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Praktica B200 electronic

aka PRAKTICA BCX electronic

35mm MF film SLR camera

Specification

Production details:
Announced:October 1978
System:● Praktica B (1978)
Format:
Maximum format:35mm full frame
Film type:135 cartridge-loaded film
Mount and Flange focal distance:Praktica B [44.4mm]
Shutter:
Type:Focal-plane
Model:Electronically controlled
Speeds:40 - 1/1000 + B
Exposure:
Exposure metering:Through-the-lens (TTL), open-aperture
Exposure modes:Aperture-priority Auto
Manual
Physical characteristics:
Weight:530g
Dimensions:138x87.5x49mm

Manufacturer description #1

The PRAKTICA B 200 is the first model of a completely new PRAKTICA range - a miniature reflex camera with fully automatic shutter-speed control but with dimensions of a real compact camera.

The PRAKTICA B 200 has an optimum of operating comfort which admits you of concentrating fully to picture composition. Without taking the camera off your eye you can focus, preselect an appropriate diaphragm numeral, release the shutter - while all the rest is done by the camera.

The technological perfection of the camera is coined by its highly integrated microelectronics packed on a modern, flexible circuit board and by its comfortable, aesthetic design. It is the scientific and technological progress by which the new PRAKTICA era is characterized and which brought us a novel type of lens mount: the PRAKTICA bayonet represents the striking feature of the PRAKTICA B 200 and of all PRAKTICA cameras to follow. The computer technology of the PRAKTICA B 200 is fascinating.

Faster than man is able to read, the camera chooses the exact shutter speed for a preselected aperture and controls the shutter infinitely within the speed range from 40 seconds to 1/1000 seconds. Light emitting diodes - LED - on the edge of the finder image give clear and unambigous information about the determined shutter speed or they signal the correct speed setting for the semi-automatic mode of operation. The possibility of switching over to semi-automatics offers a wide speed range to all these photographers who wish to set shutter speeds completely individually. Either with the convenient and quick photographing by means of the automatics or in the semi-automatic mode - the PRAKTICA B 200 is amazing by its very bright and large finder image since internal metering is at open aperture, the diaphragm values being electronically transmitted from the lens into the computer of the camera. The diaphragm numerals are reflected into the lower edge of the finder image.

The PRAKTICA B 200 is prepared to receive a motor drive.

The new PRAKTICA system

In its constructional features the PRAKTICA B 200 differs highly from the hitherto manufactured SLR cameras of the PRAKTICA family. Moreover, the new PRAKTICA system is characterized by a new and special programme of high performance lenses and accessories. The PRAKTICA B 200 is of high versatility, and its application comprises close-ups and macrophotography, micro and astrophotography as well as reproductions, optical slide copying and many other special tasks encountered in science and technology. The camera can be easily adapted to any photographic tasks so that it becomes the universally applicable device for amateurs and professionals. The use of an adapter allows also to utilize the wide programme of PRAKTICA lenses all fitted with the international M 42x1 thread connection. And the complete, already available PRAKTICA accessories for the ocular can be applied, too.

Information centre - the finder image

One glance through the large and bright viewfinder of the PRAKTICA B 200 suffices to gather all data which are necessary for exposing. Clear and without delay you are informed by 16 light emitting diodes about the triggered shutter speeds as well as the relevant boundary values, and the actual mode of operation - automatics or semi-automatics - is signalled, too. The LEDs react essentially quicker than needle instruments and distinguish themselves by their insensitivity against extreme temperatures and climatic fluctuations. The light signals are excellently visible under any light condition because in the PRAKTICA B 200 their brightness is automatically matched to the brightness of the finder image which again is influenced by the subject to be taken. As soon as the electronic speed value has been formed, the signal glows constantly at the relevant digit of the speed scale within the range from 8 sec. to 1/1000 sec. When using the semi-automatic mode, the signal flashes at the digit of the set fixed value. Flashing signals at "OVER" or "UNDER" indicate over and under exposure, resp. The arrangement of the light emitting diodes outside the finder image ensures an unaffected and reliable judgement of the subject. The diaphragm numeral which had been set is reflected into the lower edge of the finder image. Without taking the camera from your eye you are so informed about all data necessary for taking and about the mode of operation. For quick and reliable viewing, framing, and focusing the finder image is always favourably bright. This is effected by open-aperture metering on the principle of electronic diaphragm control. Moreover, the finder image is very contrasty, brillant, and very large so that it can be fully judged even under unfavourable light conditions. The size of the finder image is 95% of the real picture size, i.e. finder image and the picture to be taken will coincide in size.

