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Proceedings
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The Field Of Education In The National Parks
The Educational Program And Its Place In National Parks Administration
Administration Of Park Museums
Scientific Aspects Of The Park Protection Program
The Research Program In The National Parks
Use Of Recorded Scientific Data
Libraries In The National Parks
Photography And Visual Education
General Administrative Problems
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Proceedings Of The
First Park Naturalists' Training Conference Held At Educational
Headquarters, Berkeley, California:
November 1-30, 1929 |
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PHOTOGRAPHY AND VISUAL EDUCATION
PRINCIPLES OF PHOTOGRAPHY
By George A. Grant
It had been known for many years that certain substances containing silver were blackened when exposed to light for some time. Later on it was found that when some of those substances were exposed for a very short time, so short in fact that no blackening could be noticed, nevertheless a change took place which caused them to darken when treated with certain chemicals. The whole art of photography is based on these observations. If we should prepare one of these silver compounds, mix it with gelatine so as to form a thick paste, spread it on a glass plate or film today, what we would have would be practically the ordinary dry plate or film.
A camera must have three elements: A light proof box, a lens to project the image, and a plate holder. We will take up the lens later. But assuming that an image has been projected through the lens from the reflected lights on an object outside the camera and thrown on the sensitive plate, this is what happens. The parts of the image containing the strongest light will make the greatest impression on the sensitive silver plate or film. The weaker lights will make a weaker impression, and so on down to the shadows which will hardly make any impression at all. If we examine the plate after this exposure is made, there will be no apparent change in it. But if we put the plate in a photographic developer we find that in a short time the image as described before will slowly make its appearance. The parts affected by light have been reduced to metallic silver. But it is not yet a negative. If we examine the film after development we will notice that the shadows or weaker parts of the image still possess a creamy-like appearance like the whole plate had before it was developed. This we must remove by fixing, which is done by immersing the plate in a solution of hypo, or more properly, thiosulphate of soda, which dissolves out the unaffected silver salts that gave the creamy appearance to the plate. The plate is now in all respects, a negative, except that all traces of hypo must be removed by washing. It is then hung up to dry.
This image does not necessarily have to be projected by a lens. If we could imagine a pinhole about 1/1500 of an inch in diameter that would admit plenty of light as well, we would have a perfect lens of any focal length, and a covering power nearly up to 180 degrees. Incidentally, pin holes up to 1/20 of an inch are sometimes used with very pleasing results.
We all know how light rays can be bent through a prism. The ordinary double convex lens is nothing but a series of an infinite number of such prisms. If the surfaces are cut to perfect spheres, the light rays will cross, or come to a focus, a certain distance from the lens, depending on the radius of the curved surfaces and the refractive index of the glass used. The trouble with this lens is that all of the light rays will not cross or come to a focus at the same point. The blues will not converge at the same place with the reds. The main fault with this lens is color or chromatic abberation, although it still suffers from many others.
This fault is removed by the so-called achromatic or meniscus achromatic lens found on the cheaper cameras by combining two different lenses, and cementing them together. This lens has very little speed or light admitting power. And besides this, it will project a square shaped image in a barrel or pincushion form on the plate depending on whether the diaphragm is in front or behind it. This is known as curvilinear distortion. It can be removed by combining two lenses of this type opposing each other with the diaphragm between, which gives us the so-called rectilinear or rapid rectilinear lens. This lens is hard to surpass as an all round pictorial lens, and is usually supplied in speeds up to F8. It still has its faults, technically. It has not the needle definition of the anastigmat. It has a saucer shaped field, i.e., objects in focus in the center of the plate will not be in focus at the edges or corners; and it sometimes has astigmatism. Also, its covering power is limited.
The good anastigmat lens is supposed to be free from all the foregoing optical defects. It has remarkable definition -- too much in fact. It gives a flat field, is corrected for color, and besides, has more speed. It is an outgrowth of the discovery that glass of different composition has a different refractive index. Quartz glass will not bend the light rays the same as crown and flint glass. By combining lenses made of the different glasses and properly setting them together we get the modern anastigmat. They are made ever many different formulas and are necessarily expensive. The best I have found are the Carl Ziess Tessar, the Bausch & Lomb Tessar, and the Goertz Dagor. It is also a fact worth remembering that the slower anastigmats are the freest from optical defects, i.e., these working at F 6.3 and F.77 have more covering power and cut sharper than those working at F 4.5 and F 2.9, etc.
This brings us down to the important meaning of the diaphragm markings found on every good lens. That do we mean when we say we have an F 4.5 lens? It means that the lens works at F 4.5 when the diaphragm is wide open. What does this mean? It means that when the lens is focussed on some distant object or infinity, the diameter of the diaphragm opening is 1 over 4.5 or 2/9 of distance from the lens to the plate. What good is it to know this? It indicates that F 4.5 represents the angle subtended by the diaphragm when it is wide open, or in other words, gives us a clue to the amount of light that will pass through it. Some system of marking the diaphragm stops had to be adopted by the lens manufacturers in order for everybody to compare the speed of any lens with another, and to be able to use any lens. If you stop any lens down to 11, 16 or 22, they are all supposed to admit the same amount of light at that particular opening, irrespective of make or size. This is very important in figuring exposures. There must be some standard of comparison, otherwise it would be impossible to take out a battery of different lenses and use them with any degree of accuracy. It might be well here to say that the light admitting power of these diaphragm stops can be compared, one with the other, inversely as the squares of the numbers themselves. That is to say that F 8 passes twice as much light or is twice as fast as F 11, which in turn is twice as fast as F 16 and so on down the line to the end, which is usually F 45 or 64. Now supposing we figure our exposure should be 1/50 of a second at F 8, you can see that the plate will be hit with exactly the same amount of light if we stop the diaphragm down to F 11 and give it 1/25 of a second. Here we must do some figuring. If we stop it down one more, to F 16, we must increase the exposure to 1/12 or 1/10 of a second. We cannot hold the camera in the hand at such a slow shutter speed without the danger of vibration, which will ruin the picture. To overcome this we must resort to a tripod or rigid support together with a cable release, It is oftimes necessary in pictorial work, especially when filters are used, to give an exposure of from three to ten seconds. This is where the graflex and kodak usually fall down. They are essentially hand and speed cameras and should be used as such.
