Photography Lesson 2 Pinhole Camera Lenses

The Pinhole Camera

as light strikes an object, it is reflected, scattered in all directions

here we see the light that is scattered from a single point on this apple. the light travels in virtually every direction simultaneously, and strikes a flat surface multiple times

Imagine that there is a wall with a tiny opening in it between the apple and a reflective surface. Only the light that is traveling in a straight line from one particular point on the apple will pass through the opening.

if we follow the path of light from any other point on this apple, the same result occurs

every point on the apple will reflect light that will travel in a straight line through the aperture. The light from each of these points forms an inverted image on any surface opposite the aperture.

when the back wall is enclosed in a darkened chamber, this simple design is known as a pinhole camera. Typically, light sensitive film would be placed against the back wall.

Pinhole cameras require very small apertures that are typically made with a pin-prick. As light passes through the small aperture, it produces a small, accurate circle of colored light.

Pinhole cameras characteristically let very little light in through their small openings, and therefore must compensate with relatively longer exposures.

A larger opening on a pinhole camera would not produce satisfactory results. The light that enters a larger opening spreads out before it hits the surface of the film.

Soft, overlapping circles result, producing an out of focus image. While the exposure time will certainly be lessened, this comes at the expense of focus.

a Lens solves both of these issues, allowing sharper focus and shorter exposure time.

The Lens

From Pinhole to Lens A pinhole, as small as it is actually admits a cluster of light rays. Coming at slightly different angles, these rays continue through the hole in slightly different directions. A Lens creates a sharp image with relatively short exposure. To get sharp pictures, the image of a tiny point should also be a tiny point

The most important way lenses differ is in their focal length. Technically, focal length is the distance between the lens’s rear nodal point and the focal plane when the lens is focused at infinity. Focal length controls magnification, the size of the image formed by the lens. The longer the lens, the greater the size of objects in the image. Focal length also controls the angle of view, the amount of the scene shown on a given size of film

Normal-focal-length lens, also called a standard-focal-length lens, approximates the impression human vision gives. - faster Long-focal-length lens provides greater image magnification and a narrower angle of view than a normal lens. Long lenses are excellent when you can not or do not want to get close to the subject. – slower A short-focal-length lens increases the angle of view and shows more of a scene than a normal lens used from the same position. – wide angle lens

Zoom Lens Zoom lenses are popular because they combine a range of focal lengths into one lens. Using a 28 – 105mm zoom is like having a 28mm, 50mm, 85mm, and 105mm lens instantly available, plus any focal length in between. Zoom lenses tend to be a little bit heavier, more expensive, and bulkier. Zoom lenses are best used where light is ample because they have a relatively small maximum aperture. Zooms that keep the same aperture at all focal lengths are complex designs and therefore relatively expensive.

Macro A macro lens is useful for extremely close shots

Fisheye For the widest of wide-angle views, consider the fisheye lens.

Focus and Depth of Field As we’ve discussed, You can use the aperture to control the depth of field. There are two other ways to control or adjust your depth of field. –Focal length –Distance from the subject.

Again, the smaller the aperture, the greater the depth of field. same focal length, staying at the same distance

The shorter the focal length of the lens, the greater the depth of field. Same aperture, set at same distance

The greater the distance from the subject, the greater the depth of field. The pic on the left was taken at 3ft, the pic on the right, from the same lens and focal length with same aperture from 10ft farther away.

Why does a lens of longer focal length produce less depth of field than a shorter lens used at the same f-stop?

Equivalent Exposure 1/500 = 1/125 1/15 =‘s ? 1/250