a higher shutter speed signifies that you are actually cutting the amount of light hitting the sensor. Here you don’t need any longer exposure.

To understand the concept let’s take an example.

Suppose you have two lenses that have aperture f/2.8 and f/4 respectively. If you can use 1/2000s shutter speed in f/4 lens to get a perfect picture then in f/2.8 you can double the shutter speed up to 1/2000s. That means in high aperture lenses you can use high shutter speed. In the f/2.8 lens, you are cutting the amount of light in half to reach the sensor using shutter speed.

In general, we can understand the f/2.8 lens is much faster as compared to the f/4 lens. If you want the best pictures in f/4 lens just like f/2.8 lens then you have to raise your ISO. Here is why the exposure triangle involves which we have discussed. So faster lenses have higher opening and smaller aperture values.

Talking about the bokeh effect of first lenses, fast lenses can give you an exceptional blurry background. That means there is a connection between aperture and blur effect.

As fast lenses can work better in low light, these lenses can give you a shallow depth of field. As a result, you can separate the subject from its background and can achieve a maximum blur effect. That clearly helps portrait photography as well.

Though faster lenses can give you amazing blur effect drawbacks are there too. The faster lenses can sometimes give the entire picture out of focus.

For example, suppose you want to take a picture of a person carrying a football. If you want to focus on football then you can get the person’s face out of focus and vice versa. Of course, there you can get a blurry background but things would be complicated when you want to shoot entire pictures in one frame.

Further depth of field also largely depends upon the focal length as well. If you have a smaller focal length then you will get a larger focus and greater depth of field that certainly helps to achieve blurry background. So super wide-angle Lenses can produce a better depth of field than telephoto lenses. As you zoom in the depth of field decreases at the telephoto end.

As you come closer to the subject the depth of field also gets affected. In close shots, you can get less depth of field and blurrier background.

So in faster lenses, a blurry background mainly depends on the depth of field, f/stop, distance to the subject, and focal length.

There are many lenses Canon has produced over the years. Talking about the Canon primes, Canon 50mm f/1.2 and Canon 50mm f/1.8 of which 50mm f/1.2 is much faster as compared to the 50mm f/1.8. It is because the f/1.2 has larger openings and there you can use a high shutter speed that certainly benefits the low lighting conditions.

When it comes to zoom lenses, brands like Canon, Nikon, Sony, etc. have produced so many great fast zoom lenses. In all their zoom lenses they all introduce lens speed as well.

For example, talking about a Canon fast lens i.e. 24-70mm and 70-200mm (from L-series) , these two have fixed focal lengths of f/2.8 throughout our zoom range. That means the lens is faster in all focal lengths.

Then what about the zoom lenses that have variable aperture?

Talking about Canon 18-55mm f/3.5-f/5.6 and 70-300mm f/4-f/5.6, In 18-55mm as you zoom in the opening of the aperture decreases means at 55mm you have the aperture of f/5.6 but at 18mm you will get the aperture of f/3.5. So these lenses can behave slower or faster at the different focal lengths.

In variable aperture lenses, the diameter of the aperture is very less. That means the optical elements have less diameter which conveys that slow lenses are cheaper compared to fast lenses in photography.

But in the case of fast lenses, there is more housing of large diameter and special elements that Canon has exclusively preserved for their L-series lenses which makes the faster lenses quite expensive. Thanks to some of the cheaper fast lens of Canon i.e. Canon 50mm f/1.8 lens is a great low-budget fast lens.

Talking about the slow lenses in slow lenses the aperture opening is very small. So here you need a longer exposure and lower shutter speed. The slow lenses are designed for long-distance photography.


Depending upon the need you can choose a fast lens or a slow lens. Choosing a fast lens on a budget is a bit difficult. However, Canon has also produced some of the fast lenses which you can go for.

Slow lenses are generally cheaper and you can also go for that but here you have to be careful about the light availability as well. So, I hope your doubts or your questions about slow and fast lenses and what lens speed mean photography, are very much cleared up through this article. If there is anything else you won’t ask, do not hesitate to contact us.

Frequently Asked Questions

Q. Is 2.8A fast Lens?

A: Yeah, 2.8A is a pretty good fast Lens that can allow you to shoot in low light as well.

Q. Which f/stop is sharpest?

A: The Lens has f/1.2 is considered as the very sharpest lens.

Q. Is a 1.4 or 1.8 lens better?

A: The 1.4 lens is slightly faster than the 1.8 lenses. However, both are fast lenses which are good which you can go for.

Q. What does the f/1.4 mean?

A: f/1.4 suggests that the lens has a high aperture opening which can draw maximum light inside. You can use high shutter speed while using this. The f/1.4 lens can work better in low light too.

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