Medium format cameras use 120 or 220 roll film, which is about 6 centimeters wide (2 and 1/4 inches). This size of roll film was introduced in 1898 by Kodak for its Folding Pocket KODAK Camera. It thus seems safe to say that the world has reached agreement on the proper height for a medium-format negative. On the other hand, nobody has ever agreed on the proper width. There are many standard widths for 120 camera frames: 645, 6×6, 6×7, 6×8, 6×9, 6×12, and 6×17. These numbers are ostensibly in centimeters although in practice a 6×6 camera such as a Hasselblad will expose a 56 x 56 mm frame.

thus for a rectangle (6×4.5), a 6×6 or 6×4.5 camera will produce 56mm x 41.5mm = 2324 sq mm, while a 6×7 camera 56mm x 69.5mm = 3892 sq mm and thus is nearly 1.7x the area (by comparison 6×4.5 is 2.7x the area of 35mm film which is 36x24mm =  864 sq.mm)

many film photographers feel that a 6×6 camera can be printed well to 16“x16”, but larger prints start to lose the creamy tonality. Likewise a 6×7 or 6×9 can print to 16“x20” for the same quality as a 6×6 printed to 16“x16”.

note that the future of medium format is likely to be 6×4.5 digital backs (even if using a 6×7 medium format)

The 645 format is the smallest, lightest, and cheapest roll-film design. Negatives are a little squatter than the standard 35mm frame (24x36mm) and therefore full-frame printing on standard paper sizes such as 8×10 need not require a cropping decision. What you get is a sharper deeper negative that enlarges beyond 11×14 with more grace and is easier to handle if you do your own darkroom work. It is also more expensive and difficult to scan than a 35mm neg, so keep that in mind.

Mamiya pioneered the 645SLR system camera in 1975.

Fuji has done great things to promote this format. They make 645 lenses that are just as good as Hasselblad's 6×6 lenses. They charge less than half the price. Then they throw in a perfectly good body behind the lens for free! Sometimes Fuji puts a meter in the body, something that apparently costs 'Blad about $5,000 extra. Sometimes Fuji puts in an autofocus mechanism (they were the first to do so in the medium-format world). Sometimes Fuji adds a wide-to-normal zoom lens! Whatever they do, the integrated camera, body, meter, and lens costs about as much as a Hasselblad or Rollei film back.

The Bronica RF645 was the latest design 645 film camera and is more ergonomic, lighter and has AE and Program mode auto-exposure with 45mm, 65mm and 100mm lens options

discontinued in 2004; Bronica has been taken over by Tamron and the future of these cameras seems limited as repairs and support by Tamron ceased in 2016;

see Mamiya / Phase One 645 medium format camera system

Hasselblad H series autofocus cameras (2001)

see dantestella.com

lightweight, compact (for medium format), plastic, easy to use with sharp lenses but few manual controls and requires batteries

bright, polarised portrait aspect 4:3 ratio viewfinder has parallax-corrected projected framelines

shutter is an electronic (stepper-motor-driven) #00 that has manual settings up to 1/500 sec

i versions add 2nd shutter release and Fujifilm film barcode reader to auto set film speed

metering through the viewfinder is said to be quite accurate

relatively noisy but quite fast 900-step autofocusing system with AF lock which also locks exposure

no manual focus focusing aids! Must use zone focusing - ie set it to a given distance and allow DOF to address focus

no exposure lock switch

built-in flash plus hot-shoe

lens retracts into the body

AF mechanism may require costly calibration if at all still possible - check sharpness on a roll of film before you buy one!

close focus restrictions can be an issue for some

45mm f/4 wide angle lens = 24mm fov on a 35mm system

i version adds 2nd shutter release and Fujifilm film barcode reader to auto set film speed

60mm /f4 lens = 35mm fov on a 35mm system

version 1

version 2 increases the number of shots on 120 film to 16 (from 15) and the number on 220 to 32 (from 30), adds a little protective ridge around the AF button to prevent accidental pressing, and quiets down the focusing

i version

55-90mm f/4.5-6.9 zoom lens = 30-50mm fov on a 35mm system

has a range of improvements and changes in control layouts

12exp. per 120 roll

Lenses project circular image disks. If you park a rectangular section of film behind the lens, you're wasting much of this “circle of good definition”. If you expose circular frames of film, you're wasting much of the film. If you expose square frames of film that fit exactly inside the image circle, you're not wasting any film and you're wasting as little image circle as possible. Thus the lenses for a Hasselblad (6×6) are much lighter than the lenses for any 6×7 camera. If you're going to suffer with the weight of medium-format lenses, then you should at least put film underneath as much of their image circle as possible, something that only a square format does. However, digital backs will only be 6×4.5cm and if you print to 8“x10” from 6×6 negatives the you are forced to crop.

If you're rich and strong, try the Rollei 6008 single-lens reflex system. If you are travelling and want something light, the Mamiya 6 rangefinder system is wonderful. If you're poor, you might consider a twin-lens reflex such as the Yashica 124 or Mamiya.

see Hasselblad

see Bronica SQ system for more details

discontinued in 2004;

see http://medfmt.8k.com/mf/g6x7.html 

10 images per 120 roll; traditionally the standard size for stock image photography;

Photographers on portrait assignment for magazines often use the 6×7 format. The weight isn't a problem since they have assistants, rolling carts, and advance planning.

