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Understanding Medium Format

This article was originally written with reference to film-based cameras. The same factors apply in terms of image quality though with regard to digital. The only significant difference is price, with medium format digital currently (2003/2004) commanding a considerable premium.

The Goldilocks of Formats

The 1980's saw the victory of 35mm. Many factors converged, making 35mm and in particularly SLR cameras the primary choice of both amateurs and professional photographers. Better films was one of these factors. Finer grain and higher resolution allowed the use of the much smaller film format for more demanding applications, and when combined with smaller camera and lens size, longer film loads, ease of use and usually greater versatility the arguments were compelling. 

But medium format never lost its allure, just as large format didn't for many.

While most pros understand the need for medium format in many situations, amateurs and newcomers to photography can find the subject confusing, and the array of choices available bewildering. Leaf shutters Vs. focal plane shutters, interchangeable backs, format differences, 120 Vs 220 film — all of these are unfamiliar to someone who just works in 35mm.

This tutorial is therefore devoted to explaining the jargon that's unique to medium format, some of the major difference with 35mm, and takes a brief overview of the model choices available. At the end of this page there are links to camera reviews on this site and elsewhere as well as other pertinent web links for those that would like to explore this topic further.

Photographed with a Mamiya 7 II and 65mm f/4 lens on Provia 100F

Why Bother?

35mm cameras are wonderful. They feature every technological advance available, from autofocus to 8FPS motor drives. Lens choices range from 12mm Ultrawides at one end to 1000mm super telephotos at the other. Lens speeds are as fast as F/1.0 and cameras can be small enough to fit in ones pocket or robust enough to use in combat conditions. Why would anyone want anything more?

Image quality! As convenient and enjoyable as 35mm camera systems are there is a limit to how large a print one can make. Many, myself included, feel that 11X14" or 11X17" (A3) is the largest print that still retains acceptable quality. This is regardless of camera or lens used. It's just an inherent limitation of working with such a small piece of film. (Please don't write telling me about the wonderful 20X24" prints that you've made with your Watziflex and its Lumifast lenses. I don't want to hear about it :-)

On the other hand images shot on medium format can typically be enlarged to 20X24" with little problem. Even in smaller prints the image quality advantage of medium format isn't subtle, it jumps right out at you.

Many 35mm photographers, in their search for higher image quality change from Nikon to Canon, from Canon to Contax, from Contax to Leica, believing that some other brand will give them sharper, higher quality images. Regrettably, the improvements of switching from one brand to the other are mostly illusionary. Sure there are some differences, but nothing like the one that comes from stepping up to medium format.

Finally, remember that the remarkable improvements to film emulsions that have taken place over the past 25 years apply equally to medium format. The quality gap remains.

Tumbleweed Dunes, 2000

Photographed with a Rollei 6008 and 40mm Schneider Super-Angulon Lens on Fuji Provia 100F

Film

Medium format means 120 and 220 size roll film. Each is sold in individual boxes or in five-packs. In either case individual rolls come wrapped in a sealed foil pouch which is torn open to get to the film. The film is on a spool rather than a cassette, and the spool is sealed closed with a piece of glued paper. This piece of paper is torn off and the film unrolled slightly to thread onto the camera or film back's take-up spool. When the film is finished, the finished feed spool is switched to the other side and then used as the new take-up spool. (Roll film creates a lot of litter). 

Just about every emulsion from the major film companies is available in 120 film. Most are available in 220 as well. The difference between 120 and 220 film is that 220 is twice as long and therefore holds twice as many images as 120. The spool sizes are the same. What differs is that 120 film has a paper backing that runs the full length of the film. 220 film only has a paper leader. Thus more film can be wound in the same space with 220.

The reason for the paper backing on 120 film is historical. Roll film cameras used to have a small transparent ruby window on the back that allowed you to see the frame number so that you could wind the film to the next frame. Modern cameras don't have this anymore, but the film still does. Even the frame numbers are still there on the paper backing.

Some cameras (like the Mamiya 7 and Pentax 67) can take either 120 or 220 film. All that's necessary is to move the pressure plate to a new position. The frame counter will count the correct number of frames. The reason for changing the pressure plate is because 220 film is thinner than 120 film due to the lack of paper backing.

Other cameras — those with interchangeable backs like the Hasselblad or the Rollei 6008, require that you use different backs for either 120 or 220 film. This is a nuisance and expensive.  You basically decide which film type you prefer and then have to stick with it.

Formats

While 35mm film is essentially a fixed size format (24X36mm — the Hasselblad XPan and other panoramic cameras being exceptions), roll film can be used for a number of different frame widths and thus formats. Since the film is fixed at 6cm in width what varies is the length. The most common formats are — 645, 6X6, 6X7. Lets look at each.

645 is 6cm X 4.5cm. This is a rectangle that is very close in proportion to the 8X10" print format and will enlarge to this format with very little cropping needed. The most popular cameras in this size are the Mamiya 645, the Pentax 645, Bronica 645 and the Contax 645. These cameras are the most like 35mm cameras in size and handling. Most now offer autofocus and extensive automation. They are the smallest SLRs that use roll film.

