13th Blog Post, First Published on August 28, 2016, as a Newspaper Column.
(Photos and possibly an extended text will be added soon).
Hi, and welcome to my “HighLight & Shadow” photo Blog.
Today’s post is the second of two-posts that looks closely at how optical and digital zooms differ from each other.
The photographic term “zoom” refers to enlarging or shrinking the image of a scene projected into a camera, without changing camera lenses or changing the camera’s position in relation to that scene. Understanding the differences about these two methods of zooming will help you when looking to purchase a new camera phone or point-n-shoot camera and when using many different digital cameras.
All digital cameras create photographs by projecting images of any scene through the lens and its aperture, into the camera body and onto a light-sensitive digital sensor. (An aperture is the adjustable opening inside lenses to precisely control the amount of light that can shine through the lens at any given moment). The projected scene actually extends past the four edges of the sensor, but the camera only records the area of the scene that is projected onto the camera’s sensor.
Let’s start with a few basics of how zoom lenses work and how that relates to optical zoom and digital cameras. Then we’ll compare the quality of photographs shot using optical zoom verses digital “zoom” on two imaginary digital cameras, and lastly, we’ll scrutinize the photos accompanying this post taken with optical zoom using my small point-n-shoot camera and with digital “zoom” using my camera phone.
Zoom Lenses and Optical Zoom
Zoom lenses are many lenses in one lens, allowing photographers to adjust their zoom lens instead of physically changing lenses, to vary the scenes’ magnification. Zoom lenses change magnification by shifting some of the lens elements inside the lens, forwards or backwards, producing an infinite variety of magnifications, from the lens’ widest angle of view to their most narrow (or telephoto) angle of view. Zooming in magnifies the image in the camera and zooming out shrinks it.
When shifting from a wide angle to a more telephoto angle of view, everything being projected onto the digital sensor grows larger, forcing the outer parts of the image to extend beyond the sensor’s frame and cropped out of the image, thus magnifying the image on the sensor. AND, with optical zoom, the camera records every image using 100 percent of the sensor’s pixels, no matter what angle of view the lens is set at, thus maintaining a consistent image size and image quality at all of the lens’ magnification settings. This is similar to the consistent image size and quality produced in the camera when changing between a wide-angle lens and then a telephoto lens, but with optical zoom, we simply zoom the lens to change our angle of view almost instantaneously.
Cameras with digital “zoom,” on the other hand, magnify the scene as well, but far differently and with very different results in image quality. Most cameras with digital “zoom” do not have optical zoom, so the lens itself doesn’t, and can’t, magnify the scene. Instead, its lens continues to project the same magnification of any scene, all the time, so the only way the camera can “zoom in” is to reduce the area of the sensor used in capturing its photographs. Smaller and smaller areas of the sensor’s surface record the images as we “zoom in” to a scene. Digital “zoom” is achieved simply by cropping the full image itself ; by using less and less of that image to create the sense of magnification. Consequently, as we increase the scene’s magnification using digital “zoom,” our images degrade more and more.
Two Imaginary Cameras
To help illustrate these differences, lets pretend we have two 12-megapixel digital cameras from the same manufacturer. Both cameras record photos using identical digital sensors of approximately 12 million pixels per sensor. However, one camera has optical zoom capabilities and the other only has digital “zoom” capabilities. We’ll pretend to shoot four photos of the same scene with both cameras, first with both camera’s widest-angle setting and then shooting three more photos further magnifying the scene equally in both cameras, ending with the most telephoto setting.
Our optical zoom camera uses its lens to enlarge the image projected onto the digital sensor, so every photo is recorded by all of the sensor’s 12 million pixels, no matter how magnified the image is.
The digital zoom camera’s lens has a fixed focal length lens so it’s unable to change its angle of view, so it has no zooming capabilities what-so-ever. The only way it can zoom is by cropping the image projected onto the sensor which means using fewer and fewer of the sensor’s 12 million pixels as it magnifies the scene, thus reducing its image quality more and more as the camera “zooms in” further and further.
Using digital zoom is no different than if we shoot a photo and later decide that we want to make part of the photo larger, so we crop parts of the photo out in the computer and just print a part of the original photo. Digital zoom does the same thing, but crops the photo in the camera.
Test Photos Comparing Optical and Digital Zoom
I needed to shoot a subject with a lot of detail, contrast and differing colors and tones for the photos to best illustrate the differences between optical and digital zooms, especially when printed in newsprint. Photos A, C and E were shot with a Samsung Galaxy S7 cell phone and photos B, D and F were shot with a Panasonic Lumix ZS60. The S7’s sensor has 12-megapixels and the Lumix has 16, but the S7’s smaller sensor contributes little to its loss of definition and sharpness when zooming into a scene. The S7’s digital zoom is the culprit while the Lumix’s optical zoom maintains a clear, sharp image at any of the lens’ focal lengths.
Photos A was shot at the S7’s widest angle, which is the only “zoom” setting when the S7 fully utilizes its 12 megapixel sensor. All other “zoom” settings use cropped areas of its sensor. Photo B was shot by the Lumix at an equivalent focal length to the S7’s wide-angle shot in photo A.
Photo C was shot at the S7’maximum digital zoom setting and photo D was shot with the Lumix’s optical zoom set to magnify its photo to equal the magnification of photo C. Photo D shows just how much detail the Lumix’s optical zoom captures compared with the S7’s mottled detail in photo C.
Lastly, to more dramatically emphasize how the two cameras produce very different qualities of photos when shooting telephoto images. Photo E is an enlarged area the S7’s photo C and photo F is an enlarged area of the Lumix’s photo D.
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So till next time, keep your eyes open, your camera handy and your imagination flowing.