Historical Note on Enlargers

Photographic enlargers have existed since the earliest days of photography. The first enlarging system was described by Sir John Herschel in 1839. Since transparent negatives were not available until about 1850, all of the early enlargers were essentially large copy cameras. The problem for both copy cameras and negative-projection systems was to find bright-enough light sources so that exposures could be made in a reasonable amount of time. One solution was to use sunlight, and solar enlargers...

Visual Acuity

The acuity of the eye as an optical instrument is the easiest part to understand. As shown in Figure 14.4, the fovea, with a diameter of about 0.4 mm, subtends an arc of about 1 as required by the equation, arc length (focal length) x angle, where the focal length is 22.3 mm. This represents the angular range for high-acuity vision and is about twice the angle subtended by the sun or moon. This foveal diameter also corresponds to the area of 30,000 cones each having a radius of about 2 im....

Vignetting

The loss of intensity at the edges and particularly the corners of an image is known as vignetting (see Vignetting 09 ). This effect can be desirable for removing distractions and drawing attention to the center of a photograph, but unintentional vignetting is a defect that needs to be minimized or removed. There are at least three sources of vignetting. The most obvious one results from the obstruction of oblique rays by features in the lens barrel or lens attachments such as filters or hoods....

Derivation of the Lensmakers Equation

The lensmaker's equation for a thin lens is easily derived from the equations for the focusing powers of the two surfaces as described in Equation (7.1). The situation is illustrated in Figure C.1, where the radius of curvature for the second surface, R2, is a negative number. Now imagine that the two dagrams are overlapped, so that the lines defining the central plane of the thin lens coincide and the region having refrac tive index n2 is confined between the two curves. The result is that the...

Subjective Quality Factor

Our initial goal was to correlate perceived image quality with measurable properties of images. In 1972, Edward Granger, a senior scientist at Eastman Kodak, proposed an optical merit function that goes a long way toward accomplishing this goal. His work combined Crane s insight about the importance of the area under the MTF curve with research on the contrast sensitivity of the human visual system. What he did was to use CSF data to determine the most relevant part of the MTF for images of a...

And Monotone Images

There is some confusion about what constitutes a monochrome image. This confusion may arise because terminology in photography differs from that in traditional art. From color theory and photographic usage, it is clear that monochrome means black and white. In terms of the RGB color space, every pixel in the image must exhibit three identical values for R, G, and B. For example, the RGB values of a white region might be 255, 255, 255 and those for a black region will be close to 0, 0, 0. At...

The Depth of Field

So how can the DoF be expanded The laws of physics cannot be violated, and there is no way to capture an image that simultaneously offers high magnification (> 1X) and large DoF. There are, however, ways to combine a series of photographs obtained with different focal points to produce an image that appears to have a much larger depth of field than any one of the component images. This is a much more difficult task than stitching together images to increase the field of view or even combining...

Supplemental Lenses

Probably the easiest and least-expensive way to obtain close-up or even macro capability with a standard lens is to add a supplementary lens. The simplest of these is a one- or two-element screw-in lens that attaches just like a filter, although, of course, they are not filters. These close-up lenses are sometimes called diopters or plus diopters, because their strength is rated in diopters. (Recall that the optical strength is proportional to the inverse focal length, or d 1 f and the...

Compound Lenses

Compound Lenses

The focusing power of the lens, taking into account both surfaces, is characterized by the quantity 1 f. Now, suppose we have two thin lenses in contact as in Figure 7.3. What is the power of the combination This is an easy question that can be answered by combining the conjugate equations for the two lenses. First we introduce the labels 1 and 2 to obtain The image for the first lens falls to the right of the second lens and becomes its subject. Therefore, we can substitute -q1 for p2 in the...

Introduction

A number of severe problems are encountered in the design of wide-angle lenses with large apertures. First, there are the aberrations. Barrel distortion, where vertical and horizontal lines tend to bow out away from the center of the image, is common and corrections become more difficult as the focal length decreases. For example, full-frame 35 mm cameras have an image diagonal of 43.3 mm, and the smallest practical focal length for highly corrected, large-aperture, rectilinear lenses turns out...

Types of Fisheye Lenses

The equidistant projection fisheye also known as linear-scaled, angular, or ideal It is convenient for angular measurements, as in star maps. R f0 . The orthographic projection OP fisheye Nikon was able to implement the OP fisheye by using as-pheric lens elements. This lens gives an extreme fisheye effect with objects at the center made even larger and is useful for measuring illumination in architectural applications. This special-purpose lens is expensive and not very popular R f sin 0 . The...

Entrance Pupil Stop and Illumination of the Image

At this point, we want to consider the factors that determine the illumination of the image see Jacobson 09 . The brightness of the object is the first factor. Light from an object O is radiated into the cone defined by the halfangle Q, and a fraction of that light is transmitted by the optical system to the image I. The image is illuminated by a cone of rays defined by the halfangle Q' as shown in Figure 9.5. FIGURE 9.5. The object O, the optical system, and the illuminated image I. FIGURE...

Elementary Optics How Do Lenses Work

Let's fool the light, so that all the paths take exactly the same amount of time. I will begin with a few basic rules of optics and demonstrate how they work in simple lenses. Of course, science is not just a list of independent rules, and it should be recognized that these rules are derived from more general laws of physics. The rules are not only consistent with Maxwell's electromagnetic theory, but they can be derived from the quantum theory of photons and...

