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What is Depth of Field?

Depth of field is a range interval in front of a camera, within which the photo appears sharp. Or to be more precise: A regular camera can focus at one distance at a time only and the best image definition on a photo appears for objects located there. However, the same photo may also have tolerably sharp resolution within an interval around this 'best' focus: That's what we call the Depth of Field, apparently the interval from 80 to 100 centimeters on this single-shot test photo, taken with a FocOz camera, 3x tele lens (f=20mm) and full aperture F/2,6 focused at 90 centimeters.


The classic way to improve (increase) this range is to reduce the lens aperture, i.e., increase the F-number (here to F/8).

This image shows the effect of changing aperture

Zooming for shorter focal length will also do.

Different apertures

It works, but there are constraints: Small apertures reduce light transmission, giving long exposure times and as a consequence, motion blur. And too small apertures suffer from light diffraction, degrading the image resolution. The FocOz camera brings the nearest depth of field limit down to 3 centimeters and all the way up to the horizon (infinity) with full aperture and without these limitations.

Evolution of Photography

The principle of projecting an image through a small pinhole onto the wall of a dark room (or box) may have been anticipated by ancient Chinese thinkers, and was known more than 1000 years ago by Arab astronomers, later improved by Leonardo da Vinci and further developed by adding a small lens in that pinhole, becoming a camera obscura. (1)

The invention of light sensitive emulsion made it possible to record images permanently in the same camera obscura - giving us the first generally useful cameras (Daguerre) from the 1830s. Development of high resolution roll film for cameras of reduced size meant better depth of field in so-called Fixed-Focus cameras for the general public of the next century, and the 1977 invention of Autofocus (AF) made focusing cameras much easier. But: Still one focus only for each exposure.

Zeiss Ikon (left) Kodak Brownie No 2a (1910)

The development of large-aperture, high-resolution lenses made the Depth of Field issue more critical again, although the recent development of digital cameras with small sensors has improved the depth of field situation to a certain degree.

Long and fast telephoto lens and CMOS image sensor

Extending the Depth of Field

So there we are: The old Depth of Field problem within photography is obviously still there! But Digital camera technique provides us with a key to remedy this problem: You may record several differently focused frames of one and the same scene. Each of these shots has its own Depth of Field around a focus, but they may overlap each other, together constituting a merged continuous Depth of Field, even stretching over the whole focusing range of a camera lens. It's feasible to do so with the FocOz camera, where compound photos with a continuous depth of field from 3 centimeters (Supermacro proximity distance) up to the horizon (infinity) are regularly attempted. In order to achieve this, you must merge the differently-focused frames in such a way that only the best focused parts from each frame are kept for a final (processed) picture while the blurred rest is rejected. This is done with a FocOz image processing computer program, specially developed for this purpose.

I know that some of you may object that you don't need any Depth of Field extension. Fair enough: Sometimes we prefer to blur a background in order to bring out the foreground. It's an old tradition within photography to transform this technical shortcoming into an advantage.

The Old Masters

The old masters made oil paintings with 'Infinite Depth of Field': They painted what they saw - and their eyes accommodated (focused) onto each individual object, depicting them sharply one after another.

The 1467 AD portrait below is an example of that (Hans Memlinc):

Hans Memlinc

Even modern art shows evidence of Infinite Depth of Field, like this AD 1998 painting by Dietrich Varez (Hawaii) below:

Dietrich Varez

Image Information

Infinite Depth of Field photos, made with the FocOz camera, also have more image information than the individual shots from which they originate. This is indicated by reading original (jpg) file sizes for these pictures: The merged FocOz picture file is usually bigger, as evidenced here:

Example of FocOz picture

It may sometimes be the purpose of a photographer to record as much detail as possible, like at a press conference with several prominent participants sitting along a table. Or you may wish to make a close up view of some flowers, at the same time documenting the rest of the garden. Here is an example:


Extended depth of field may help you in such cases, adding more information to the photo. We have made many such shots during the past few years and find that the extended depth of Field of a FocOz camera adds quality, information, and appeal to a picture.

(1) a darkened enclosure having an aperture usually provided with a lens through which light from external objects enter to form an image of the objects on the opposite surface. (up to "Evolution...")

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