Lens Rehousing  -  Mamiya 645 inc. Speed Booster

Lens Rehousing  -  Mamiya 645 inc. Speed Booster

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Mamiya 645 Lenses

Rehousing Mamiya 645 Lenses

The Mamiya 645 rehousing project is a unique venture for TLS so far. It was decided to offer the Mamiya 645 Sekor C lenses as both a standard rehousing, but also with the option of a built-in speed booster. Both versions of the rehousing have 95mm fronts as standard. The original lenses were designed to cover a film area of 6cm x 4.5cm, this means that the lenses all cover the Alexa 65 sensor as standard. However, rehousing them with the built-in speed booster still allows the lenses to cover all full frame sensors, including LF open gate, while improving the speed of the base lens by one stop. The Mamiya 645 Sekor C lenses were developed during the 1970s and released during the second half of the decade. The lenses boasted a multi-layer coating and sharp, clean optics from corner to corner. They produce smooth out of focus areas and are well matched across the focal lengths. These lenses provide a bridge between the classic ‘vintage’ look and modern optical designs and coatings that manufacturers produce to date.

Speed boosting a Mamiya 645

The speed booster is essentially a 0.71x adaptor that sits at the rear of the original base lens. Therefore, it works by concentrating the light transmitted through the lens, onto a smaller surface area than it was originally designed for. This has two major benefits for the Mamiya 645 lenses. Firstly, it increases the speed of the lens by one f-stop. An original lens with an aperture of f2.8 becomes a rehoused lens with a T stop of T2.3/f2 (remember that f-stop is a formulated amount of light whereas T-stop is actual light transmitted through the lens). Not only this, but it reduces the focal length of the lens as well. Therefore, a 35mm base lens becomes a 25mm once rehoused with the speed booster.

The beauty of this combination is the effect it has on the optical performance of the lens. Introducing the speed booster to these lenses adds a soft fall off towards the edges of the frame. Therefore, the speed boosted lens renders a beautiful cinematic characteristic not seen in the original lens. As the speed booster is built into the rehousing, it is unnoticeable from an aesthetic point of view too. Although most popular in LPL mount, TLS are also able to offer a PL mount for this option too.

Designed for the future

There is also a hidden beauty with the design of the Mamiya 645 rehousing too. Once the lenses have been rehoused to incorporate the speed booster, it is removable. With some basic tools and little knowledge, the end user can remove the speed booster from the rehousing. This then allows the lens to cover for even larger sensors that may be produced in the future. To keep the markings on the outside of the lens correct, TLS can supply new covers with the amended focal length and T-stop as well as an iris gear marked up without the speed booster attached. These parts are easily interchanged, though TLS would need the lens to mark up the new iris scale unless it was ordered at the same time as the rehousing process.

Mamiya 645 Lenses Specification

17mm 19mm 25mm 32mm 39mm 50mm 57mm 57mm 78mm 107mm 107mm
T-Stop 3.3 T2-T22 2.8 2.3 2.3 2.3 2.3 1.6 2.3 2.2 2.6
Min. Object Distance typ. 11" 11" 12" 14" 16" 21" 2'1 2'1 3'7 3'9 3'9
Front Diameter (mm) 134mm 143mm 95mm 95mm 95mm 95mm 95mm 95mm 95mm 95mm 95mm
Total Length *(mm) 104 155mm 93.7 108.7 (C)
103.7 (CN)
93.7 (S/N)
108.7 (C)
93.7 93.7 93.7 93.7 151.1 118.7
Total Length *(inches) 4.1 2.6 3.7 4.3 (C)
4.1 (CN)
3.7 (S/N)
4.3 (C)
3.7 3.7 3.7 3.7 5.9 4.7

* Total approximate length is measured from the flange to the front of lens


These stills were taken when filming a commercial for Pilot Travel Centers, in Albuquerque, New Mexico. The commercial was shot on a Sony Venice in 6K Raw with the Mamiya 645 speed boosted lenses.

Images were kindly provided by Nathan Thompson DOP.

'To inspire through innovation, passion and quality'
'To inspire through innovation, passion and quality'