Rapid PRAKTICA bayonet

One of the main features of the new PRAKTICA system is the PRAKTICA bayonet mount. Being easy in handling, this novel lens mount connects camera and lens or accessories rapidly and precisely. With the PRAKTICA bayonet it is a matter of seconds to change the lens: Insert the lens as to the red marks, give it a quarter of a turn - and the functions of automatic stopping-down as well as of electronic transmission of diaphragm values for open-aperture metering are exactly coupled. This exactly fixed position of the lens in the bayonet is also the pre-condition that the diaphragm values are exactly reflected into the finder image. The prospective PRAKTICA bayonet with its large inner diameter will give sufficient space for further developments of the PRAKTICA system without the need to change the coupling conditions.

Open-aperture metering by electronic diaphragm control

The automatic diaphragm control of the PRAKTICA B 200 is based on the proved principle of internal metering. At open aperture the diaphragm values are electronically transmitted from the lens into the computer of the camera. This results in an optimum bright finder image which is of benefit for viewing, framing, and focusing the subject as well as for taking close-ups with extension-lengthening accessories. PENTACON has world priority for this unique technological solution.

Triple wedge metering system ensures highest picture definition

Focusing is via a novel triple wedge metering system. As compared with usual metering wedges, this setting as to vertical and horizontal outlines results in an essentially increased accuracy and thus an improved focusing. The metering wedges are now surrounded by a truncated prism screen ring and a groundglass ring. These three focusing elements will pave the way to attain highest picture definition. Depending on the character of the subject choice is between both these focusing principles.

Novel metal-blade instant return shutter for precise exposure

For the PRAKTICA B 200 an absolutely novel shutter type has been designed the blades of which immediately return into their initial position when the shutter has run down (metal-blade instant return shutter). Its size and its system of electronic speed formation are best adapted to the conditions of a fully automatic compact camera. The novel PRAKTICA shutter is a reliable party to the camera electronics and distinguishes itself by its exactness, low noise and low vibration in running down as well as its resistance against influences of extreme temperatures.

The speeds cover the wide range from 40 sec. to 1/1000 sec. and, being of importance for an extremely good exposure, any incremental value can be electronically controlled, too. The shutter is synchronized with 1/90 sec. for electronic flashing. As this speed is mechanically formed it is available also for shooting without flash unit and without battery: it can be mechanically set by hand.

Up-to-date microelectronics packed on a flexible circuit board

The PRAKTICA B 200 combines modern electronics and opto-mechanical precision into a perfect system which imparts the taking technique a high degree of convenience. All the electronics of the camera with three large-scale integration circuits (LSI) is packed on one flexible circuit board. An ultramodern gallium-arsenide-phosphide photodiode is used as light receptor. The first circuit receives the input signals and converts them (e. g. signals for subject brightness, film speed, and diaphragm number). The second one treats the entered data by computing the correct shutter speed, while the third circuit controls the LED indication in the viewfinder and shutter. The entire control system is an analogue mini computer; the computed values are digitally stored. Fixed shutter speeds are entered in coded manner.

Memory key

Rapid working with full utilization of the automatics, but with individual shutter speed compensation as to the photo-graphers' intention is made feasible by a memory key (key to store the measured value). The metered light value, e. g. such resulting from close-up metering, is stored when the key is depressed so that the selected section of the picture can be accordingly altered without changing the exposure speed. This means an ideal combination of purpose-directed and automatic exposure. Besides this, the battery can be checked by this key.

PRAKTICAR-lenses: handy and versatile

Finally, not only the picture quality but also the possibilities of camera application are determined by the lenses. For this reason first-class lenses with stopping-down automatics and extraordinary optical and mechanical qualities have been designed particularly for the PRAKTICA B 200. They are an integral part of the new PRAKTICA system. We should point out the compact design and the low weight of the PRAKTICAR lenses so that the camera-lens combination remains handy and well balanced. For a convenient operation, the lenses are provided with handy knurled rings, and the knurls of the individual rings are well differentiated. Without taking the camera off your eye you are able to distinguish between the diaphragm-setting and focusing data. The multi-coating on the top lens surfaces brings about a particularly brilliant, contrasty reproduction at highest picture definition. From the most extreme wide-angle lens to the tele lens all the offered interchangeable lenses allow you to compose your picture as to your intentions, with such a versatility as it is offered by photographic practice itself.

Manufacturer description #2

With the PRAKTICA B 200 you have acquired a superior, compact 35 mm SLR camera with fully automatic shutter speed control across the entire range from 1/1000 s to 40 s. In addition, the microelectronic system of the camera lets you take pictures with fixed shutter speeds between 1/1000 s and 1 s, and exposures of any length can be made when you set the shutter speed dial to "B". Through-the-lens metering is at full aperture and thus the brightest viewfinder image, with the diaphragm values being transmitted from lens to camera in the form of electrical impulses.

