Smartphones have largely replaced cameras, and for many occasions they are as good as or better than our old pocket film cameras.

Smartphone cameras began to rival good pocket cameras with the arrival of the iPhone 4s in 2011, which rivaled the Canon PowerShot S95 in reviews of picture quality. CNET called the camera “brilliant” in their October 2011 review. The 8-megapixel camera captured images that exceeded the requirements for good 4-by-6-inch prints.

It wasn’t long before people stopped carrying Nikon, Canon, and other digital pocket cameras, replacing these with smartphones.

Apple bought LinX Imaging in 2015 for $20 million. The LinX camera system uses multiple extremely small lenses, in pairs or sets of four, to capture high-resolution images that can be modified by software later. LinX also designed small cameras capable of capturing 3D images for virtual reality.

In a few years, the iPhone line will feature cameras as good as large-body “fixed-lens” cameras with optical zoom and manual settings.

The 2016 iPhone 7 and 7 Plus have the ability to capture 12-megapixel images equivalent to a 28mm lens on a 2006 Canon 30D DSLR camera, which featured an 8.2-megapixel sensor and sold for $1,500. The 7 Plus adds a second lens equivalent to a 55mm lens on the 30D. This second lens offers a “telephoto” mode on the iPhone 7 Plus with a true optical zoom instead of digitally cropping the image. Most high-end smartphones offer similar, or even better cameras.

If smartphones can capture good images, why would you want a dedicated camera?

For hobbyists and professionals, the ability to change lenses, add physical filters, and control settings remain important.

Would you trust a wedding photographer using a smartphone? Probably not, and for good reason. Several factors affect the image quality of a digital camera including sensor size, megapixels captured, image signal processor, and physical optics. A smartphone is not a professional-grade camera.

Vendors of digital single-lens reflex cameras (DSLR) and mirrorless cameras know that today’s camera shopper has a smartphone. The DSLR and mirrorless cameras have to be better, a lot better, to compete.

A DSLR is something of a holdover from the past. A hinged mirror inside the camera reflects the image from the lens through the viewfinder. Some digital cameras maintain this system to accommodate film camera lenses. I know photographers who collect “classic glass” because some lenses from the 1960s and 70s are considered the best ever made.

Without question, the king of DSLR is Canon. Yes, there are Nikon enthusiasts with massive collections of Nikkor lenses, and the cameras are great. But Canon’s top-tier models dominate professional photography, according to statistics on Shutterstock and Getty Images. The Canon 5D and 1D lines are the best-selling DSLR camera bodies. The Canon 5Ds features a 50.3-megapixel sensor measuring 36-by-24mm. The 5Ds retails for $2,500, without a lens.

Enthusiasts often like the affordable and flexible 7D, which uses SD cards to store images. The 7D has a smaller sensor, based on the Advanced Photo System (APS) film size from pocket film cameras. The 7D retails for $1,300, and online retailers often include two lenses.

The DSLR was a good idea in the days of film: you saw exactly what the film would capture. But, with electronic viewfinders and large screens on cameras, the mirror and its complex mechanisms add weight and bulk to the camera.

The best mirrorless cameras, according to PC Magazine and Digital Photography (dpreview.com), are from Leica, Panasonic, Sony, Fujifilm, and Olympus. Canon’s EOS M3 is also a mirrorless camera. The Olympus OM-D line receives the highest ratings for still photography, including the best user reviews.

The Olympus and Panasonic cameras feature a smaller sensor, known as Micro Four Thirds (MFT), that happens to be the same size as many 35mm cinema film. I own a Panasonic GH4 and use it for video production. The new Panasonic GH5 promises even better images and video, incorporating technology developed with Leica.

Smartphone cameras must feature, out of necessity, small sensors with minimal optics. The camera in your phone is the result of many compromises to make it fit in a small corner of the device.

Comparisons between a 12-megapixel phone camera and 8.2-megapixel Canon 30D are made because the larger APS-C sensor and full-frame lens combine for better light sensitivity and overall optical quality. A new smartphone captures images as good as a mid-range digital camera body from ten years ago with a single lens.

Smartphones use sensors that are less than a third of an inch, measured diagonally. The smaller a sensor, the less light it captures. If you take photos in low-light conditions, the larger the sensor the better its light sensitivity. The Canon 30D sensor is 20 times the size of an iPhone’s sensor. A full-frame digital camera, with a sensor the size of 35mm film, features a sensor that is 50 times the size of a most phone camera sensors.

Each “pixel” in a camera sensor is actually a square of four photosites, sensitive cells that respond to color and brightness. To cram 12 megapixels (4000-by-3000 pixels) into a third of an inch, the photosites must be microscopic. The light hitting one pixel hits many nearby pixels.

The larger sensor of a dedicated camera allows for both larger pixels and more space between pixels. This results in cameras with sensors capable of extreme speed in bright light and impressive low-light capabilities.

All those pixels captured by an image sensor are interpreted and stored as data. The image signal processor, a specialized computer chip, works to improve the final photograph based on the data from the camera sensor.

Regardless of the quality of a sensor and the power of the image signal processor inside a phone or camera, the physical optics capturing the light and focusing it on the sensor determine how sharp a photographic image can be. A good lens matters at least as much as a good sensor.

You cannot compare a high-end digital camera lens to the lens on the back of a smartphone. A great lens can cost thousands of dollars for good reason: it is a precision instrument. But, Apple intends to challenge digital cameras. The competition is exciting.

About the Author: Visalia native Scott Wyatt is currently completing his Master of Fine Arts in Film and Digital Technology at Chatham University, in Pittsburgh, Pennsylvania. Scott has several additional graduate degrees and was a visiting professor of business communication at Carnegie Mellon University.