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An inspirational bible for monochrome photography - this second edition almost doubles the content of its predecessor showing you the path from visualization to print
An inspirational bible for monochrome photography - this second edition almost doubles the content of its predecessor showing you the path from visualization to print
Now you see it, now you don't
Photography is a form of visual communication and a category of modern visual art, which simply means that photographs are made to be seen by a group of people other than the artist himself. Successful artists, by intent or by instinct, make use of the fundamentals of human visual perception to improve their works of art. The human reaction to an image is a complex mix of physics, emotion and experience. However, understanding the limits of human vision allows the photographer to distinguish between essential and irrelevant technical accomplishment.
Three essential components are required to make human vision possible. There must be a sufficient amount of light, a light-gathering device to receive and arrange the light into structured optical information, and a processor to sort and administer this information to make it available for further decision and action. In the human visual system, eye and brain work closely together to gather, arrange and process the light around us.
Electromagnetic Spectrum and Light
Modern humans are constantly exposed to a wide range of electromagnetic radiation (fig.1), but we hardly ever think about it, because our daily lives are filled with radio and television signals, radar, microwaves and the occasional x-ray exposure at the doctor's office. Low-frequency radiation, such as in radio and television signals, carries little energy and has no effect on the human body. It cannot be seen or felt. Higher frequencies, such as infrared radiation, can be felt by the skin as warmth, and even higher frequencies, such as UV and x-rays, carry sufficient energy to be harmful to humans with prolonged exposures. The highest frequencies, such as gamma radiation and cosmic rays, are packed with energy and would put an end to life on earth, if it were not for the planet's sensitive atmosphere and its strong magnetic field to protect us. However, most electromagnetic radiation bombards us constantly without ever being detected by any of our senses. There is only a tiny range of frequencies, with a wavelength from roughly 400-700 nm, to which our eyes are sensitive. It is the visible part of the electromagnetic spectrum, better known as 'light'. Within this range, the human eye sees changes in wavelength as a change of hue.
The Anatomy of Human Vision
Before we get into the human visual system as a whole, it makes sense to initially understand the optical performance and visual functionality of eye and brain individually. What may come across as a small lesson in human anatomy is actually an essential introduction to the basic phenomena of human vision.
The Human Eye
The human eye is often compared to a photographic camera, because the eye, a sophisticated organ capable of focusing an image onto a light-sensitive surface, is very similar to lens, camera and film (fig.2a), but with some significant differences in operation. The eye is a light-tight hollow sphere (sclera), containing an optical system (cornea and lens), which focuses the incoming light onto a light-sensitive surface (retina) to create an upside-down and reversed image. The amount of incoming light is controlled by the iris, which adjusts the aperture (pupil) as needed. The retinal image is converted into electrical impulses by millions of light-sensitive receptors and transmitted to the brain via the optical nerve.
Sharp focusing is controlled by the ring-shaped ciliary muscle, which surrounds the lens and is able to change its curvature. The muscle contracts to bulge the lens, allowing us to focus on nearby objects, and it relaxes or expands to flatten the lens for far-distance viewing. Changing the optical power of the lens, to maintain clear focus as the viewing distance changes, is a process known as accommodation. As we get older, the lens loses its flexibility, and it becomes increasingly more difficult to focus on close objects.
At infinity focus, the average lens has a focal length of roughly 17 mm. When fully open and adapted to low light levels, the pupil has a diameter of about 8 mm, which the iris can quickly reduce to about 2 mm in order to compensate for very bright conditions and to protect the retina from irreversible damage. In photographic terms, this is equivalent to an f/stop range from f/2 to f/8, covering a subject brightness range of 4 stops or a 16:1 ratio.
The retina is lined with light-sensitive receptors of two types, called rods and cones, which are only responsive to dim and bright light, respectively. At any given time, rods and cones provide a static sensitivity range of about 6 stops. However, rods and cones are able to dynamically alter their sensitivity by regulating the amount of a light-sensitive dye they contain. This enables the retina to adapt to a light-intensity range of 1,000,000:1 and adds 20 stops of dynamic sensitivity to its static range.
Fully building up the light-sensitive dye takes about 8 minutes in cones and up to 30 minutes in rods, which is a process called dark-adaptation. This explains why our vision improves only slowly, when we move from a bright to a dimly lit room. In the reverse process, rods and cones rapidly dispose of the dye, in order to safely adapt to a brighter environment. This is referred to as light adaptation and is typically completed within 5 minutes.
All rods are of a similar design, highly specialized for low-light sensitivity. However, cones come in three different varieties, and each kind produces a slightly different type of dye, making it sensitive to a different wavelength of light. This enables color vision, very similar to the way red, green and blue color receptors enable color imaging in digital camera sensors.
In summary, rods give us sensitive night vision (scotopic) and cones add colorful day vision (photopic) to our sense of sight (fig.2b). Combining the static and dynamic sensitivity range of the retina, and adding the light-regulating support of the iris, provides the human eye with an enormous sensitivity range of 1,000,000,000:1 or almost 30 f/stops, as long as we give it the time to adapt to the dimmest and brightest lighting conditions possible.