I feel that the slightly greater bulk of a 6X6 camera is usually a worthwhile compromise because it obviates the need to rotate the camera between horizontal and vertical framings. Also, some models (particularly folding cameras), frame vertically when held normally. If you're a portrait photographer or shoot a lot of weddings this may not be an issue. But for someone that shoots landscape and nature it can be annoying. Check the camera that you're interested in to see if this is the case.  645 cameras get 15 or 16 frames to a roll of 120 film. 

6X6 is the most popular roll film format. Why is this? Part of the reason is that this square contains both a vertical and a horizontal composition on the same frame. A 6X6 image is composed of a vertical 6X4.5 and a horizontal 6X4.5. No need to rotate the camera. No need to rotate the film back. Just take one shot and get both compositions. Some people, myself included, also find a square image very appropriate for some subjects. One gets 12 frames to a roll of 120.

The various Hasselblad and Rollei 6008 models are the most popular SLR cameras using this format. In North America Hasselblad is the market leader. In some countries of Europe and Asia, Rollei is. Bronica is a smaller though long-time player as well.

Dune Trees — October, 2001

Photographed with a Hasselblad ArcBody and 35mm Rodenstock lens on Provia 100F.

6X7 is very popular for several reasons. Like 645 the format it enlarges to an 8X10" print with little cropping. Though only slightly larger than 6X6. There are four popular cameras offering this format; the Mamiya 7II, the Pentax 67II and the Mamiya RB & RZ67. The Bronica GS1 is also a contender.

The Mamiya is a rangefinder camera; very much like an M Leica on steroids. The Pentax in turn is like an overgrown 35mm SLR. Both of these are excellent field cameras. Neither has interchangeable film backs. The Mamiya RB and RZ67 models are similar to the Hasselblad in configuration, have interchangeable finders, viewfinders and backs. Because the film format is rectangular the RB and RZ backs rotate, providing vertical and horizontal framing, eliminating the need to rotate the camera. One gets 10 frames to a roll of 120 with this format, and either 20 or 21 frames on 220 film, depending on the camera.

Interchangeable Backs

One of the advantages of a number of models of medium format cameras is that they offer interchangeable film backs. Pop off a back containing colour film and replace it with a roll of B&W film in just a few seconds. Have multiple backs loaded and keep shooting quickly when the light or the subject is changing fast. Assistants to pros are always loading backs so that the photographer never has to pause during a hot shooting session.

Some cameras only allow film inserts to be replaced. This permits having fresh inserts pre-loaded with film, but not changing film types in the middle of a roll.

Most medium format cameras use a dark slide to allow backs to be removed. This is a small metal shim that blocks the light from striking the film and allows the back to be removed. The Rollei 6008 uniquely has a laminar dark slide. This is somewhat like a Venetian blind. It rolls up and covers the film thus eliminating the problem of lost or sat-on dark slides.

Be aware that loading and unloading roll film is a slower process than with today's rapid-loading 35mm bodies. It can be a bit of an art, especially with some cameras, but once mastered becomes remarkably quick and intuitive.

Prisms and Waist-Level Finders

Many of the top medium format cameras have interchangeable viewfinders. This means that a waist-level finder can be used and then switched to a prism finder for eye-level use. Some prism finders' feature built-in metering capability for use with camera bodies that don't have built-in meters. 

Various levels of exposure automation are available. Some aperture priority, some shutter priority and some full program automation. Several manufacturers, like Rollei and Hasselblad, offer 45 degree prisms as well as 90 degrees. This allows looking into the viewfinder at slightly below eye level. Some photographers prefer this.

Metering varies as well from simple averaging to matrix and spot metering — just as with 35mm SLRs.

As for waist-level finders, they allow you to look down onto the groundglass, seeing the whole image with both eyes. This is a great way to compose a portrait or a landscape shot because it's much like looking at a finished image.  A waist-level finder also allows you to comfortably position the camera low and close to the ground. These also have a pop-up magnifier to aid in focusing. And, unlike prism finders, waist-level finders are small and fold flat, and therefore significantly reduce the size and weight of a medium format camera.

Though available for most 645 and 6X6 cameras, they make the most sense for square 6X6 cameras. On the others one is limited to either a vertical (645) or horizontal composition. Looking sideways into a waist-level finder isn't very comfortable.

Focal Plane & Leaf Shutters

35mm cameras today all have focal plane shutters. These move either horizontally or vertically and are located (where else?) just in front of the film focal plane. Medium format cameras have either focal plane shutters, or leaf shutters. Leaf shutters are located inside each lens and open and close like an iris. Focal plane shutters open either horizontally or vertically across the width or length of the film. There are pros and cons to each solution.

Using leaf shutters mean that each lens has to have its own shutter. This adds to overall system cost. The advantage of a leaf shutter is that it will sync with flash at all shutter speeds. Another advantage is that they are small and therefore free of vibration. This is particularly important when using very long lenses. They are also very quiet in operation. 

Focal plane shutters in such large cameras are.... drum roll please... large. This means that flash sync speed is slow (only 1/30th second with the Pentax 67) and they can also cause blur-producing vibration at slow shutter speeds when a lightweight tripod is used along with a long lens. They tend to be noisy as well.

