Camera concept and calculation of depth of field

First explain some concepts: 1, focus (focus) and the optical axis parallel rays into convex lens, ideal lens should be all rays accumulation in mind, then to the proliferation of the cone, the aggregation of all light, known as the focus. 2. circles (circle of confusion) before and after in focus, light began to gather and spread, the point of the image becomes fuzzy

To introduce a few concepts:

1. focus (focus)

And the optical axis parallel rays into convex lens, ideal lens should be all rays accumulation in mind, then to the proliferation of the cone, the aggregation of all light, known as the focus.

2. circles (circle of confusion)

In focus, light began to gather and spread, the point of the image become blurred, resulting in a widening of the circle, the circle is called circles.

In reality, the ornamental images filmed is in some way (such as projection, zoom into photos, etc.) to watch, people feel of Visual image and the magnification, projection distance and viewing distance has a lot to do, if circles of diameter less than differential ability of the human eye, in a certain range of actual image blurring is not identifiable.

This will not be able to pick out the circles is called permissible circle (permissible circle of confusion).

Of different manufacturers, different film area has different permissible circle diameter of numerical definition.

Most commonly used are:

Medium format

24mm x 36mm

6cm x 9cm

4" x 5"

Dispersion circle diameter

0.035mm

0.0817mm

0.146mm

35mm photographic lens of permissible circle, is approximately the length of diagonal film 1/1000 ~ 1/1500 or so.

The premise is that the screen magnification for 5x7 inches photos, observation distance 25 ~ 30cm.

3. depth (depth of field)

In focus before and after a permissible circle, these two circles distance is called depth of field, namely: Photo subjects (on focus), the image is still a clear scope, depth of field.

In other words, be taken field.in, rendered in the film surface image fuzzy degree, are permissible circle of limited extent.

Depth of field with the lens focal length, aperture value, shooting distance.

For fixed focal length and shooting distance, Aperture, depth of field.

To hold the camera photographer, from the focus to a nearer permissible circle distance call prospects deep, far away from the focus to the permissible circle distance is called after the depth of field.