Medium Format Focal Reducer

Full frame cinematography is pretty new; although we had a few Large Format exceptions with 75mm cinematography and the Alexa 65 (54.12 mm x 25.58 mm), S-35mm has been the dominating factor in cinematography now for many years. We don’t want this to become another in depth articel about image formats. so If you’re new to this game please have a nice read here about Full Frame cinematography and 65.

In this article we want to show our love for Mamiya 645 lenses and why we love them more than our own child. To get a better understanding of why and how we use a ‘Speedbooster’ to adapt them to to the Mavo LF (or Mavo edge), we’ve made a few image circle graphic representations.

Medium Format and Full Frame comparison
Medium Format and Full Frame comparison

Projection circles

As we can see a Medium Format (from now on MF) lens like a Mamiya Sekor C throws out a much larger projection circle than a Full Frame (from now on FF) lens. Please note that a real image (projection) circle looks a hell lot differently as on this simple representation.

Lens projection circle
Lens projection circle

Like on every lens system, a longer focal length tend to output a larger image circle than a wide focal length. Wide angle lenses tend to have more vignetting, edge sharpness fall off and barrel distortion, especially when it goes for vintage lenses. Most probably because we want them to be wide, and its pretty hard to design a good wide angle, so most of the image circle is used for projecting onto the sensor/film. For longer focal lengths we have a bit more luxury to overthrow them and only use the best part of the circle. Nowadays with computer designed lenses like Lowa zero-d lenses a lot more is possible than it was before. Gafpa Gear is by no means a sucker for wide angle glass. Yes the work from Lubezki in cooperation with Malick and later Alejandro Inarritu was interesting. even one of the members of Gafpa Gear had the honors to work with both, but now 9 years after the release of Tree of Life we have to conclude that extreme-wide-angle-cinematography is in Gafpa’s eyes a false attempt and doesn’t resolve the challenges cinematography is facing. But this is subjective of course. If we look at Mamiyas offerings in their 645 line up, the widest non-fisheye lens they have is a 35mm. when hooked on a medium format lens, this lens will have AOV which equals a 24mm on full frame or 16mm on s-35mm (aps-c). I would say its not a crazy wide angle, more like standard wide angle. But when deployed on a full frame sensor without ‘speedbooster’/’focal reducer’ it will remain a 35mm but won’t reveal the full width its capable of displaying, because the image circle overthrows about a factor of 1.5X.

Image circles overlapping
Image circles overlapping

Crop Factors

Even though we haven’t talked about why you would want to shoot Medium Format, we’ve learned one thing so far. MF lenses output a much bigger image circle than FF lenses. To see the full image a MF lens is able to resolve we have to either put it on a MF camera, or compress the image circle with the help of a high grade focal reducer (speedbooster) onto a FF camera. A FF sensor/film is about 1.5 times smaller than the 645 MF dimension. That brings us to ‘Crop Factors’. Since we standardize the FF format in cinematography as the biggest format which exists we say that FF has a crop factor of 1.0 and s35mm (APS-C) has a crop factor of 1.5X over FF.

So if we want to expres the crop factor of a MF like the 645 format and we know that its around 1.5X bigger than FF we have to make the following calculation to express the crop factor in relation to FF as a standard: 1/1.5= 0.67X

So in order to calculate a equivalent angle of view we have to multiply a MF focal length by 0.67X in order to find its FF equivalent.

So a 70mm MF lens on a MF camera will have the same AOV (angle of view) as a 47mm lens on a FF camera (70*0.67=46.9). Or a 70mm lens on a FF camera has a equivalent AOV as a 105mm MF lens on a MF camera (70:0.67=104.48)

Speedbooster/Focal Reducer

For those who have used a film spot light with for instance a focusable fresnel lens or a parabolic reflector it’s easy to understand what a ‘Speedbooster’ does. If you compress the beam of light onto a smaller circle the lux per square mm will be higher than if you would decompress the beam of light and project a bigger circle. The total amount of light is the same but the amount of light per square mm is different and thats what matters when you’re working with either film cameras or digital cameras. So by taking the much larger image circle of a MF lens and compress it and output it as a FF image circle you gain light, so your lens basically becomes in this case a stop of light more brighter. If we would mount a T2.0 lens like a Mamiya sekor 80mm f1.8 to a Kipon focal reducer, it will output a T1.4. Please note that this is a bit of a odd way of describing this because f-stop affects DOF but a speedbooster only affects brightness. We would say that the ‘speedboost’ which is referring to the gain in brightness should be seen as a side-effect. The reason we want to apply this optical system is to see the full width of our lenses that were intended for a larger frame than the one we are shooting on. So lets go with the term ‘Focal Reducer’ .

