Anyone that’s shot a DSLR in a remotely serious manner is aware of the crop factor for APS-C format cameras when compared to their full frame cousins. Nikon and Sony APS-C cameras yield a 1.5x crop factor, while Canon APS-C cameras have a 1.6x crop factor.
And, invariably, if you use the phrase “crop factor,” someone is going to yell at you and tell you that you aren’t cropping anything. However, the term is ubiquitous in identifying the altered field of view caused by using smaller sensors in cameras along with full frame lenses.
We also commonly use the phrase “equivalent focal length” to describe the change in the field of view as captured by an APS-C sensor. For instance, the popular Canon EF 50mm f/1.8 lenses have an 80mm equivalent focal length when used with a Canon Rebel series camera. Of course, most of us understand that this is a misnomer and that the 50mm lens does not change at all to become an 80mm lens when used on a different camera. It is simply that the 50mm lens has a narrower field of view on the Canon Rebel DSLR thanks to the smaller sensor.
Crop Factors on Medium Format Cameras
For those coming from a digital world to test the film waters with medium format cameras, the 35mm crop factor for medium format lenses and film types can be confusing when a 50mm lens can be ultra-wide and a 90mm lens is considered a normal lens.
Below, you will find a crop factor for all of the popular medium format film ratios using 120/220 roll film. These crop factors are based on a diagonal measurement of the negative, so some of the odd ratios may be a little off if you are comparing them purely to the native 2:3 aspect ratio of 35mm film. The goal, however, is to provide a reasonably accurate and consistent measurement in order to identify “equivalent focal lengths” to your full frame lenses that you know by heart.
645 Crop Factor = 0.62
The 645 format frame is 56mm x 41.5mm. It measures 69.7mm diagonally.
The 645 format is the generally the smallest frame size you will see used on 120 roll film. Popular 645 format cameras include the Mamiya M645, 645E, 645 Pro and the 645 AF series; the Pentax 645 and 645N; the Bronica RF645 and ETR models; the Contax 645; the Hasselblad H1 and H2; and the Fujifilm GA645, GS645 and GX645 models.
Popular 645 format lenses and their 35mm equivalents include the following.
|645 Lens||35mm Equivalent|
|80mm (normal angle of view)||50mm|
6 x 6 Crop Factor = 0.55
The 6 x 6 format frame is 56mm x 56mm. It measures 79.2mm diagonally.
As you can easily deduce, the 6 x 6 format is a square format, or a 1:1 ratio. Square photos were cool well before Instagram and remains a very popular format for 120 roll film.
Popular 6 x 6 cameras include the Hasselblad 500 series (aka V System); Bronica SQ series; Mamiya 6 rangefinders and C330 TLR; Rolleiflex 6008 and SL66 models; along with many other used 6 x 6 cameras available at bargain prices today.
Popular 6 x 6 format lenses and their 35mm equivalents include the following.
|6 x 6 Lens||35mm Equivalent|
|80mm (normal angle of view)||44mm|
6 x 7 Crop Factor = 0.5
The 6 x 7 format frame is 56mm x 67mm. It measures 87.3mm diagonally.
The 6 x 7 format is the easiest crop factor to calculate at roughly half the equivalent focal length for full frame cameras. Popular 6 x 7 medium format cameras include the Mamiya RB67, RZ67 models and the Mamiya 7; Pentax 67 models; Bronica GS-1; Fujifilm GM670, GW670 and GF670.
Popular 6 x 7 format lenses and their 35mm equivalents include the following.
|6 x 7 Lens||35mm Equivalent|
|90mm (normal angle of view)||45mm|
6 x 8 Crop Factor = 0.45
The 6 x 8 format frame is 56mm x 77mm. It measures 95.2mm diagonally.
The 6 x 8 format has the same 3:4 aspect ratio found in Micro Four Thirds cameras. Of course, the actual frame size is much large than those compact digital cameras and it is a rarer option for medium format manufacturers. Popular 6 x 8 medium format cameras are pretty much limited to the Fujifilm GX-680, GW680 and GSW680. 6 x 8 format backs are also a somewhat common and easy to find option for the Mamiya RB67.
