Mamiya-Sekor SF C 150mm F/4

Short telephoto prime lens • Pro • Film era • Discontinued


SF The lens features soft focus effect control.
C The multi-layer coating is applied to the surface of lens elements. It boosts light transmission, ensures sharp and high contrast images, minimizes ghosting and flares.

Production details

Announced:<No data>
Production type:Mass production
Production status: Discontinued
Original name:MAMIYA-SEKOR SF C 1:4 f=150mm
System:Mamiya RB67 (1970)

Features highlight



Optical design
Focal length:150mm
Maximum format:Medium format 6x7
Mount and Flange focal distance:Mamiya RB67 [111mm]
Diagonal angle of view:33.4° (Medium format)
Lens construction:5 elements - 3 groups
Diaphragm mechanism
Diaphragm type:Automatic
Aperture control:Aperture ring (Manual settings only)
Number of blades:<No data>
Built-in leaf shutter
Type:Mechanical Seiko #1
Speeds:1 - 1/400 + T
Closest focusing distance:0.856m
Closest working distance:0.615m
Maximum magnification ratio:1:3.33 at the closest focusing distance
Focusing modes:Manual focus only
Manual focus control:None; focusing from the camera
Physical characteristics
Maximum diameter x Length:⌀94×84mm
Filters:Screw-type 77mm
Lens hood:Screw-type (round)
Teleconverters:Not available

*) Sources of data: Manufacturer's technical data ● Interchangeable lenses for Mamiya RB67 instructions ● Mamiya interchangeable lenses for Mamiya RB67 Professional instructions ● The photograph. Mamiya RB67 Pro S booklet ● Mamiya RB67 Pro-S booklet ● Mamiya RB67 Pro-SD system accessories chart ● Mamiya RB67 Pro-SD booklet (PUB. 2112) ● Mamiya medium format cameras booklet ● Mamiya medium format cameras booklet (PUB. 9012) ● Mamiya medium format cameras booklet (PUB. 9022).

Manufacturer description #1

The variable diffusion 150mm f/4 lens is an open diaphragm soft focus lens that deliberately produces a beautiful flare. Several interchangeable diaphragms are available, including a honeycomb diaphragm, and it is possible to vary the flare by adjusting the aperture. It is ideal for portraits that are intended to convey a particular mood and for general special effects photography. Since it corresponds to the 35mm format 75mm lens, its picture angle permits it to be used even in small studios.

Manufacturer description #2

Mamiya’s long experience and concentrated technology have made possible the development of the all new Mamiya-Sekor SF C 150mm f/4 Soft Focus Lens. A special type of spherical aberration has been purposely introduced into this lens to produce photographic images that are sharp yet which have an alluring softness. And the highly advanced design using 3 new types of optical glass has made possible extremely precise correction of all other types of aberrations as in standard lenses as well as superb color balance.

The soft focus effect is eliminated when this lens is stopped down to f/8 or more so the same sharp images obtained with standard lenses are available when desired. And the soft focus effect can be varied at will by using the three different Softness Control Discs provided with the lens.

There are three different types of Softness Control Discs, each with a different diameter hole in the center. Always set this lens at full aperture (f/4) when using one of the Softness Control Discs. The f-value of this lens changes according to the Disc used. When the No. 1 Disc is used the effective lens aperture is approximately f/5; for the No. 2 Disc this value is approximately f/5.6; and for the No. 3 Disc it is approximately f/6.3.

The special spherical aberration used in this lens to produce the soft focus effect causes some discrepancy in focusing when this is done at full aperture; therefore, when focusing always stop this lens down to at least f/8 to cancel the soft focus effect.

Manufacturer description #3

The 150mm f/4.0 is a unique, special application lens offering variable soft focus and use as a normal application telephoto at smaller apertures. It is the prime lens for many portrait and wedding photographers because of its unusual and controllable soft focus effects using designed-in spherical abberation at apertures from f/4 to f/8 and a set of three diffusion discs. The combination creates soft focus images that appear sharp at the same time, eliminating the need for costly and time consuming retouching. At f/8 and smaller apertures, it renders completely sharp, normal images. Its 150mm focal length makes it ideal for small studio working distances. Applications include portraiture, fashion, beauty, landscape and general photography.

Typical application


Slow 6x7 medium-format short telephoto prime lens • Professional model (Top class)Soft Focus lens

Professional model (Top class)

  • Designed for medium format cameras

Soft Focus lens

Spherical aberration has been purposely introduced into this lens to produce photographic images that are sharp yet which have an alluring softness.