Medium Format with a Speedbooster
Medium Format with a Speedbooster

Focal reducer

While there are many focal reducers out there, there’s currently only one focal reducer that can take a Medium Format image circle and reduce it to a Full Frame circle. It’s the Kipon Baveyes 645 to sony e-mount.t’ it has a 0.7X reducing factor which is pretty close to the previously stated 0.67X . So if we take a 70mm medium format lens on this Focal Reducer it will compress the full image circle of this lens by a factor of 0.7X which is 49mm. So a 50mm lens mounted on a full frame camera without any speedbooster will have a equivalent Angle of View as 70mm MF lens with this speedbooster mounted to the same camera.

So we virtually could say we did two things

1. we virtually enlarged the sensor size of our camera by 1.5X or

2. we virtually reduced the focal length of our MF lens.

Both statements are not completely true

  1. we only compressed the image circle so it fits the FF format, but the effect is that the lenses now behave the same as on a MF camera and as the FF camera with Focal Reducer, with the added benefit of 1 stop gain in brightness
  2. The 70mm lens remains the same 70mm lens both on MF as on FF, it behaves exactly the same in terms of DOF (depth of view) and almost the same in AOV (0.67 vs 0.7)
Kipon Speed Booster for MF 645
Kipon Speed Booster for MF 645

Now the affiliated part 🙂 Kinefinity with their modular lens mount system is the only brand -besides Sony themselves – that can have an e-Mount as a lens mount option. Even better due to the modular system changing a lens mount is as easy as changing a lens. The positive lock e-mount of Kinefinity assures a wiggle-free connection between the Kipon and the camera. To be able to do this marvelous compression on the projection circle Kipon needs quite some depth to incorporate all the lens elements, and therefor they choose for very short flange distance mounting options like the E-mount. The Kinefinity Mavo LF and Mavo edge are not only FF but the e-mount makes it a great option to turn your camera into MF. But now the most important question remains? Why do we want these Medium format lenses on our camera?

Medium Format demystified

There are quite a few misconceptions about why you would use Medium Format glass on a FF camera with a speedbooster thats capable of showing you the full width of these lenses. To start off: No we wouldn’t suggest to use a medium format lens when your looking for tiny depth of few, the highest rated medium format lens in terms of aperture is the Mamiya sekor c 80mm f1.8 and it has an inbuild fog filter, which means that if you use it below f4.0 is that it equals a 2X white diffusion filter.

DOF comparison between MF & LF
DOF comparison between MF & LF

Even though focal length is an important value in creating tiny DOF, we have to consider that a medium format lens with the kipon speedbooster is only 0.7X wider. So a 80mm MF lens with speedbooster on the Mavo lf equals a 56mm without a speedbooster. As we know there are many FF lenses out there which can go all the way up to 1.4 or even higher, so that basically evens out the differences between focal lengths in terms of DOF differences. Also most MF lenses don’t come with apertures faster than f2.8 and most are only decent stopped down to f4.0 or f5.6.

So summed up: No you don’t buy a MF lens to go crazy in terms of DOF. So why would you buy a speedbooster then?

Two reasons

1.You get the full image of the lens, so more distortion and other characteristics which we love on these lenses

2. Without the speedbooster you can’t really go wide, since the 35mm is the widest lens available in the 645 line up (yes they have a 24mm but its a fish eye). But with a speed booster this equals a 24mm which is a good wide angle for FF. so if your a sucker for wide you need this focal reducer. Also you gain one stop from the speedbooster.

Before we actually get to the point lets add one more point to the ever growing list of why you don’t want a MF lens. A lot of people often refer to the ‘Medium Format’ look, and yes back in the film days that look really existed, and now it mostly exists in the marketing heads of the Hasselblad marketing team. A bigger Film format would mean smaller grain samples, thus a cleaner image, with more resolution. And yes that was truly how it was with analogue film. But these days with modern image sensors there’s barely any difference in noise samples compared to film grain. Yes there are some amazing cameras out there like the extremely expensive Phase One cameras (some are over €60.000,-) which have 16 bit adc readout and super nice image sensors, though rolling shutter remains a big issue on these cameras. But in this case its not the image dimension which makes it state of the art but mostly sensor and readout tech (though dimension helps with the k’s in terms of MP). Its more a heritage of MF that high end company jump in that gap and make high end cameras because Medium Format is ingrained in the photography world as high end.