What is the advantage of stopping a lens down, under its maximum speed? If my lens works at F 4.5, why not always use it at F 4.5? I can stop a tennis ball at F 4.5 in good sunlight in 1/1000 of a second. The tennis ball will be in sharp focus, but everything on the near or far side of it will be fuzzy or out of focus. I have speed and have stopped fast motion, but I have sacrificed depth in my picture. If one were photographing a field of flowers he would have a different problem. You want the flowers near to the camera as well as those further away to be in sharp focus. This is accomplished by stopping down the lens, sometimes to 32 or 45. Your lens passes very little light at these openings, so you can't stop motion. And be careful that motion stops and the wind is not blowing, or you'll blur your picture. Any ordinary kodak below post card size set at 25 feet, diaphragm at 32, will give almost universal focus. In this connection, it is well to state that the depth increases as the focal length of the lens decreases. It is the main reason why such marvelous effects are obtained with the small motion picture lenses. These diaphragm markings and their use should be thoroughly understood before taking up photography at all.
One of the best all round cameras is the 5 x 7 or 4 x 5 or 3-1/4 x 4-1/4 view with a rigid tripod. I mean by this that more results can be accomplished with this type of camera than any other, but I would not care to carry one to the top of Mt. Rainier or across the Grand Canyon. A good portable kodak of 3-1/4x4-1/4 size would be better for this. The Graflex is too heavy, also, and its use is too restricted. For wild animal photographs it is indispensible. It would be well for us all to adopt the 3-1/4x4-1/4 size, because it makes a fair sized print; because it will stand enlargement up to 8 x 10 or 11 x 14", and last but not least, because the subject matter on a negative this size can usually be printed on a lantern slide by contact. It is economical, and the lens equipment small enough to insure a high percentage of good results.
I do not advise the use of film packs or glass plates. Use either roll film, or preferably, cut film. The advantage of cut film is the variety of emulsions now available, such as commercial ortho, par speed, super speed, commercial panchromatic and portrait panchromatic. I would suggest that we adopt this size 3-1/4x4-1/4. right now, for the use of field naturalists. The type of camera can be decided upon by the individual who uses it. From what I can gather, Yeager, Ruhle and Collins could get along very well with a graflex, while Brockman, McKee, Been and Harwell should have a more portable camera for climbing. A graflex is always handy to have around if you cam afford one. Been and Harwell, I know, could use one to advantage.
Now a word about composition. The best suggestion I can make is for you to study pictures and get in the habit of seeing pictures. You fellows are living in the most beautiful parts of our country. You have pictures almost anywhere you look. If you haven't already adopted photography as a hobby it is because there must be a screw loose somewhere. A camera in any one of our national parks should soon pay for itself.
Perhaps, without knowing why, our attention is oftimes attracted and held by a picture. It may be the composition of color that pleases us, or the composition in line and mass. In photography we must see our picture in black and white. We therefore look for line and mass. These must hold us within the picture area and not lead off somewhere else. The lines should always lead the eye to the center of interest. This is not always easy or always possible in photography. The artist can place things where he will and thus has the bulge on us. Have your people or animals moving or facing into the picture and not off of it. Watch the way the animal stands, the position of the head and ears. Look for catch lights in the eyes. All these things are done every day. In photographing groups or individual persons, do not have them face the sun directly. Have them turn a little to one side so as to get one highlight on the opposite cheek. In photographing forests and mountain ranges, have the sun to one side so as to throw them into high relief.
Filters and color sensitive (panchromatic) films are usually necessary to photograph clouds, distant objects, and snow capped mountains against the sky. The ordinary film can render these only at very high elevations in clear weather. The filters most in use for this purpose are the K1, K2, K3, and G. Wratten Filters. When you get a box of panchromatic films the factor or multiplication numbers for the increase in exposure for these filters is printed on a card inside.
Get a good exposure meter or guide, to determine your exposures. The Eastman Kodak Company will be glad to furnish free of charge pamphlets describing in detail nearly every photographic activity. If you are interested, send for the whole set.
There are a million things I haven't touched upon. have to figure them out for yourself. You'll just have to figure them out for yourself.
Dark room work is fully explained in every box of plates, paper, and chemical sold. All you need is practice. To make it easier still, prepared developer and fixing powders are furnished. All you do is to add water. In printing it is well to remember that the paper must be fully developed out. That requires from 45 seconds to 1-1/2 minutes. If the image comes up too fast in the developer, and you have to take it out before time, it is because you've given the paper too much light. Throw it away and try another.
It is a wise practice to use only the developer formular recommended for the particular brand of paper or films you are using.
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