Real Vs Zoom Distance

[Paul Gold Profile Private message]

Hi Gang -

Forgive me if this is photo 101, but - let's compare 2 images. The first is taken close enough so the subject fits the whole viewfinder. Now you go back 200 feet, but zoom so you get the same subject coverage. How do you tell which is which?

[gpsmikey Profile Private message]

There are several ways to tell which is which - some more obvious than others. First off, an image shot with a zoomed lens will tend to "shorten" the apparent distances between objects in view. Classic example - take someone outside with mountains or something in the background. Shoot one picture in the wide angle mode of them where they fill the viewfinder say 50%. Now shoot back up and zoom in to the telephoto mode to again get the same size of the subject and shoot that picture. In both shots, your subject is the same size in the image, but in the wide angle shot, the distant mountains or whatever are almost non-existent while in the telephoto shot, the mountains will be very noticeable. That is a classic mistake people make when they want scenery in the background - they shoot wide angle from close to the subject when it would work much better backing up and zooming in on the subject to bring the background in as well. An optically zoomed image tends to compress the apparent distances - objects in the background seem much closer. The wide angle does the reverse. For 35mm cameras, the 55 mm lens tended to have about the same effective focal length as the human eye and gave pictures that looked the way you remembered them.

Another way to tell the difference (and can often be used to your advantage) is the depth of field - on a wide angle shot, everything tends to be in focus. You shoot a picture of a flower in a field and everything around it is also in focus - back up and zoom in with the telephoto and the flower is still in focus, but things around it are now out of focus/blurred. (note that you can achieve a similar effect in Photoshop etc, but it is not the same)

Another issue with the "digital zoom" (either in a camera - I NEVER have that turned on in my cameras) or in Producer for example is it makes the apparent image larger, but it is not actually zooming in - there is no additional detail available than what was in the original image you are working with. Depending on the resolution of the original image, you can only zoom in so far before you start getting blocky pixelation of the image (there are some programs that can give apparent increase in digital zoom, but they don't actually add the missing details, all they do is work the problem of smoothing the pixelation out and sharpening the edges so it looks better.

hope that helps - there are very real differences in images that involve objects at multiple distances within the frame and it is important to recognize that those differences can not be resolved by "zooming" in later in some application. In a special case, if you were to ignore the resolution issues and were taking a picture of a flat surface at right angles to you (side of a building for example), it would be almost impossible to tell which was shot from close up and which had been "telephoto" and zoomed to match. Unfortunately, very few things out there are equidistant from you (flat surface) so all of the above applies

mikey