Phase One Medium Format camera
Phase One Medium Format camera

Mamiya Medium Format Sekor C lenses

Lets now talk about why I love those medium format lenses! For me in 2020 there’s no real advantage of using sensors with big dimension, especially now that we have great focal reducers and focal extenders, so that we can adapt to about any format with a camera.

As I just went through the process of making a Kinefinity Kinelog3 to Arri log c curve (a new blog-post is coming up covering that), I realized that two images from different sources can’t be matched fully, maybe they can if you do a custom grade for every image, but not as a preset. That’s because no camera is linear, which means that it sees every color at different luminescence in a non-linear way. Also an Arri just sees the world slightly different, this doesn’t have anything to do with inherent color matrix (color science), but more with sensor design. The same goes for lenses, its too simplistic to say, one lens has a bit more green and the other more magenta. No there have been numerous complete different optical designs over the last 150 years and no one is perfect, and also the art of cinematography is about transforming an image not to copy reality. Cinema kills theater and theater kills cinema. That said, its also too simplistic that one lens has a more vintage look, because it flares more due to the lack of coating or an older coating design, or to say that one lens has more micro sharpness or less blooming. No for me the differences in lenses are more about contrast and how it perceives and renders colors and how it distorts. The Mamiya lenses in that regard are so much different from any lens I’ve ever tried.

Batman the Dark Knight Rises

Batman the Dark Knight Rises
Batman the Dark Knight Rises
Batman the Dark Knight Rises

Normally it’s hard to see the differences between lenses after a grade, but with the Mamiyas and the way how they perceive colors its a completely different story. As an example look at the Batman film ‘The dark Knight rises’, from a narrative or conceptual artistic point of view not so interesting (to us), but from a lens look and cinematography point of view very interesting.

Batman the Dark Knight Rises
Batman the Dark Knight Rises
Batman the Dark Knight Rises
Batman the Dark Knight Rises

We would say that a lot you see there is caused by how the Mamiya render light. Also the falloff of sharpness due to the placement of the aperture, lens design and the large image circle, is super cool. Skin tones are unique, very saturated and all mapped to a very pleasing pink quality. You can extract colors from highlights and skin tones you didn’t knew your camera could perceive, while you never find yourself dialing unwanted sick colors. All the artifacts are nice including dispersion and barrel distortion and blooming. Most FF lenses have a quite steep fall of curve which means, that the difference between the point where it renders sharp -within the circle of confusion- and the point where its completely out of focus is much smaller than with these lenses. In the case of MF lenses its very hard to see the transition between sharp and blur, its super smooth! So yes they don’t have smaller depth of view, but they render depth of view completely differently.

Medium Format

This article is not about where to buy a lens and how you cine mod lenses, and how you can check your newly bought lens for fungus or haze or oil on the blades etc. But what I would like to point out is that the following lenses are my favorites in order of appearance.

  1. Mamiya sekor c 70mm leave shutter
  2. Mamiya sekor c 45 mm (the old version so not N coating and plastic build)
  3. Mamiya sekor c 110 mm (the old version with that l gold coating and strong build)
  4. Mamiya sekor c 80mm f1.8 (the 2.8 is much sharper but the 1.8 has the voodoo)
  5. Mamiya sekor c 35mm f3.5 (hard to find without haze but marvelous and sexy distortion, also use it quite a lot without a speed booster to have a little bit less pronounced distortion and a medium lens perspective)
  6. Mamiya sekor c 55mm (because it fills the gap, but not my favorite focal length)
  7. mamiya sekor c 150 mm
  8. mamiya sekor c 250mm (fun to have if you want to compress 3d space)

Please note that Mamiya also have macro versions of some lenses, I own them all but never put them to use. Instead I use diopters.

Hope this small essay helped a bit in understanding why I have advised numerous filmmakers to have a look at Mamiya glass, both for their look , affordability, build quality, and of course the easiness of cine-modding them. And because we are a share/stakeholder in Mamiya glass 🙂

One Comment

  • Geoff Bassett says:

    Wonderful article, just recently purchased the 35, 45, and 80mm 1.8 and love the look as well.
    I thought the 70mm 2.8 cannot be used adapted because of the leaf shutter mechanism?

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