Because of the ethereal glow that can be achieved by using Soft Focus, the lens is ideal for creating scenes with a dreamy feel. It is also good for masking blemishes in portrait photography, leaving the model's skin looking flawless.

The effect of Soft Focus is a complex phenomenon that depends on focusing distance, distance to background, relative aperture etc. It is not the same as an out-of-focus image, and cannot be achieved simply by defocusing a common lens.

The effect can be approximated in post-processing but it is not as trivial as just applying a blur filter over the image.

Genres or subjects of photography (1):


Recommended slowest shutter speed when shooting static subjects handheld:

1/160th of a second

Alternatives in the Mamiya RB67 system

///// Sorted by focal length and speed, in ascending order /////

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35mm full frame

43.27 24 36
  • Dimensions: 36 × 24mm
  • Aspect ratio: 3:2
  • Diagonal: 43.27mm
  • Area: 864mm2


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Image stabilizer

A technology used for reducing or even eliminating the effects of camera shake. Gyro sensors inside the lens detect camera shake and pass the data to a microcomputer. Then an image stabilization group of elements controlled by the microcomputer moves inside the lens and compensates camera shake in order to keep the image static on the imaging sensor or film.

The technology allows to increase the shutter speed by several stops and shoot handheld in such lighting conditions and at such focal lengths where without image stabilizer you have to use tripod, decrease the shutter speed and/or increase the ISO setting which can lead to blurry and noisy images.

Original name

Lens name as indicated on the lens barrel (usually on the front ring). With lenses from film era, may vary slightly from batch to batch.


Format refers to the shape and size of film or image sensor.

35mm is the common name of the 36x24mm film format or image sensor format. It has an aspect ratio of 3:2, and a diagonal measurement of approximately 43mm. The name originates with the total width of the 135 film which was the primary medium of the format prior to the invention of the full frame digital SLR. Historically the 35mm format was sometimes called small format to distinguish it from the medium and large formats.

APS-C is an image sensor format approximately equivalent in size to the film negatives of 25.1x16.7mm with an aspect ratio of 3:2.

Medium format is a film format or image sensor format larger than 36x24mm (35mm) but smaller than 4x5in (large format).

Angle of view

Angle of view describes the angular extent of a given scene that is imaged by a camera. It is used interchangeably with the more general term field of view.

As the focal length changes, the angle of view also changes. The shorter the focal length (eg 18mm), the wider the angle of view. Conversely, the longer the focal length (eg 55mm), the smaller the angle of view.

A camera's angle of view depends not only on the lens, but also on the sensor. Imaging sensors are sometimes smaller than 35mm film frame, and this causes the lens to have a narrower angle of view than with 35mm film, by a certain factor for each sensor (called the crop factor).

This website does not use the angles of view provided by lens manufacturers, but calculates them automatically by the following formula: 114.6 * arctan (21.622 / CF * FL),


CF – crop-factor of a sensor,
FL – focal length of a lens.


A lens mount is an interface — mechanical and often also electrical — between a camera body and a lens.

A lens mount may be a screw-threaded type, a bayonet-type, or a breech-lock type. Modern camera lens mounts are of the bayonet type, because the bayonet mechanism precisely aligns mechanical and electrical features between lens and body, unlike screw-threaded mounts.

Lens mounts of competing manufacturers (Canon, Nikon, Pentax, Sony etc.) are always incompatible. In addition to the mechanical and electrical interface variations, the flange focal distance can also be different.

The flange focal distance (FFD) is the distance from the mechanical rear end surface of the lens mount to the focal plane.

Lens construction

Lens construction – a specific arrangement of elements and groups that make up the optical design, including type and size of elements, type of used materials etc.

Element - an individual piece of glass which makes up one component of a photographic lens. Photographic lenses are nearly always built up of multiple such elements.

Group – a cemented together pieces of glass which form a single unit or an individual piece of glass. The advantage is that there is no glass-air surfaces between cemented together pieces of glass, which reduces reflections.

Focal length

The focal length is the factor that determines the size of the image reproduced on the focal plane, picture angle which covers the area of the subject to be photographed, depth of field, etc.


The largest opening or stop at which a lens can be used is referred to as the speed of the lens. The larger the maximum aperture is, the faster the lens is considered to be. Lenses that offer a large maximum aperture are commonly referred to as fast lenses, and lenses with smaller maximum aperture are regarded as slow.

