Most people are familiar with the concept of zooming, but I’ve found that few understand the difference between optical and digital zooming. As a result, many travelers are devastated when they come home from a fabulous trip, with highly digitally zoomed photographs, to find them blurry, with the jaggies, and lots of noise.
In optical zooming, the individual pieces of glass (The are the glass elements -seen above in the cutaway view of the lens; the vertical pieces in the photo having convex and concave shapes.) of the lens are mechanically moved to manipulate the image the photographer wants to capture. By realigning the glass elements of the lens, the subject of the image is either magnified or reduced in size, with the angle of view either narrowed or expanded.
When zooming optically, all the magnification or reduction of the subject in the image is manipulated by the lens itself, so that the photograph captured uses the entire sensor area of the digital camera. This is true from the widest angle shot (wide angle focal length) with the least magnification, to the narrowest angle shot (telephoto focal length) with the maximum magnification.
In the photo above of surfers at Hookipa Beach State Park in Maui, Hawaii, note how sharp the image of the surfers and the water is. The photograph was taken from more than a quarter of mile away, with an 80–400mm zoom lens set at 400mm, then highly cropped. Because the zooming was completely optical, the quality of the image was maintained, even at the longest possible focal length of the lens.
In the strictest sense of the term, digital zooming is not really zooming at all. When you use the digital zoom in a camera, the camera enlarges a portion of the image. It simulates optical zooming. The camera crops a portion of the image and then enlarges it back to the full size of the camera’s sensor, thus “magnifying” the subject of the image.
Digital zooming does not focus in as the lens zooms closer and closer, as optical zooming does.
In the camera’s digital zoom magnification process, in order to fill the sensor with the cropped image (The size of the cropping is determined by the camera’s zoom setting. The higher the zoom, the smaller the cropped portion of the image.) the camera interpolates the image as it spreads it out, adding new pixels it creates to fill-out the image. The camera’s internal computer creates these pixels by sampling the nearby pixels from the original image. As the magnification, due to the zoom setting, increases, the more spread out the original image becomes, causing the camera to need to create more and more pixels to complete the image.
This may or may not yield a satisfactory result, according to your expectations. More often that not, the image will be noisy, have jagged edges, and be somewhat blurry. The more digital zoom used, the worse the quality of the photograph.
If you don’t need digital zoom, but have been generally using it instead of optical zoom or to augment it, without realizing how it works, and wondered why your pictures did not look that great, now you know.
Sacrificing image quality by using digital zoom to capture the moment is sometimes more important than not getting the picture at all, however I’ve found that most of the time, using digital zoom is unsatisfactory for any reason.
In the photo directly above, of the surfers in Hawaii, I’ve simulated the use of a moderate amount of digital zoom. To me the photo is wholly unsatisfactory, and in truth, if someone tried to capture this shot with a digital point and shoot camera, using digital zoom, the photo would be far worse. The detail of facial features is gone and there is a great deal of noise in the photo. The small size of the image in part belies just how bad it is.
A few years back I was taking a photography seminar. I remember the instructor’s words well when he talked about digital zooming. “Don’t be fooled. Digital zoom is all about selling cameras. It’s strictly a marketing scheme to entice newbies who don’t know any better, to buy their cameras because of a huge zoom number.”
I tell anyone who asks me about digital zoom, “Turn if off and forget about it, but … if it’s the only way you can capture an image you’ve got to have, try it, but the odds are you’ll throw away the photo later.”