The Sweet Spot of a Lens

Sweet spot of a lens

To understand the sweet spot of a lens, we need to look into the math of f stops. Don’t worry. It’s not that bad and once you get the basic idea, you will be able to apply this knowledge in many situations.

F stop is the measure of how much light can pass through a lens. The smaller the number, the wider the hole and the more light that can pass through. F stops are a ratio of focal length (distance of the focal plane to the lens,) divided by the diameter of the lens aperture. Because it is a ratio, it is always written as a fraction – f divided by a stop number like f/2 or f/4. By doubling the diameter of the stop number from f/4 to f/2, you get 4 times as much light striking the sensor.

Make a list of doubling numbers: 1, 2, 4, 8, 16, 32, 64, 128. Now take the square root of each. You get 1, 1.4, 2, 2.8, 4, 5.6, 8, 11 (11 is 5.6 doubled and rounded off) This is the standard f/stop scale. It’s a geometric sequence. Each stop on the scale represents half as much light. So a lens that is rated f 1.4 allows in twice as much light as a lens that’s rated f/2. That’s 8 times as much light as an f/4 lens.

Here’s a trick to remember the f/stop scale. Just remember f/1 and f/1.4. With these you can find all the rest by simply doubling the numbers.

2 times 1 is 2.
2 times 1.4 is 2.8.
2 times 2 is 4.
2 times 2.8 is 5.6.
2 times 4 is 8.
2 times 5.6 is 11 which is rounded off.

Kinda cool, huh?

The Sweet Spot of a Lens

The sweet spot of a lens is the sharpest aperture setting. While each lens is different, the general rule of thumb is that you get the sharpest point by stopping the aperture down 2.5 to 3-stops from the lens’s maximum aperture. So if the maximum aperture of your lens is f/2.8, you’ll want to shoot with your lens aperture set between f/5.6 and f/8 from the widest opening.

If your lens is an f/1.4, meaning its widest aperture is f/1.4, then the sweet spot of your lens is somewhere between f/2.8 and f/4.

This sweet spot of a lens is not the same as depth of field. When you stop a lens down to smaller apertures, more of the image is in focus. Stopping a lens down to smaller apertures does not the increase the focus equally fore and aft of your subject, but rather 1/3 in front of the subject and 2/3 behind.

But what many shooters don’t realize is that you will also get softer images with the aperture at its smallest opening. This is caused by diffraction where the light rays are bent slightly as they pass through a very small aperture. So beyond a certain aperture the images are increasingly less sharp. That’s the trade-off to using smaller apertures to achieve a greater depth of field. At some point the aperture size will cause some softening which is caused by diffraction.


Keep Reading...

google earth

Google Earth Gets Major Update

Before you check out the new Google Earth, make sure you are first running Google Chrome on your desktop or Android on your phone. iOS will be available soon. Last year Google released a VR version of Google Earth. This new version is no longer a separate app, but a web site https://www.google.com/earth/ . This […]

Read More
Produce Business Videos

Professional Video Producer: How To Start a Successful Video Production Business

Start part-time or full-time in this lucrative and satisfying work. Earn the respect of small businesses, corporations and non-profits who rely on your expertise. This is an amazing adventure and the best way to pay for video equipment!

Read More
The White Helmets

Oscar-Winning Documentary The White Helmets

Khaled Khatib working on the Oscar-winning documentary short “The White Helmets.” “The White Helmets” tells the story of a group of civilian volunteers in Aleppo who search for and rescue bombing victims. The White Helmets often claw out the rubble with their bare hands. They have saved over 78,000 people who were buried from the […]

Read More

Home Movies Day

If you are transferring home movies (either film or video) as a commercial service, you should know about the non-profit Center For Home Movies . They sponsor Home Movie Day which will be on October 17, 2015. The site also will show you some possibilities you may not have considered. For instance numerous feature-length documentaries […]

Read More


Leave a Reply

Your email address will not be published. Required fields are marked *


  • Forbes Magazine calls VideoUniversity one of the best business-to-business sites for digital video production.
  • WINNER
    Videography Magazine's
    "Website of the Month" Award
  • WINNER
    PC Magazine Online "Best Desktop Video Site" Award
  • WINNER
    CyberFilm School's "FOUR STAR" Award