If you want a lighter kit, your only real options are the Fuji rangefinders (very cheap but no meter) and Mamiya 7 rangefinder (meter in the body and interchangeable lenses including a delicious super-wide lens). 

If you want to pretend to be a magazine portrait photographer, invest in the unbelievably heavy and clunky Mamiya 6x7 medium format SLR camera system

If you want to pretend to be a starving artistic nature photographer, throw a Pentax 6×7 II system into your beat-up full-size van. This is a huge 4-pound SLR body that includes a prism the result is what looks like an old Nikon on steroids. Lenses are sensibly priced.

All in all, your choice really depends on what you want and what you need. If you shoot with superwides, the Pentax 45m or Mamiya 7 43mm are the widest (by 5 and 7 mm's). If you shoot fill flash, the 7, Plaubel, Rz and GS1 (the GS1 has TTL flash as well) all have meter coupled leaf lenses. If you shoot studio, the Rz and GS1 have 'normal' interchangeable polabacks (the RZ has a far wider lens range). If you shoot sports, the Pentax 67 has a 1/1000th shutter setting and hyperfast ED teles.

with the exception of the RZ, there isn't a camera here that couldn't stand a heavy improvement. Even the newly introduced Mamiya 7 *needs* closer focus ability and faster lens options (a Mam.7 100-110 mm option will be nice as well); in the face of that, any choice here is going to be a compromise.

“standard lens” is 90mm.

currently, the biggest digital back sensor for the 6×7 is only just under 645…makes the 50mm wide angle on the RZ not so wide

see Mamiya 6x7 medium format SLR camera system

discontinued in 2004; uses Zenzanon PG series of lenses.

On the test front, its lenses are consistently great (especially the 100 3.5 which handily *killed* the competition in Foto magizin's tests)  and the comments that I've heard from users bear that out. In the size dept., it's design is very definitely H'bladesque; it's small enough, but it's a little strange to use vertically as is (to me 'as is' means w/ a prism but without the grip).

If you add the speed grip, the convenience factor goes up enormously but the camera gets to be quite a handful. If you're going to be street shooting with this camera, you're going to need the grip;  with the grip, the camera is just too noticeable (Very sore thumb time). Then again, if you're using fill flash on an SLR, the GS1 is a lot easier to handle handheld (in full AE prismed regailia), than the RZ is and its the only 67 to offer TTL auto flash.

The GS1 lenses could focus closer and are the slowest of the contenders (bar the Mam7), still,  it's the best available execution of a 'do everything' ideal in 67 SLR'dom. The GS1's greatest strengths are that it's reasonably small and light, it's completely modular (w/interchangeable backs), it's well built and reliable, has ISO databus connection between each back and the prism and is well automated with the AE rotary prism (spot option) or the easier to use and far smaller AE prism.

This camera is designed as a field camera, for handheld SLR convenience (convenience is only relative with this camera). The camera remains basically unchanged from its original form and, having been intro'd about thirty years ago (and based on the design of the Pentax Spotmatic 35mm camera), almost every feature is archaic by modern standards. It's very large and heavy (by 35mm standards; small and light by 67 standards), fires off like a canon (Mucho vibration and noise) and is quirky like the Ptx 645 (If you take off the TTL prism, then replace it, you've got to remove and replace the lens before you get a reading back. The meter just goes dead). Some lenses focus very closely (55, 90, 135 and new 200), others don't focus closely at all (300/4 and the old 200).

Working with the camera is an exercise in indecisive relativity; it charms you with its fast lenses, its tanklike craftsmanship and its versatility, but bothers you with its noisy, vibratory release and its 'retro' feature set.

Viewing through the normal focus screen is dark and fairly coarse but is extremely contrasty. Beattie and britescreens are thought of by many as required upgrades because of this, though I find the standard screen easier to focus.  The Pentax offers the only 67 slr instant return mirror.

great to shoot, very fagile and pretty unreliable.

to shoot it commercially you need two bodies, one for film and one with an NPC Pol back

digital back is not possible.

I've read that Astrophotographers prefer the Ptx.67 because of its straight line film path and resulting superior flatness but the side gate rollers push the film edges away from the film plane. An easy fix is to cut match cardboard into small pieces and insert them in front of (under) the spring tabs.

Imacon have a digital back adapter for the GX680 see FlexframeSolutions.pdf 

6×9 format is same aspect ratio (3:2) but 5x size of 35mm film format. 8 images per 120 roll;

6×12 is a panoramic format is the largest format of roll film that will fit into a standard 4×5 enlarger. If you use larger formats, you'll be limited to contact prints, digital imaging, or professional photo labs.

With a rotating lens on a 612 camera body, you can get some very interesting photos. 

The Noblex is the most common example of the breed, producing a 146-degree photo free of distortion and light falloff.

you can get 6×12 roll film backs for 4×5 large format cameras.

4 images per 120 roll; big, heavy and bulky; requires a 5“x7” enlarger to print;

Scale focus is the only means of focusing a 617 camera; there is no built-in rangefinder and no way of viewing through the lens to focus

a 210mm focal length covers about same angle of view as a 50mm on a 35mm camera.

generally shoot at f/22 or f/45

see large format

<>If you already own a 4×5 view camera, a cheap way to get into 6×12 is with a roll-film back. You're saved the hassle of loading film holders but the other operational annoyances of the view camera will still slow you down. On the plus side, even with the very cheapest view camera and 6×12 back you get perspective control.