Publishers of technology books, eBooks, and videos for creative people

Home > Articles > Digital Photography

This chapter is from the book

1. Fast vs. Slow Lenses

Within all Canon lenses, there is something called the aperture. More specifically, the mechanism that makes up the aperture is the diaphragm, a ring of overlapping, thin metal plates that either close down or remain open during exposure. For the sake of clarity, we refer to this mechanism as the aperture.

The aperture controls two things: how much light is let in through the lens and exposed on the sensor (or film), and depth of field, or how much of the shot is in focus. We’ll discuss these two points in the next chapter.

Lenses are often described as either fast or slow, based on their maximum aperture openings. When making an exposure in any given light condition, the larger, or more open, the aperture is, the faster the shutter speed needs to be. When you allow a large amount of light to pass through the lens, you need to cut it off more quickly for a proper exposure. Conversely, an aperture that is closed, or stopped down in that same light condition requires a slower shutter speed to create the exact same exposure (Figures 1.1 and 1.2). Essentially, faster lenses are those with large maximum apertures, and those that cannot open up as much are referred to as slower lenses.

Figure 1.1

Figure 1.1 At f/2.8, the lens’s aperture is considered fast since it allows much more light in at one time than a slower aperture value, such as f/5.6 (see Figure 1.2).

ISO 200 • 1/1000 sec. • f/2.8 • 46mm

Figure 1.2

Figure 1.2 An aperture value of f/5.6 is two stops slower than f/2.8, meaning the shutter speed used in this shot is two stops slower than the speed used in Figure 1.1.

ISO 200 • 1/250 sec. • f/5.6 • 46mm

Canon makes several variations on many of their lenses, and much of the variance between them is aperture based. For example, there are three different 50mm lenses in the Canon lineup: the flagship 50mm f/1.2L, the 50mm f/1.4, and the 50mm f/1.8 (also known as the “nifty fifty”). The number following the f-stop is used to identify the maximum aperture opening—the lower the number, the larger the opening.

The 50mm f/1.2L is the fastest of the 50s, and the 50 f/1.8 is the slowest. Practically speaking, the 50mm f/1.2L—at its maximum aperture—lets in more light and allows the shooter to use faster shutter speeds than the other two 50s allow. This comes in handy when shooting in low-light conditions (Figure 1.3). As we’ll discuss later, faster lenses are also valuable on the sports field.

Figure 1.3

Figure 1.3 Shooting live music requires a fast aperture to freeze the action and handhold longer lenses, even if the shot is a tight headshot of a keyboard player.

ISO 2000 • 1/320 sec. • f/2.8 • 93mm

These three lenses are non-zoom lenses (also known as prime lenses, covered later in this chapter). Canon also manufactures many great zoom lenses, and in doing so, introduces another issue—lens speed. Some lenses, such as the 24–70mm L and the 70–200mm L have a fixed f/2.8 maximum aperture opening. However, other lenses, such as the 18–55mm f/3.5–5.6 and the 70–300mm f/4–5.6, have what is commonly known as variable maximum apertures. Simply put, lenses with variable maximum apertures will close down their maximum aperture as they are zoomed in to the scene. For example, when shooting with an 18–55mm f/3.5–5.6 lens at 18mm—the widest focal length on that lens—the maximum aperture is f/3.5. When zoomed in to 55mm, though, the maximum aperture changes to f/5.6. Along the zoom range, as the focal length increases, the maximum aperture changes to a slower aperture.

These types of lenses are fairly common, and the variable maximum aperture is a result of using smaller-diameter lens elements in the lens, which subsequently keeps costs down. It’s worth noting here that the faster the lens, the more expensive it is. It takes more materials to manufacture faster lenses—more glass, more housing for that glass—since the diameter of the lenses are larger. Oftentimes, the fastest lenses are reserved for the L series. These lenses are made with premium materials, glass being just one of them (more on this subject later in this chapter as well).

Lens speed also refers to how a lens handles depth of field, so keep in mind that the faster the lens, the more one can theoretically throw the background (and foreground for that matter) out of focus. Consider again the 50mm example above. The 50mm f/1.2L, while set at f/1.2, will produce a softer bokeh (the area of the image that goes out of focus when using a faster aperture) than the 50mm f/1.4 and f/1.8 (Figure 1.4). It might be a stretch to see the difference between f/1.2 and f/1.4, but it is there. A more extreme example is the difference between the iconic sports lens, the 400mm f/2.8L, and the nimble-yet-razor-sharp 400mm f/5.6L. There is a considerable difference between the lowest amounts of depth of field each produces when set to maximum aperture.

Figure 1.4

Figure 1.4 An aperture lower than f/2.8 offers a unique way of isolating portrait subjects from otherwise distracting backgrounds. At f/1.2, there is only a sliver of carpenter Jason Duby in focus, while the rest of the foreground and background soften drastically.

ISO 50 • 1/200 sec. • f/1.2 • 50mm

Peachpit Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Peachpit and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Peachpit products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive:

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020