In low-light situations, having a wider maximum aperture means that you can shoot at a faster shutter speed or work at a lower ISO, or both.

Closest focusing distance

The minimum distance from the focal plane (film or sensor) to the subject where the lens is still able to focus.

Closest working distance

The distance from the front edge of the lens to the subject at the maximum magnification.

Magnification ratio

Determines how large the subject will appear in the final image. For example, a magnification ratio of 1:1 means that the image of the subject formed on the film or sensor will be the same size as the subject in real life. For this reason, a 1:1 ratio is often called "life-size".

Manual diaphragm

The diaphragm must be stopped down manually by rotating the detent aperture ring.

Preset diaphragm

The lens has two rings, one is for pre-setting, while the other is for normal diaphragm adjustment. The first ring must be set at the desired aperture, the second ring then should be fully opened for focusing, and turned back for stop down to the pre-set value.

Semi-automatic diaphragm

The lens features spring mechanism in the diaphragm, triggered by the shutter release, which stops down the diaphragm to the pre-set value. The spring needs to be reset manually after each exposure to re-open diaphragm to its maximum value.

Automatic diaphragm

The camera automatically closes the diaphragm down during the shutter operation. On completion of the exposure, the diaphragm re-opens to its maximum value.

Fixed diaphragm

The aperture setting is fixed at F/4 on this lens, and cannot be adjusted.

Number of blades

As a general rule, the more blades that are used to create the aperture opening in the lens, the rounder the out-of-focus highlights will be.

Some lenses are designed with curved diaphragm blades, so the roundness of the aperture comes not from the number of blades, but from their shape. However, the fewer blades the diaphragm has, the more difficult it is to form a circle, regardless of rounded edges.

At maximum aperture, the opening will be circular regardless of the number of blades.


Excluding case or pouch, caps and other detachable accessories (lens hood, close-up adapter, tripod adapter etc.).

Maximum diameter x Length

Excluding case or pouch, caps and other detachable accessories (lens hood, close-up adapter, tripod adapter etc.).

For lenses with collapsible design, the length is indicated for the working (retracted) state.

Weather sealing

A rubber material which is inserted in between each externally exposed part (manual focus and zoom rings, buttons, switch panels etc.) to ensure it is properly sealed against dust and moisture.

Lenses that accept front mounted filters typically do not have gaskets behind the filter mount. It is recommended to use a filter for complete weather resistance when desired.

Fluorine coating

Helps keep lenses clean by reducing the possibility of dust and dirt adhering to the lens and by facilitating cleaning should the need arise. Applied to the outer surface of the front and/or rear lens elements over multi-coatings.


Lens filters are accessories that can protect lenses from dirt and damage, enhance colors, minimize glare and reflections, and add creative effects to images.

Lens hood

A lens hood or lens shade is a device used on the end of a lens to block the sun or other light source in order to prevent glare and lens flare. Flare occurs when stray light strikes the front element of a lens and then bounces around within the lens. This stray light often comes from very bright light sources, such as the sun, bright studio lights, or a bright white background.

The geometry of the lens hood can vary from a plain cylindrical or conical section to a more complex shape, sometimes called a petal, tulip, or flower hood. This allows the lens hood to block stray light with the higher portions of the lens hood, while allowing more light into the corners of the image through the lowered portions of the hood.

Lens hoods are more prominent in long focus lenses because they have a smaller viewing angle than that of wide-angle lenses. For wide angle lenses, the length of the hood cannot be as long as those for telephoto lenses, as a longer hood would enter the wider field of view of the lens.

Lens hoods are often designed to fit onto the matching lens facing either forward, for normal use, or backwards, so that the hood may be stored with the lens without occupying much additional space. In addition, lens hoods can offer some degree of physical protection for the lens due to the hood extending farther than the lens itself.


Teleconverters increase the effective focal length of lenses. They also usually maintain the closest focusing distance of lenses, thus increasing the magnification significantly. A lens combined with a teleconverter is normally smaller, lighter and cheaper than a "direct" telephoto lens of the same focal length and speed.

Teleconverters are a convenient way of enhancing telephoto capability, but it comes at a cost − reduced maximum aperture. Also, since teleconverters magnify every detail in the image, they logically also magnify residual aberrations of the lens.

Lens caps

Scratched lens surfaces can spoil the definition and contrast of even the finest lenses. Lens covers are the best and most inexpensive protection available against dust, moisture and abrasion. Safeguard lens elements - both front and rear - whenever the lens is not in use.