Popular 6 x 8 format lenses and their 35mm equivalents include the following.
|6 x 8 Lens||35mm Equivalent|
|100mm (GX-680 kit lens)||45mm|
6 x 9 Crop Factor = 0.43
The 6 x 9 format frame is 56mm x 84mm. It measures 101mm diagonally.
The 6 x 9 format has the same aspect ratio of 2:3 found in 35mm film and full frame image sensors. It is about as wide as you see before moving into panoramic cameras, which I’m not covering for the purposes of crop factor comparisons. Popular 6 x 9 medium format cameras include the Fuji GW690, GSW690 and GL690; Mamiya Univeral Press and Voigtlander Bessa.
Popular 6 x 9 format lenses and their 35mm equivalents include the following.
|6 x 9 Lens||35mm Equivalent|
Bobby Stanton says
The issue of crop factor becomes even more convoluted when taking in to account the smaller formats such as micro four-thirds, one inch and the point-and-shoot formats. Why don’t we just express it as an angle of view, calculated for the format and the particular focal length lens in use? This would cover everything from the smallest format to large frame 8x10s. It would be instantly meaningful when considering the scene to be photographed. Everyone would get used to this in time and the problem would be solved.
Try telling that to a director of photography. Although, yea I absolutely agree I think it adds to the mystique.
Williams Khürt Louis says
I disagree :) Field of view is also dependent on the format factor not only focal length!
One question, if I put a 6×7 75mm lens on a 35mm “full frame” dslr (like on a Pentax K-1), what would the accurate field of view be? Would it give a wider fov or narrower fov?
It will be the same as if you put a 75mm Pentax K mount lens on your camera, but you’ll be using only a portion of the image circle.
This answer does not make sense. You said above that a 50mm full frame lens on a APS-C camera is like an 80mm field of view due to the 1.6 crop factor. So a 75mm 645 lens on a 35mm full frame camera would be like 120mm lens equivalent field of view with the crop factor.
No .. Robert is correct. Focal length is focal length .. so (provided it fits) ANY 75mm lens will give exactly the same FOV on a given aperture plate (i.e. film/sensor area) as any other 75mm lens. What you are confusing is the change in FOV between the 6by7 medium format camera and full frame camera for the same focal length.
A 75mm 645 medium format camera lens on a full frame camera (if you can fit it) has the same FOV as a 120mm lens ON a medium format camera, but the SAME FOV as any other 75 mm lens on the full frame camera. Put the 75mm lens back on the 645 camera, and the FOV is now the same as that given by a ~40mm lens on the full frame camera.
What you have to watch out for is if ever you put a lens designed for a smaller aperture plate (like a DX or APS-C sensor) on a camera with a bigger aperture plate. For example, if you put a 75mm DX lens on a full frame camera the FOV will be exactly the same as a 75mm 645 medium format lens on the full frame camera, BUT the image circle may not be large enough to cover the sensor (or film), and you may get vignetting (dark corners).
This is only a problem when there is a common mount shared between cameras with different aperture plates, like Nikon’s F mount, for example when using Nikon DX lenses on Nikon FX/35mm cameras. As far as I am aware, no medium format cameras share a common mount with a full frame/35mm camera.. so you should never have that issue when using a medium format camera.
how do you calculate the equivalents? Popular 645 format lenses and their 35mm equivalents
Williams Khürt Louis says
Wait. Wait. Wait. Since medium film (1901) format predates 35mm film (1934), the 35mm is the CROP SENSOR when we use the medium format as the reference.
This whole crop factor conversation becomes stupid since a medium format sensor is NOT CROPPING anything.
If the “crop factor” is under 1, like in all of these examples, then mathematically speaking those numbers say exactly what you are saying: multiply your focal distance by zero point something and you’ll get a wider FOV at the same lenght.
Nobody’s using medium format as a reference in this article. Actually, they are using 35mm as a reference, so anyone can understand it. It is supposed to help those migrating or starting to shoot medium format while coming from 35mm. That’s why 35mm is used as the reference: they are used to 35mm FOV and as long as the maths are accurate you can use whatever you want as your reference point.