There are millions of rods and cones distributed across the retina, but unlike the light-sensitive particles of a silver-gelatin emulsion, rods and cones are not distributed uniformly (fig.2c). Rods predominantly populate the outer surface area of the retina, whereas cones are primarily found around the center. Furthermore, there are two small areas on the retina that are quite different from the rest, and they deserve some special attention.
Close to the center of the retina is a small indentation, called the fovea. Its center, the fovea centralis, which is also the center of human vision, is only 1 mm in diameter. The fovea contains almost exclusively cones and very few rods. In fact, nowhere else on the retina are cones so densely populated as in the fovea. Here, the distance between cones is as small as 2.5 µm, and because of this, humans have excellent visual acuity in bright light. However, peak performance is limited to a relatively small angle of view, only a few degrees, concentrated around the fovea (fig.2d). Everything outside this narrow field of view blends into our relatively fuzzy peripheral vision. Nevertheless, about 50% of the optical impulses, sent to the brain, come from the fovea, and therefore, we can assume an optical resolution of the human eye of at least 30-60 line pairs per degree. The optical resolution of the eye also depends on the diameter of the pupil or, consequently, on illumination levels. Similar to a photographic lens, overall optical performance increases with decreasing aperture until diffraction takes over. Fig.2e shows how a wide-open pupil (8 mm) is limited to 30 lp/degree, a normal pupil opening (4 mm) achieves about 60 lp/ mm, and a very small pupil (2 mm) can resolve up to 90 lp/mm. For the purpose of viewing photographs, we can assume an optical resolution of the human eye of 30-90 lp/mm, which is equivalent to viewing angles of 20-60 arc minutes and covers the range from standard to critical viewing conditions.
About 20° from the center of the fovea is the optical disc. This is the location where the optical nerve is attached to the eye. The optical disc is entirely free of rods or cones, and this complete lack of light receptors is the reason why the optical disc is also referred to as the 'blind spot'. Amazingly, the blind spot does not disturb human vision at all, because the brain makes use of surrounding optical impulses in order to fill in for the missing image information.
The Human Brain
Comparing the human eye to a camera and lens does not fully appreciate the sophisticated functionality of this complex organ, but it sufficiently illustrates the eye's contribution to the human visual system. A similar association is often made by comparing the human brain to an electronic computer. The speed with which our brain processes visual input is about the only realistic comparison we can obtain from this analogy, because the brain is much more than just a pile of electronic circuitry.
The eye focuses an upside-down and reversed image onto the retina, where rods and cones convert the optical sensation into electrical signals, which travel along the optical nerve to several areas of the brain for subsequent processing. At first, the visual cortex, which is an area in the occipital lobe of the brain at the back of our head, differentiates between light and shadow, making out borders and edges and combining them into simple shapes. With support of the cerebral cortex in the parietal lobe, the new data is compared with previously memorized information and used to quickly recognize familiar faces and objects, while separating them from the background. But, visual processing does not stop there, because the information is now passed to the temporal lobe, where the meaning of what we have seen is interpreted, and faces and objects are given a name. In the frontal lobe, feelings are added, and finally, in the prefrontal lobe, we order our thoughts and decide what to do next, based on what we have seen.
This is a very simplified overview of the brain's function as part of the human visual system. What actually happens in our heads is far more complex, and much of the brain's functionality is still a mystery to modern science. All we know for sure is that whatever our brain does, it does it very, very quickly.
The Human Visual System
The human eye is a camera, and the brain is a fast computer. While this grossly oversimplified statement roughly explains the contribution of both organs to human vision, it cannot illustrate the complexity and sophistication of the human visual system. What we believe to 'see' is a combination of the images created by our eyes and the brain's interpretation of them. In addition, the brain constantly supports the eye to optimize its optical performance and get the most visual information possible. Here are two examples:
The eye is able to recognize minute detail far beyond its inherent optical resolution of 1 arc minute. We can easily distinguish a thin wire against a bright sky down to 1 second of arc, but visual angles alone cannot explain why we can see the dim light of a star, thousands of light-years away. This astonishing capability is only possible with the support from the brain, because in reality, we do not look at a scene in fixed steadiness. Instead, our brain controls a constant and rapid scanning of the scene, referred to as saccadic movement, in an effort to gather more information than static observation alone would permit.
In addition, the brain keeps the eye in a constant state of vibration, oscillating it at a frequency of about 50 Hz. These subconscious micro tremors are involuntary, small angular movements of roughly 20 arc seconds, and they help to constantly refresh the retinal image produced by rods and cones. Without these micro tremors, staring at something would cause the human vision system to cease after a few seconds, because rods and cones do not record absolute brightness values but only respond to changes in luminance. The combined effort of saccadic movement and micro tremors are the reason for the amazing optical resolution of human vision and often the explanation for otherwise puzzling optical illusions.
The next example illustrates how our brain compensates for a natural deficiency of the human eye, and the large role the brain plays in determining what we see. From fig.2a, we know that there is a small area on the retina without visual receptors, called the optical disc, and a simple test will reveal its existence.
