Pentax Rear Converter-A 2X-S

Teleconverter • Film era • Discontinued



Production details:
Production status: Discontinued
System: Pentax K (1975)
Optical design:
Magnification factor:2x
Maximum format:35mm full frame
Mount:Pentax K
Lens construction:7 elements - 6 groups
Physical characteristics:
Maximum diameter x Length:⌀64.5×39mm
Weather sealing:-
Super Protect (SP) coating:-
Sources of data:
1. Manufacturer's technical data.
2. Pentax 35mm SLR lenses (September 1989).
3. Pentax 35mm SLR lenses.

Manufacturer description #1

Pentax Rear Converters allow 1.4X (w/1.4X-S or -L) or 2X (w/2X-S or -L) increase of the focal length and f-number of the lens in use when this converter is mounted between the lens and camera body. These converters have lens information contacts, which enable all AE programs on Pentax KA- or KAF- mount camera to operate with Pentax compatible lens. When combined with Pentax K-mount camera and compatible lenses, open aperture metering and automatic aperture are coupled.


If the Rear Converter is mounted between the KAF-mount camera and F lens, the auto focus does not function.

Manufacturer description #2

Fitting between the lens and the camera body, these rear converters increase effective focal length of the lens. 1.4X models boost focal length 40%, nearly doubling image area; 2X models double focal length. Models S are usable with most lenses up to 300mm while models L are for lenses over 300mm. All four can be used with automatic aperture control and open-aperture metering.

Manufacturer description #3

The rear converters can extend the effective focal length of a lens. The 1.4X models increase the focal length by 40% and nearly double the image size while the 2X models can double the focal length. The S models fit most Pentax lenses while the L models are specially designed for use with telephoto and super-telephoto lenses for an even stronger telephoto effect. They also maintain automatic diaphragm control and open-aperture exposure metering.

Manufacturer description #4

Positioned between a camera body and a taking lens, these rear converters increase the effective focal length of the lens. The two 1.4X models boost the focal length by 40% and nearly double the image area while the two 2X models double the focal length. The S models fit most SMC Pentax lenses while the L models are specifically designed for telephoto and super-telephoto lenses to bring out their optimum performance. All rear converters can be used with automatic diaphragm control and open-aperture light metering.

Compatible lenses (91)