Color Theories

Modern theories of color begin with Isaac Newton 1642-1726 see Westfall 93 . Imagine the young Newton setting up a lens and a prism in his darkened room at Trinity College, Cambridge, in 1666. A ray of light from the window, defined by an aperture, is focused onto the prism. On the output side of the prism the ray is spread into a strip of light on a screen that glows with the colors of the rainbow. This experiment was not completely new others had seen colored...

UV and IR Photography

The human eye can only see a very narrow band of radiation between about 400 nm and 700 nm that is defined as the visible region. Thus we are restricted to a region of the electromagnetic radiation spectrum where the frequency varies by only a factor of 2. At first glance, this seems remarkable since the complete spectrum from gamma rays to radio waves encompasses almost 15 orders of magnitude change in frequency. However, humans evolved the ability to see sunlight, and most of the energy from...

Operation of the Visual Receptors

Wavelength 550 800 Absorption

To understand how the eye accomplishes high resolution and color vision as well, one needs to consider the visual receptors. There are about 130 million receptors in the retina. Of these, about 120 million are rods that are highly sensitive receptors containing the visual pigment rhodopsin. A rod can detect a single photon. The rods respond to blue green light and have maximum sensitivity at about 500 nm. They are responsible for night vision but permit no resolution of color. In addition,...

The Compound Lens

For the compound lens we begin with an approximate picture based on first-order optics. The thick lens shown in Figure 9.2, with its cardinal points principal and nodal and front and rear focal points is an idealization of a real compound lens. It is accurate for paraxial rays, i.e., rays near the optical axis, and making small angles with that axis. FIGURE 9.2. Image formation by a compound lens. The vertical lines P1 and P2 represent the first and second principal planes, and N1 and N2 are...

The Petzval

Petzval Sum

The great lens designer Rudolf Kingslake said, The design of any photographic lens is dominated by a certain mathematical expression known as the Petzval sum. He was referring to the specification of the image curvature that is produced by any simple or compound lens. This curvature, shown in Figure 8.4, is such an obvious characteristic of a simple lens that some opticians do not even regard it as an aberration. FIGURE 8.4. An illustration of image curvature. FIGURE 8.4. An illustration of...

The Thin Lens

Thin Lense Refraction

A thin lens, as shown in Figure 9.1, has an axial thickness that is much less than the lens diameter and the focal length, and distances along the axis can be measured from the central plane of the lens. Rays, from objects to the left, that are parallel to the optical axis, after refraction, are focused at F2, the rear principal focus point. For objects at less than infinite distances, a real image will always be formed at a distance greater than f from the lens. The imaging properties of this...

Accomplish Their Magic

Refractive Index Fish Eye View

The term fish-eye view was introduced into photography by Robert Wood, who was an optical physicist at Johns Hopkins University. In his text Physical Optics Wood 11 , he invited the reader to consider the outside world as viewed by a fish. Directly overhead objects would be seen clearly but away from the vertical direction there would be distortion. Also, beyond a critical angle, the surface of the water would be a mirror because of total internal reflection. The effect can be quantitatively...

Examples and Illustrations

Fisheye Correction

Standard fisheye lenses for 35 mm cameras give 180 fields of view and are available in two types. Fisheye lenses with focal lengths in the range 6-8 mm fit the complete 180 field-of-view full circle disk into the narrow dimension of the image, while full-frame fisheye lenses with focal lengths of 14-16 mm spread the hemispherical image across the film or detector diagonal, e.g., 43.3 mm for FF sensors as shown in Figure 10.7. The most widely used DSLR cameras have sensors that are approximately...

Of Image Appearance

We can maintain the angle of view by scaling the focal length f as shown in Figure 11.1. If the lens on the FF camera is set for 60 mm then the P amp S must be set to 60 mm 6 10 mm. FIGURE 11.1. The horizontal angle of view for FF sensor focal length 60 mm and P amp S sensor focal length 10 mm . By scaling the focal length so that it is proportional to the sensor width, we have obtained an image that is similar in one way, but it may not really be equivalent when the other...

Optical Surfaces

No matter how complicated a lens is, it still consists of optical surfaces separating regions that have different indices of refraction and, in principle, all we need is Snell's law of refraction to be able to trace the path of a ray of light through a lens. This idea is illustrated in Figure 7.1, where a ray of light red is incident on a spherical surface at a distance h from the optical axis. The surface is characterized by the radius of curvature R since the center of curvature is on the...

The Camera Body

In the first few decades after the invention of photography, the way to make a larger photograph was to use a larger camera. In spite of efforts to develop enlargers for photographs, many professional photographers preferred large plate film cameras. It is reported that William Henry Jackson hauled a 20 in. x 24 in. glass-plate camera on mule-back to photograph the western mountains. Also, Ansel Adams 1902-1984 often used a camera with 8 in. x 10 in. film plates. But certainly George R....

Science for the Curious Photographer

An Introduction to the Science of Photography Editorial, Sales, and Customer Service Office Copyright 2010 by Charles S. Johnson, Jr. All rights reserved. No part of the material protected by this copyright notice may be reproduced or utilized in any form, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission from the copyright owner. The following products and trademarks are used throughout the book AT amp T...