"4X5" means that the film comes in sheets (rather than rolls), four inches by five inches. Because this is so much larger than 35mm film (which is about 1X1 1/2 inches), it isn't necessary to enlarge the image as much to create a print of a certain size. Also, the larger film area is able to capture more image "information," just as you can write more on a large piece of paper than you can on a small one. This adds up to sharper images.  Even at an image size of 23X29 inches, the detail is stunning (see illustration on "Technical Details" page).

"4X5" is generally considered the smallest "large format" film.  8X10 and larger sizes are also used, but they are proportionately more cumbersome, and would limit my mobility in the field.

A "technical field camera" is a type of view camera.  It is of metal construction, consisting of a rear box that holds the ground glass for focusing (the image is upside-down) and the film holder; a front frame that holds the lens; a bed with rails for moving the lens forward and back to focus the image, and a bellows between the rear box and the front frame, to keep the light out and provide flexibility to adjust the lens and rear box. The field camera has less adjustability (next paragraph) than typical studio cameras, in return for advantages in size and weight -- field conditions seldom require the degree of adjustment available in studio cameras, and the field camera easily folds up into a compact, well-protected package.

Besides the large film, this type of camera allows a level of control over the image that most cameras can't muster. For example, the lens is mounted to a board that can be tilted up or down within the front frame. While most cameras focus onto a plane parallel to the film, this adjustment allows the plane of focus to be adjusted to any angle (e.g., down onto the surface of a pond, so that everything from near to far is in perfect focus, even without "stopping down" the aperture of the lens to increase the depth of field).

There are a number of good books on the subject of large format photography. I would recommend Using the View Camera by Steve Simmons. Simmons also publishes View Camera magazine; information is available on their website: www.viewcamera.com. If Simmons' book is unavailable, I'd suggest Large-Format Photography (Kodak Publication #O-18E); other books are available.