smc Pentax-A 16mm F/2.8 Fish-eye 1984 
smc Pentax-F 17-28mm F/3.5-4.5 Fish-eyePro 1995 
smc Pentax-A 20mm F/2.8 ⌀67Pro 1985 
smc Pentax-FA 20mm F/2.8 ⌀67Pro 1995 
smc Pentax-FA 20-35mm F/4 AL ⌀58 1998 
smc Pentax-A 24mm F/2.8 ⌀52 1983 
smc Pentax-FA* 24mm F/2 AL [IF] ⌀67 1991 
smc Pentax-A 24-50mm F/4 ⌀58 1983 
smc Pentax-F 24-50mm F/4 ⌀58 1987 
smc Pentax-FA 24-90mm F/3.5-4.5 AL [IF] ⌀67 2001 
smc Pentax Shift 28mm F/3.5Pro 1975 
smc Pentax-A 28mm F/2.8 ⌀49 1983 
smc Pentax-F 28mm F/2.8 ⌀49 1987 
smc Pentax-FA 28mm F/2.8 AL ⌀49 1991 
smc Pentax-FA 28mm F/2.8 Soft ⌀49 1997 
smc Pentax-A 28mm F/2 ⌀49 1983 
smc Pentax-FA 28-70mm F/4 AL ⌀52Pro 1995 
smc Pentax-FA* 28-70mm F/2.8 PZ AL ⌀67Pro 1993 
smc Pentax-FA 28-80mm F/3.5-5.6 ⌀58 1998 
smc Pentax-FA J 28-80mm F/3.5-5.6 AL ⌀58 2003 
smc Pentax-F 28-80mm F/3.5-4.5 ⌀58 1987 
smc Pentax-FA 28-105mm F/4-5.6 PZ ⌀58 1991 
smc Pentax-FA 28-105mm F/4-5.6 [IF] ⌀62 1999 
smc Pentax-FA 28-105mm F/3.2-4.5 AL [IF] ⌀62 2001 
smc Pentax-A 28-135mm F/4 ⌀77 1983 
smc Pentax-FA 28-200mm F/3.8-5.6 AL [IF] ⌀72 1998 
smc Pentax-FA 31mm F/1.8 AL Limited ⌀58 2001 
smc Pentax-A 35mm F/2.8 ⌀49 1983 
smc Pentax-A 35mm F/2 ⌀49 1983 
smc Pentax-FA 35mm F/2 AL (Schneider-Kreuznach D-Xenogon) ⌀49 1999 
smc Pentax-F 35-70mm F/3.5-4.5 ⌀49 1987 
smc Pentax-FA 35-80mm F/4-5.6 ⌀49 1999 
smc Pentax-F 35-105mm F/4-5.6 ⌀58 1988 
smc Pentax-A 35-135mm F/3.5-4.5 ⌀58Push/pull 1986 
smc Pentax-F 35-135mm F/3.5-4.5 ⌀58 1987 
smc Pentax-FA 43mm F/1.9 Limited ⌀49Pancake lens 1997 
smc Pentax-F 50mm F/2.8 Macro ⌀521:1 @ 0.195m 1988 
smc Pentax-FA 50mm F/2.8 Macro ⌀521:1 @ 0.195m 1991 
smc Pentax-A 50mm F/2 ⌀49 1985 
smc Pentax-A 50mm F/1.7 ⌀49 1983 
smc Pentax-F 50mm F/1.7 ⌀49 1987 
smc Pentax-FA 50mm F/1.7 ⌀49 1991 
smc Pentax-F 50mm F/1.4 ⌀49Pro 1987 
smc Pentax-FA 50mm F/1.4 ⌀49Pro 1991 
HD Pentax-FA 50mm F/1.4 ⌀49Pro 2023 
smc Pentax-FA 50mm F/1.4 Classic ⌀49Pro 2023 
smc Pentax-A 50mm F/1.2 ⌀52 1983 
smc Pentax-FA 70-200mm F/4-5.6 PZ ⌀49 1991 
smc Pentax-F 70-210mm F/4-5.6 ⌀49 1987 
smc Pentax-FA J 75-300mm F/4.5-5.8 AL ⌀58 2003 
smc Pentax-FA 77mm F/1.8 Limited ⌀49 1999 
smc Pentax-F 80-200mm F/4.7-5.6 ⌀49 1993 
smc Pentax-FA 80-200mm F/4.7-5.6 ⌀49 1999 
smc Pentax-FA* 80-200mm F/2.8 ED [IF] PZ ⌀77Pro 1994 
smc Pentax-FA 80-320mm F/4.5-5.6 ⌀58 1997 
smc Pentax-FA 85mm F/2.8 Soft ⌀52 1995 
smc Pentax 85mm F/2.2 Soft ⌀49 1985 
smc Pentax-A* 85mm F/1.4 ⌀67 1984 
smc Pentax-FA* 85mm F/1.4 [IF] ⌀67Pro 1992 
smc Pentax Bellows 100mm F/4 ⌀52For bellowsPro 1975 
smc Pentax-FA 100mm F/3.5 Macro ⌀491:2 @ 0.43mPro 1998 
smc Pentax-A 100mm F/2.8 ⌀49 1984 
smc Pentax-F 100mm F/2.8 Macro ⌀581:1 @ 0.306mPro 1987 
smc Pentax-FA 100mm F/2.8 Macro ⌀581:1 @ 0.306mPro 1991 
smc Pentax-FA 100-300mm F/4.7-5.8 ⌀58 2000 
smc Pentax-F 100-300mm F/4.5-5.6 ⌀58 1995 
smc Pentax-A 135mm F/2.8 ⌀52 1983 
smc Pentax-F 135mm F/2.8 [IF] ⌀52 1987 
smc Pentax-FA 135mm F/2.8 [IF] ⌀52 1991 
smc Pentax-A* 135mm F/1.8 ⌀77 1984 
smc Pentax 135-600mm F/6.7Push/pull 1975 
smc Pentax-A 200mm F/4 ⌀52 1983 
smc Pentax-A* 200mm F/4 ED Macro ⌀581:1 @ 0.55mPro 1986 
smc Pentax-FA* 200mm F/4 ED [IF] Macro ⌀671:1 @ 0.5mPro 2000 
smc Pentax-A* 200mm F/2.8 ED ⌀77 1982 
smc Pentax-FA* 200mm F/2.8 ED [IF] ⌀77Pro 1992 
smc Pentax-F* 250-600mm F/5.6 ED [IF] ⌀112Pro 1988 
smc Pentax-FA* 250-600mm F/5.6 ED [IF] PZ ⌀112Pro 1991 
smc Pentax-F* 300mm F/4.5 ED [IF] ⌀67Pro 1987 
smc Pentax-FA* 300mm F/4.5 ED [IF]Pro 1991 
smc Pentax-A* 300mm F/2.8 ED [IF]Pro 1983 
smc Pentax-FA* 300mm F/2.8 ED [IF] ⌀112Pro 1993 
smc Pentax-A 400mm F/5.6 ⌀77Pro 1984 
smc Pentax-FA* 400mm F/5.6 ED [IF] ⌀77Pro 1997 
smc Pentax-A* 400mm F/2.8 ED [IF]Pro 1984 
smc Pentax Reflex 400-600mm F/8-12 ⌀67 1982 
smc Pentax 500mm F/4.5Pro 1975 
smc Pentax-F* 600mm F/4 ED [IF] ⌀150Pro 1988 
smc Pentax Reflex 1000mm F/11 1977 
smc Pentax 1000mm F/8Pro 1975 
smc Pentax-M Reflex 2000mm F/13.5 1982 
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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 focus override in autofocus mode

Allows to perform final focusing manually after the camera has locked the focus automatically. Note that you don't have to switch camera and/or lens to manual focus mode.

Manual focus override in autofocus mode

Allows to perform final focusing manually after the camera has locked the focus automatically. Note that you don't have to switch camera and/or lens to manual focus mode.

Electronic manual focus override is performed in the following way: half-press the shutter button, wait until the camera has finished the autofocusing and then focus manually without releasing the shutter button using the focusing ring.

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/ 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.