In light of Dingus's discovery we can better understand the power of O'Sullivan's apparently artless frontier photographs. The most striking thing about them is the similarity in the way they look; they possess a simplicity, honesty, directness, and focus familiar from the Civil War photographs. The feeling of honesty and directness comes from a use of focus with a great depth of field, but one that also, in the tradition of impressionsim, approximates human vision; the images are sharp and detailed but not the landscapes of Ansel Adams with a tremendous depth of focus in which every part and distance of the scene is clearly seen. The focus, simplicity, and directness come from O'Sullivan's use of the limitations of his frame. From the complexity of three dimensions, he chooses one perspective from which to view the scene. Furthermore, he consistently emphasizes one or two aspects of the scene, expressing the essential impressions that it gives. Thus, O'Sullivan's technique approximates human experience of landscape just as the style of his photographs approximate human vision.
For example, in "Tufa Rocks, Pyramid Lake (Nevada)" O'Sullivan waited for the right light that allowed him to emphasize detailed texture as well as the great size and undulating form of the rocks. The humans provide a scale by which we can identify the subject for what it is. The emphasis is on texture, size, and form. The presence of humans and the implication of size also emphasize the novelty of the rocks with a touch of humor. "Canon of the Snake River (Idaho)" isolates one portion of the canyon wall, and emphasizes its shape through the vantage point and contrast of light and shadow on its faces. Yet, O'Sullivan maintains balance in the composition with the curved line of the river, its gesture of movement and suggestion of distance. The light and shadow and the line of the river make this piece a sophisticated and effective portrayal of negative and positive space.
"South side of Inscription Rock" is a wonderfully assertive statement of the subject. It fills the frame with a towering and upwardly thrusting presence. Little else fills the frame but the sky, which provides a contrast for the shape, texture, and tone of the rock, emphasizing the strength of its presence by its own flatness. The effectiveness of O'Sullivan's composition is reiterated by a comparison with Alexander Gardner's view of the same form which lacks the tension and powerful presence of O'Sullivan's view. The light and shadow subtly define the form and texture of the rock, and highlight the vertical lines in the rock which add to the suggestion of height. The presence of a man in the foreground is incidental if not practically invisible. Yet, if noticed, he provides the perspective from which we may gain an absurd sense of scale, endowing the rock with grandeur and perhaps even indifference. A sharp focus and subtle use of light make for a convincing expression of the rock's awe-inspiring presence activated by the distance and height from which the photograph was taken.
Two images of "Canyon de Chelly, New Mexico," portray the overwhelming presence of rock formations as "South side of Inscription Rock" does. The also portray space between the winding walls of the canyon. The seemingly overlapping pattern of the canyon walls and the contrast between shadow and light portray the shape of the foremost rock structures and the depth of the scene behind them. A careful comparison of the two versions shows that O'Sullivan has tilted his camera in the second one, making it appear that the foremost rock structures are leaning menacingly toward the tiny camp ground on the left. With the canyon wall in the front and on the left also tilted, the canyon seems less like a corridoor and more spacious. The first view emphasizes the stability and order of the scene, while the second depicts its discomfiting size and strangeness.
"Host sulphur spring, Ruby Valley, Nevada" also expresses the strangeness of the landscape. It describes the sulphur with the detail of its texture and the whiteness of its color. The strangeness of it is self-evident but also emphasized by the contrast between its whiteness and the figure's blackness. The figure, himself, is strange, appearing as black as he does, and this contributes to the overall impression. The scene is also calm. The grass and sulphur, water, mountain ridge, and sky create parallel horizontal lines that give the picture stasis. At the same time, the curve in the water keeps the image from being dull.
"Sand dunes, Carson Desert, Nevada" expresses a mixture of loneliness and beauty through contrast. O'Sullivan has selected a few peaks of sand to focus upon. He expresses the delicate beauty of their form by contrasting the organic line of their silhouette with the straight and diagonal lines created by the sage brush on the ground, the mules and wagon, and the tracks left in the sand. He also contrasts the lightness of the sand with the darkness of mules, wagon and brush, and the hint of mountains framing the peaks of sand. The contrast sets off the beauty of the sand peaks and also the isolation of the wagon and mules.
In general, his photographs evince an interest in depicting space and distance, size, texture, shape, and form through the subtle use of light, line, detail, and contrast.
O'Sullivan's choice of emphasis seems to have determined the perspective, yet at the same time, the frame provides the limitation necessary to create the emphasis. His compositions fill but do not swell the frame, in an unequivocal statement of the subject and expression of its essence.
It is as if confronted with a new, exceptionally physical vastness, O'Sullivan had to fine tune his technique, perceiving and portraying his subject with even more focus and clarity. As in his Civil War photographs, an original composition and attention to formal elements allows O'Sullivan to portray time and distance, to create mood, and suggest truthfulness. The compositional technique O'Sullivan had developed during the war furnished him, perhaps more than any other frontier photographer, with the understanding and interest in space necessary to deal with the complexity of the space of the western frontier as Adams describes it. Perhaps that is why he never apparently felt the desire to make use of the picturesque tradition that made for aesthetic and elevating pieces of art rather than records of scenes in space and moments in time.