Bottom line being: don’t be an idiot, it isn’t relevant as far as this article goes. And there is no sensor that ACTUALLY crops anything. If you use an APS designed lens on an APS sensor, the maths will still be correct and the cropping will be non-existent. Take a Nikkor 35mm AF-S DX for example… The FOV will be equivalent to a 47.5mm lens on 35mm, and yet the 35mm lens won’t work as such on that format because it’s not designed for it. Damn, I wish you people learn to understand the context before saying completely irrelevant and inaccurate things. Kudos to your wikiresearch, but you’re not helping anyone.
52.5mm* equivalent, sorry. I was more concerned about the actual subject I was writting about than the maths.
When you use 80 mm CZJ for example, what focal length it would be on 35mm camera? how to calculate that?
I have tested this extensively over the last week or so, There are more technical explanations as to the phenomenon however to keep things relatively simple here is the explanation i have come up with (sorry if it a bit rambling but trying to cover all possible questions to the points that could be raised)
FOV – effective Field Of View (observable area a person can see through his or her eyes or via an optical device, allows for coverage of an area rather than a single focused point)
DOF – Depth Of Field (the distance between the nearest and the furthest objects giving a focused image deemed to be acceptably sharp)
COC – circle of confusion (optical spot caused by a cone of light rays from a lens not coming to a perfect focus when imaging a point source)
MF – Medium Format
MFT – Micro Four Thirds (sensor)
When using the same lens on multiple sized format cameras only the FOV and effective light gathering capacity change when other aspects are constant, distance from subject and constant light levels.
150mm f4 MF designed lens mounted on a 35mm camera will give the same FOV, DOF and Light gathering capacity as a 150mm f4 35mm designed lens mounted on a 35mm camera. Using the one lens stated on a 35mm/APS-C/MFT/1″ sensor camera will produce identical DOF with the camera the same distance to the subject however the FOV will change and the effective light gathered will de different.
When that lens is mounted on a MF camera for instance a 645 MF camera you will get the same FOV as a 90mm lens on a 35mm camera however that does not make the 150mm lens a 90mm lens nor does the DOF change at the same focal distance.
For another example a 50mm f1.2 lens on MFT camera will have an effective FOV of 100mm lens compared to 35mm but also an effective light gathering capacity of 2 stops less, making the light gathering capacity of the sensor/film equivalent to F2 when compared to 35mm. Conversely an F4 lens on a 645 MF camera when compared to 35mm will collect 1.5x more light making the effective light collecting capacity of approx f2.4.
If however the focal distance is reduced by moving closer to the subject to achieve the same FOV when using a MF camera compared to a 35mm camera, due to the camera being closer to the subject, the DOF will appear shallower but that is only a function of the camera being closer to the subject.
The benefit of mounting a larger format lens on a smaller sensor is you should obtain better sharpness across the frame as you are using an area in the centre of the lens, which will appear sharper and have less vignette (fall of of light) due to physics that the outlying periphery of the projected image is substandard
Before people jump in and start talking about COC, T stop and more technical aspects of lens design and image creation including magnification factors for printing etc, to me that was not the aim of this discussion however it is no less valid as the effects of this are certainly relevant.
My apologies for the long explanation but many people seem to be touting misnomers on effective light gathering capacities (referring it to F stop), effective focal lengths (FOV not magnification/crop factor), DOF etc.
To clear up confusion my opinion manufacturers should use the following definitions:
T- Stop – To describe the effective light gathering capacity of a lens regarding to a certain sized sensor (film format)(not just for video)
F-stop – To describe the DOF a lens is able to produce.
FOV – to explain focal length for different formats not crop factor.
I hope you enjoyed reading and it helps to clear up some confusion. If however i have made any glaring mistakes please feel free to highlight them.
It’s just really equivalent field of view using 35mm as a reference. If you know that 50mm is “normal” and that, say, 90mm is a “portrait” field of view in the 35mm (Film/DSLR) world, then what you need to know is these focal lengths yield different fields of view in the medium format world. A 90mm lens becomes a “normal” lens and you need to step up to something like 190mm or 200mm in the medium format world to get a “portrait” view. Of course, the author has gone to great lengths to explain that while 35mm film cameras and DSLR’s produce a 6×9 image that is not the case in the medium format world where formats vary, such as cameras that take square pictures (i.e. 5×5). In that case, there is more work to be done to figure out what the 35mm equivalent would be after you cropped the 35mm image. Thank you for such an insightful article!