Fig.5 shows a plus sign on the left and a black dot to the right. Close or cover your left eye, and firmly stare at the plus sign with your right eye. While keeping your left eye closed, slowly move your head closer to the book. Keep staring at the plus sign, but be aware of the black dot on the right with your peripheral vision. At a distance of about 8 inches or 200 mm, the black dot suddenly disappears, at which point, its image falls on the blind spot of the retina. It may take you a few trial runs to get comfortable with this test.
Note that the brain is not willing to accept the lack of visual information caused by the blind spot. It does not disturb our normal vision, because the brain simply takes some visual information from the surrounding areas and fills in the blank spot with what, in reality, does not exist.
The last two examples demonstrated how the brain makes the most of the optical information it receives from the eyes. But, as we will see in the next example, sometimes the optical information only serves as supporting reference data for the brain to make a quick judgment.
Find yourself a willing participant and cover fig.6 with a piece of paper. Ask your test person to look at fig.6 and to uncover it for less than a second. Now, ask the person what playing cards he or she remembers seeing. Most people claim to have seen a king of hearts and an ace of spades. A more thorough observation of fig.6 reveals that the card on the right is actually a fake, black ace of hearts.
Of course, the official deck of playing cards contains no black ace of hearts, and consequently, the brain refuses to take the optical information given at face value, and prefers the result of a comparison with its previous experience, instead. The brain's conclusion is that the optical information, received from the eyes, must be wrong for whatever reason, and the card seen is more likely a common ace of spades. Nevertheless, a long enough look at fig.6 will eventually convince the brain that a black ace of hearts does indeed exist, and the test cannot be repeated with the same person, because its memory now allows for the existence of a black ace of hearts.
Human behaviorists believe that our brain is designed to make speedy decisions to protect us. When it comes to our safety, we need quick decisions. For example, the decision whether it is safe to cross a busy road or not does not rely on time-consuming calculations, considering the laws of physics. It's done within a split second, based on experience.
Less so in modern life, but very important to prehistoric human survival, was the ability to quickly separate enemy from friend. A familiar friendly face poses less of a threat than the uncertainty of an encounter with a stranger or the frightening appearance of a known enemy, who has done us harm in the past. For this reason, a large portion of our brain is dedicated to face recognition, and it works extremely well.
It works so well, in fact, that logic and reality are often forced to take second place. Faces seem to be hiding everywhere. We can detect them in bathroom tiles, wallpaper patterns and cloud formations. Our brain is constantly on the look out for facial features. Without the human obsession with faces, there probably would not be a man in the moon.
Experienced photographers and creative artists are aware, and make use, of the importance and power of facial expressions. The lead picture, 'Migrant Mother' by Dorothea Lange, does not reveal the actual circumstances where, when and why it was taken, but it summarizes the unfortunate fate of an entire family through the emotions written on one face.
Excerpted from Way Beyond Monochrome by Ralph W. Lambrecht Chris Woodhouse Copyright © 2011 by Ralph W. Lambrecht and Chris Woodhouse. Excerpted by permission of Focal Press. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Part 1 The Basics
From Visualization to Print
Eye and Brain
Fundamental Print Control
Timing Print Exposures
Paper and Print Contrast
Basics of Photographic Printing
Archival Print Processing
Presentation is Everything
Mounting and Matting Prints
Framing and Displaying Prints
What Size is the Edition?
Part 2 The Science
Introduction to the Zone System
Introduction to Sensitometry
Sharpness and Depth of Field
Basics of Digital Capture
Digital Capture Alternatives
Introduction to Exposure
Development and Film Processing
Creating a Standard
Customizing Film Speed and Development
Influence of Exposure and Development
Applied Zone Systems
C41 Zone System
Masking for Complete Control
Digital Negatives for Contact Printing
The Copy-Print Process
Advanced Print Control
Fine-Tuning Print Exposure & Contrast
Measuring Paper Contrast
Contrast Control with Color Enlargers
Exposure Compensation for Contrast Change
Basic Split-Grade Printing
Advanced Split-Grade Printing
Paper Reciprocity Failure
Miscellaneous Material Characteristics
Above Malham Cove
Portrait Studio Lighting
St. Mary's of Buttsbury
Part 3 Odds and Ends
Equipment and Facilities
How Safe is Your Safelight?
Enlarger Light Sources
Sharpness in the Darkroom
Other Darkroom Equipment
Tool, Tips and Tricks
Identification System for Film Holders
Hhow to Build andUse the Zone Ruler
How to Build and Use a Zone Dial
Make Your Own Shutter Tester
Make Your Own Test Strip Printer
Make Your Own Burning Card
Exposure, Development and Printing Records
Making Prints from Paper Negatives
Make Your Own Transfer Function
Basic Chemical Recipes
Tables and Templates
Posted November 7, 2012
The book is a real achievement, almost an encyclopaedic reference. I got inundated with the sheer technical content it's brimming with. In my view, the book is itself a complete photography course.Was this review helpful? Yes NoThank you for your feedback. Report this reviewThank you, this review has been flagged.