Photographed with a Rollei 6008 and 300mm Schneider lens on Provia 100F

Lens Factors

Photographers who have grown into their craft in 35mm are very familiar with 35mm focal lengths and their coverage. When confronted with medium format they get confused as to what the equivalent focal lengths are. Here is a site that allows you to calculate the equivalent focal length for any format. Here is another.

What you'll see is that you need to use a factor of about .6X to convert for 6X6cm and 645cm, and .5X for 6X7cm. In other words, a 100mm lens on a 6X7cm camera has a field of view similar to that of a 50mm lens on a 35mm camera. An 80mm lens is similarly "normal" on a 6X6cm camera.

One thing to keep in mind is that medium format camera lenses are typically a stop slower than their 35mm equivalents. This is to keep the size down.

Winders and Motor Drives

Like their 35mm brethren many medium format cameras have either built-in or accessory motor winders. Unlike 35mm though don't expect blindingly fast film advance. These are winders, not high speed drives for sports and wildlife shooting. Roll film is bulky and simply won't wind fast enough for this.

Mirror Lock Up

Reflex mirrors on medium format cameras are big — particularly on 6X7cm cameras like the Pentax 67 and Mamiya RB/RZ. Use mirror lock-up on any shots that are less than 1/125 second. In fact, unless absolutely required, use it for all photographs that you can. Mirror vibration can be a real sharpness killer.

Twin Lens Reflexes

Though they don't exist new any longer, for much of the 20th Century twin lens reflexes were extremely popular. The Rolleiflex was the preeminent model for decades and can still be found in excellent condition at used camera stores and swap meets. It is also still is available new as a quite expensive "collectors" model, the GX. At the other end of the spectrum there is the inexpensive Seagull TLRs from China. 

The concept is, instead of having a reflex mirror, as in a SLR design, a second lens is positioned above the shooting lens and the user views the scene though this lens. There are many benefits to this approach. The view is uninterrupted when a shot is taken, as the viewfinder never blacks out. The camera can be made somewhat thinner without a mirror housing. On the other hand TLRs are somewhat taller because of the additional lens, and using polarizers is complicated. Use of dense filters such as those for infrared shooting is facilitated though.

Mamiya made a couple of camera models in their C series (C220 and C330) that had interchangeable twin lens assemblies. They were large and heavy, but reasonably priced. I used one extensively in the 70's when I worked as a photojournalist. I used them mainly for the bit of fashion and industrial work that I got from time to time. They did the job.

Miscellaneous Items

Pressure Plate: Film, whether in a 35mm or a roll film camera, needs to be held absolutely flat, and in the exact position where light from the lens comes into focus. The is called the film plane, and what achieves this is called a pressure plate. It is spring loaded and designed to exert a smooth but strong pressure against the film, pressing it top and bottom against the film rails.

Screens: Most medium format SLRs have interchangeable focusing screens. Particularly with non-autofocus models, having the right focusing screen for the given application is important. Some have microprisms, some are plane ground glass. Others have split image rangefinders. Often they have hatched lines engraved. These are very useful as an aid to composition with certain types of shots, such as in architectural and product photography.

Who's Been Left Out?

In addition to the most popular 645, 6X6 and 6X7 formats there are camera available that offer 6X8, 6X9, 6X12 and 6X17 formats. 6X8 is only offered by the unique Fuji GX680 III. 6X9 is a format that again, Fuji specializes in offering in the specialized GW680 III rangefinder camera and from several makers of roll-film backs for 4X5 cameras.

612 is an interesting double-width format that is available primarily from the Horseman 612, but also as roll film backs for various 4X5" cameras.

617 is available from two makers — Fuji with its GX617 and Linhof with its 617 model. These are really wide, a 3:1 aspect ratio, but boy is the image quality high and the format capable of producing unique and impressive results.

Other Medium Format Links

Hasselblad    Rollei 6008    Contax 645    Mamiya 645   Pentax 645   Hasselblad ArcBody   Pentax 67   Mamiya 67    

Medium Format Digest   More Medium Format Links 

For a look at the medium format systems that I own you may also enjoy reading my other article on Medium Format.

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Concepts: Single-lens reflex camera, Photographic film, Medium format, Photography, Camera, 120 film, Mamiya, Photographic lens

Entities: the Pentax 67, Rollei, Nikon, Canon, Hasselblad, Bronica, North America, Europe, Asia, China, Michael Reichmann, SLRs

Tags: cameras, medium format, 35mm, medium format cameras, roll film, 220 film, focal plane shutters, image, 120 film, Mamiya, leaf shutter, waist-level finder, image quality, film format, pressure plate, roll film camera, interchangeable film backs, Most medium format, Hasselblad, Rollei, focal length, Pentax, dark slides, equivalent focal length, paper backing, film types, prism finders, popular cameras, roll film format, smaller film format, interchangeable backs, Vs 220 film, mirror, rangefinder camera, size roll film, film focal plane, twin lens, 35mm film, Mamiya RB, format camera lenses