Summary: This article explains what large format photography is about, and weights the advantages and disadvantages of using a large format camera. It also provides references for further information.
What is a Large format camera ?
That's grand-dad's bellows box-like camera, where you had to disappear under a dark cloth. The principle remains the same, however nowadays they have evolved into precise and sophisticated instruments.
With a few notable exceptions, these cameras share the following characteristics:
Large image size: 4x5 inches (10x12cm), the most popular format by far, up to 20x24 inches (the Polaroid camera, which can be rented on-site for a reasonable fee). The film comes in separate sheets rather than rolls, but see below.
Flexible bellows connecting the front and back: they allow the use of a range of focal lengths (with different lenses. there are no zooms in such formats) and focussing distances, as well as providing for lateral adjustments and angular adjustments between film plane and lens plane.
Ground glass viewing: makes it possible to assess the image with great accuracy once you get used to the dimness and inversion.
Interchangeable lenses: you are not limited to a particular mount.
By contrast, Medium format cameras use roll-film which is 6cm wide so that the format available on those cameras are (all in cm) 4.5x6, 6x6, 6x7,6x9,6x12,6x17. Therefore they produce image whose size is less than that produced by large format cameras (hence the name). The vast majority of medium format cameras operate a bit like 35mm cameras ("small format") and in particular don't have features 2,3,4. However, a few medium format cameras share these features, and are also considered on this web site, since they actually operate like large format cameras. On the other hand, with almost all the large format cameras it is possible to use roll-film holders of various sizes and to therefore produce medium-format images.
What are the main benefits of the large format camera ?
Larger image size. Results are sharper, have a better tonality, and are grain-free. A 4x5 has 13 times the area of a 35mm frame. A 5x7 has 25 times that area. Contact printing gives an image whose delicacy cannot be matched by any enlargment, and allow a number of "alternative" processes.
Camera movements. You have more control on the final geometry of the photographed objects and of the perspective as well as on the areas of sharpness.
Individual sheets of film. You can use as many types of film as you like easily, easily, including Polaroid, and process each sheet of film individually for optimum results. The latter point makes it possible to use Ansel Adams Zone System for black and white film.
Contemplative approach. You take your time for each image This is the flip-side of the drawbacks: you spend so much time on a single exposure, and invest so much effort in it that you're compelled to think it through carefully and do it right.
What are the main drawbacks of the large format camera ?
Everything is manual. Most other cameras do some things automatically for us that we take for granted -- like preventing fogged film, double-exposures, non-exposures and so on. You need to remember to do things that were never an issue even with the most manual 35mm camera. As a result, there are more ways to make mistakes than you could ever imagine.
Equipment and film: the equipment is bulky, heavy (a good tripod is necessary) and relatively expensive. The cost per photograph is considerably higher than the same image in smaller format. Think of it as being proportional to the film area.
Larger magnification: longer focals are needed for the same angle of view: The equivalent of a 24mm in 35mm is a 75/90 lens in 4x5, a 120mm lens in 5x7. Depth of field is a serious problem. The cameras movements become *necessary* to put everything in focus, and even though some subjects cannot be focussed entirely. Start thinking f32 where you thought f5.6 ! As a result you often get very long exposures, so wind shake (esp. with vegetation) and reciprocity failure begin to take their toll. Work which requires naturally a high degree of magnification, ie macro and tele-photo, is particularly impractical, the former because of the depth of field limitations, the second because lenses would have to be insanely long.
Everything takes a long time:
loading/unloading your holders at home
moving around your heavy backpack or case and tripod
setting your camera
composing, esp. in low light with slow / wide-angle lenses (f8 max aperture is common)
focussing: tricks are necessary to overcome the depth of field problem
exposing: long exposures are quite common.
It is impractical to photograph quick action or candids, and even in landscape you'll end up missing optimal conditions. Your productivity in terms of number of images (but not necessarily in terms of number of great images) will be very reduced. Think a dozen shots or less when you thought a few rolls. Even though your friends/spouse will complain about the waiting.
Besides, you'll discover by yourself many quirks of Large format photography, like the fact that the dark cloth sometimes tend to fly.
What is the real gain compared to other formats ?
The consensus seems to be that as far as enlargements are concerned, the difference between 4x5 and 35mm is huge, but that the difference between 4x5 and 6x7 will show up only in big enlargements, 16x20 or larger. At 16x20 modern LF lenses have a slight edge due to reduced granularity and high contrast, above that, modern 4x5 wins due to granularity. However, you will see a bigger difference with format for B&W prints than with color prints. On the other hand, a contact print has a special quality that some feel cannot be obtained by an enlargement. Contact printing is also the only way to work with some alternative process such as paladium/platinium, carbon, etc...
Will I have to sell the house ?
Large format photography is actually not that expensive, especially compared to medium format photography (the prices for the 35mm market are influenced by the fact that it is quite consumer-oriented), and a good large format system can be built for no more than a good modern medium format system. There is also possibility to do large format on a budget. A fairly good 4x5 can be bought used for less than $500, and if you are willing to accept some limitations, you can get something which works for a couple hundred of dollars. The latest lenses are indeed very expensive, on the other hand there are a number of older lenses which are really inexpensive, a couple of hundred dollars or less. Most of the lenses will be totally appropriate for B&W work. They don't have to be as sharp as lenses for smaller formats. Modern lenses, which will produce results virtually indistinguishable from the the latest designs, can be bought used for a rather reasonnable price. Since LF systems are usually not submitted to an heavy use like smaller formats, gear which is decades old will usually work fine. A great news is that as you have built a good set of lenses, when you upgrade to a better camera, you just keep them, and maybe change the lensboards. At one point I was hesitating between the Pentax 67 (one of the cheapest MF systems) and 4x5. One of the reasons which got me decided for the 4x5 was that the price of the 4x5 system was a little lower. Film looks expensive too, but you won't shoot as many images as you used to. If you do color, you'll probably have to have your film processed by a lab. The total cost of a 4x5 Velvia (film+processing) is less than $4, the cost of a 5x7 less than $8. On the other hand, B&W film home processed is quite cheap.