Digital Zoom, What is it?

It's that time once again...time for another installment of Tips and Tricks. It is here that I try to answer some questions that I get asked in a bit more detail than I care to do in an email. These topics are selected because of their potential range of interest and this topic has come up several times. I'm sure you have wondered the same thing before, I know I have....What is digital zoom and why is it different than optical zoom?

This will only apply to those that use a digital point and shoot camera. Neither film, nor DSLR (Digital Single Lens Reflex) owners have the option of digital zoom. So...what I'm saying is that a digital point and shoot is more advanced than these other cameras? Yes and no.

Here's the deal...any lens on any camera has a range of zoom, or focal length. For instance, the kit lens on a Canon Rebel DSLR has a range of 18mm-55mm. This represents the focal lengths that the lens is capable of working within. This is it folks, if you want to work outside of that range, either wider or longer (zoomed in), you will need to invest in a new lens. The lens on my primary Sony camera is a 28mm-200mm lens in terms of optical zoom. I do have the option of turning on the digital zoom which will increase the zoom to 400mm (2x digital zoom). Honestly, I have never once used this feature, and don't intend to. Why not? you ask. Lets dive right in, shall we.

Optical Zoom

I'm sure you have heard this term before when looking at cameras, or perhaps reading your instruction manual. What does this mean? Simply put, it means that the camera is working within the boundaries of the lens. For illustration purposes, I have made use of my secondary camera, a Sony MVC-FD200 which has an optical zoom range of 41mm-123mm in 35mm format (taking into consideration the sensor size). The image captured within this range will be at top resolution for the camera and reproduced as the sensor "sees" the image from the lens.

At wide angle (41mm), the camera is recording detail from its widest field of view.

What we will be focusing on is the mail box in the center of the picture. As we go through the stages of zoom, keep your eyes on the mail box.

You will recall that the highest optical zoom for this camera is 123mm. That is the longest focal length that this camera can optically resolve between the lens and the sensor.

Look at the cut out in the upper right corner. This is approximately a 1x1 inch cut out. You can make out the numbers on the mailbox, and the post and reflector appear just a slight bit fuzzy. This is more dealing with the very small sensor size of this camera rather than the issues we are discussing. The main thing is that this all looks smooth and natural. When printed, it will have the same quality as the wide angle setting.

Digital Zoom

If we were wanting to get in closer, but were unable to walk to close the distance, the only available option is to activate the digital zoom feature. With the MVC-FD200, the digital zoom is a 2x zoom which means that it will double the zoom over optical. In this case, we can stretch our focal length to a whopping 246mm in 35mm format.

Hey, this is great!! Where a DSLR owner has to go out and buy a new lens with a hefty price tag, the point and shoot owner gets to select a menu option that allows them get get really close in. Not so fast...while this might appear like the digital equivalent of a shot of nitrous oxide in your car, it is not all its cracked up to be. Notice the noise that is evident in the street, the harsh edges, and the chromatic aberrations evident between light and dark tones. This is about a 1x1 inch cutout that would be indicative of how the whole picture would appear printed out. Now you are starting to see the problems with digital zoom.

Printing, where the rubber meets the road

The best way to explain the difference in optical vs digital zoom, is to explain what happens inside the camera to produce the image. There are two main ways of getting this digital zoom, and both of them reduce the effective resolution of the image. While this might not be a big deal when viewing the image on a monitor, or using the image as a factual record, it will not work as well when printed as art, or as a framed picture.

The most common method of digital zoom is where the camera takes the maximum optical zoom and digitally increases the size of the center. To do this, the camera will interpolate the lost information when the now smaller image is stretched back to full size. Effectively, the camera creates pixels of the color that it thinks should go in the holes. This can work up to a point, but will lead to lots of digital noise, as well as pixelation in the image. The example above is using this this form of digital zoom.

The camera is a 2MP (mega pixel, 2,000,000 pixels of data) camera and the file saved is a 2MP file, however, the information is taken from only a 1MP image and stretched out. Now you are starting to see the problem. Even though the saved picture shows to be a full size 2MP image, it is nowhere near the same quality. Imagine the difference with an 8MP camera only using data from 4MP worth of the sensor.

In an attempt to gain some quality back, Sony pioneered a "smart zoom" which is also a formof digital zoom. In this case, the camera is set to a lower than top resolution. Again, using an 8MP example, the resolution would be set originally to 5MP. When the smart zoom is turned on, the camera will capture an 8MP image, but will delete the pixels from the outer edge until there is only a 5MP image left. You then have a bit of zoom beyond the optical zoom, without losing resolution. The caveat here is that you are now shooting at 5MP which will reduce the size of the picture that you can print at top quality. If you are printing small, then this will not be an issue and you will have a little more zoom available to you. While you don't get the problems associated with the interpolation of pixels, there is the reduced resolution of the image which will directly impact the maximum size of the printed image.

Final Thoughts

As you can see, there is more to zoom in a point and shoot camera than you realized. So is digital zoom a bad thing....no, not at all. Is it a tool that can be used effectively....yes it can. However, for those of us that enjoy printing out top quality images in large sizes, digital zoom is the death of an image. The only true way to achieve a longer focal length with photographic quality, is with a lens of the desired focal length.

When it all boils down...if the picture is worth taking, it is worth taking well.

Written by Greg A. Kiser