The aperture is one of the primary sources of consternation for most photographers. It’s bad enough that we have to compute shutter speed/aperture ratios, but understanding the mathematical principals behind an aperture and how it works is like decoding hieroglyphics to any beginner. I’m here to break it down for you, to the best of my ability. However, I’m not much of a math wizard, so I called upon seasoned photographer Matt Cole, who published a webpage about apertures back in 2002 called “A Tedious Explanation of the F/Stop.” To this day, Matt’s page is the most helpful reference I could find regarding aperture and other photographic skills. He was even kind enough to impart some of his genius to me over the phone. Be sure to check it out for a more in-depth look.
The aperture is made up of a set of expandable and contractable metal blades in the camera’s lens that form a hole. This hole is responsible for letting light onto the camera’s sensor. Opening that hole up wide lets the most amount of light onto the sensor while closing the hole down lets the least amount of light onto the sensor.
Diagram of an 8-Bladed Aperture
The opening of the aperture’s hole is measured by F/Stops. As shown above, F/Stops are usually displayed on a camera’s lens and increase in value. According to this particular lens, at F/3.5, the aperture is opened up to its widest hole while at F/32, the aperture will be closed down to the smallest possible hole. Why is it that the larger the number, the smaller the hole?
It’s because F/Stops are a ratio of two things: the diameter of the aperture in the lens and the focal length of the lens. For instance, if we had a lens at a 135mm focal length, adjusting the aperture to F/3.5 would mean the aperture (hole) is open 38.6mm (135/3.5 = 38.6). A 135mm lens at F/22 would mean that the aperture is open 6.1mm (135/22 = 6.1). Therefore, the higher the F/Stop (aperture value) the smaller the hole, while the lower the F/Stop the wider the hole.
Traditional apertures double or halve the light. As an example, F/2.0 is twice as bright as F/2.8. F/11 is twice as bright as F/16. The following sequence is the standard for aperture values:
F/1.4 F/ 2.0 F/ 2.8 F/ 4 F/ 5.6 F/ 8 F/ 11 F/ 16 F/ 22
As you look at the above F/Stop sequence, think wide –> narrow. An F/1.4 lens is regarded as a very bright or fast lens while an F/22 lens is regarded as a slow lens. The aperture ratio sequence is the same as the shutter speed sequence. Shutter speeds double and halve in stops, allowing twice the amount of light in or cutting twice the amount of light in half.
The aperture is the size of the hole that light passes through to hit the sensor. The shutter speed is the amount of time the aperture stays open.
Here’s a standard shutter speed sequence:
8 seconds 4 seconds 2 seconds 1 second 1/2 second
1/4 1/8 1/15 1/30 1/60 1/125 1/250 1/500 1/1000
There’s a caveat here. Fast (bright) lenses let lots of light into the shot and let us shoot at faster shutter speeds to minimize blur. For instance, on my Canon PowerShot S100, I can set the aperture to F/2.0 and the shutter speed to 1/100 in a typical shooting environment. If I then set the aperture to F/8.0, I’d have to adjust the shutter speed to 1/8 to compensate for the aperture’s smaller hole, which is letting less light in. This basically means that the shutter is open longer to let more light in rather than the aperture being opened wider to let more light in. The shutter speed/aperture team is a ratio.
And now for the caveat: Depth of Field. It’s great that an F/2.0 lens will let the light come pouring in and allow you to shoot at faster shutter speeds to avoid image blur. But that comes at a price. Traditionally, the F/2.0 lens has a shallow depth of field, meaning the lens will only be able to focus on objects in the foreground or background, but not everything at once. Many portrait shots are captured with bright lenses because the background does not have to be in focus, and the blurred background even adds an artistic effect to the image.
Here’s an image I took at F/3.5 with the Pentax K-7, focusing in the middle of the flower while the pedals of the flower in the foreground and bee in the background are out of focus:
As you can see, only the center of the flower is focused. Here’s a shot taken with the Pentax K-2000 at a much more narrow aperture, somewhere in the F/22 range:
In the second shot, everything is in focus, from the rocks on the shore to the farthest building behind the Brooklyn Bridge. Although it helped that I was farther away from my subject, the F/22 aperture ensured me that everything would be in focus. If I had used a much narrower aperture, say around F/22 with the picture of the flower, everything would be in focus, from the pedals to the bee.
But there’s another caveat here as well. Depth of field all depends on the size of the camera’s sensor and your distance from the subject, in addition to the camera’s aperture. One thing you’ll notice on a typical point-and-shoot is that it has a small aperture range. Most only go up to F/8. This is because the aperture in a point-and-shoot camera is tiny compared to that of a DSLR lens, and it would be too difficult for manufacturers to achieve such a small hole with such a small aperture configuration. However, most point-and-shoots have a fantastic depth-of-field because of the smaller camera sensors and shorter lenses. As a general rule, shorter focal lengths have greater depths of field.
We’ll get into depth-of-field and focusing in another edition at a later date, but be sure to leave any questions, comments or concerns in the comment section. For more in-depth explanations, be sure to visit Matt’s page at http://www.uscoles.com.
The Galaxy S20 Ultra's Space Zoom camera is amazing and a bit creepy
The Galaxy S20 Ultra supports up to 100X zoom, which Samsung calls Space Zoom, but is it any good? Can a phone really product usable photos at 100x zoom? We've got our Galaxy S20 Ultra already so join us to find out!
Win an iPhone, iPad and Apple Watch with the Reader's Choice giveaway!
What's the best phone of 2019? Is it the iPhone 11 Pro, Pixel 4 or OnePlus 7T? What about the best laptop, games console, tablet and more? Vote NOW in the Reader's Choice awards and win BIG in time for the holidays!
Here are the best products from IFA 2019!
Here are the products announced at IFA 2019 that were worthy of our Best of IFA 2019 awards. Also featuring MrMobile's single best product at the show!
Best large format printers for stunning professional-quality prints
Even with similar underlying technology as large format printers, standard desktop printers are not capable of handling large documents. The beauty of large format printers is that they have regular or smaller papers which gives you the freedom to scale up or down when printing. Whether you a seasoned printer looking to size up or a beginner, our list of the best large format printers...