16 light emitting diodes (LEDs) at the right side of the viewfinder will give you required information on essential shooting data and operations such as exposure time to be expected, limits and working stages (fully or semi-automatic). The diaphragm value is reflected into the lower edge of the viewfinder image.

The automatic system can be overridden should you desire to take special under or over-exposed pictures.

The PRAKTICA B 200 with the new PRAKTICA bayonet mount has been designed for fast lens changing.

***

SLR camera of frame size 24 x 36 mm, TTL metering at full aperture by electronic aperture value transmission.

Automatic and stepless electronic shutter speed control from 1/1000 s to 40 s.

Automatic operation switchable to semi-automatic operation; fixed speeds of 1/1000 s to 1 s are provided.

LED signals appearing in the viewfinder image indicate the shutter speed to be expected.

Limit value indication for under or over exposures.

The set stop is visible at the bottom of the viewfinder.

Manual shutter speed correction possible within ±2 speed steps.

Exposure memory system.

Focusing: Fresnel lens with novel triple rangefinder wedge, truncated micro prism screen and ground glass field; - cross metering -.

Field of view: 95 %.

Flash synchronization at 1/90 s, mechanically controlled.

PRAKTICA bayonet mount (44.4 mm bearing diameter, 48 mm ID).

Motor winder connection provided.

Memory holder at the camera back.

Battery can be checked in the viewfinder.

Power: 6 V primary battery, e. g. PX 28, Mallory.

Gallium-arsenide-phosphide photodiode used as light receiver.

Measuring and control range: 0-17 EV at 21 DIN and stop 1.4.

Selftimer with starting button, providing 8 s delay.

From the editor

Announced at Photokina 1978.

110,262 units were produced from December 1979 to August 1982.

For export, the camera was sold mainly with a chrome top plate and under the names Praktica B200 electronic or Praktica BCX electronic.

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Chromatic aberration

There are two kinds of chromatic aberration: longitudinal and lateral. Longitudinal chromatic aberration is a variation in location of the image plane with changes in wave lengths. It produces the image point surrounded by different colors which result in a blurred image in black-and-white pictures. Lateral chromatic aberration is a variation in image size or magnification with wave length. This aberration does not appear at axial image points but toward the surrounding area, proportional to the distance from the center of the image field. Stopping down the lens has only a limited effect on these aberrations.

Spherical aberration

Spherical aberration is caused because the lens is round and the film or image sensor is flat. Light entering the edge of the lens is more severely refracted than light entering the center of the lens. This results in a blurred image, and also causes flare (non-image forming internal reflections). Stopping down the lens minimizes spherical aberration and flare, but introduces diffraction.

Astigmatism

Astigmatism in a lens causes a point in the subject to be reproduced as a line in the image. The effect becomes worse towards the corner of the image. Stopping down the lens has very little effect.

Coma

Coma in a lens causes a circular shape in the subject to be reproduced as an oval shape in the image. Stopping down the lens has almost no effect.

Curvature of field

Curvature of field is the inability of a lens to produce a flat image of a flat subject. The image is formed instead on a curved surface. If the center of the image is in focus, the edges are out of focus and vice versa. Stopping down the lens has a limited effect.

Distortion

Distortion is the inability of a lens to capture lines as straight across the entire image area. Barrel distortion causes straight lines at the edges of the frame to bow toward the center of the image, producing a barrel shape. Pincushion distortion causes straight lines at the edges of the frame to curve in toward the lens axis. Distortion, whether barrel or pincushion type, is caused by differences in magnification; stopping down the lens has no effect at all.

The term "distortion" is also sometimes used instead of the term "aberration". In this case, other types of optical aberrations may also be meant, not necessarily geometric distortion.

Diffraction

Classically, light is thought of as always traveling in straight lines, but in reality, light waves tend to bend around nearby barriers, spreading out in the process. This phenomenon is known as diffraction and occurs when a light wave passes by a corner or through an opening. Diffraction plays a paramount role in limiting the resolving power of any lens.

Doublet

Doublet is a lens design comprised of two elements grouped together. Sometimes the two elements are cemented together, and other times they are separated by an air gap. Examples of this type of lens include achromatic close-up lenses.

Dynamic range

Dynamic range is the maximum range of tones, from darkest shadows to brightest highlights, that can be produced by a device or perceived in an image. Also called tonal range.

Resolving power

Resolving power is the ability of a lens, photographic emulsion or imaging sensor to distinguish fine detail. Resolving power is expressed in terms of lines per millimeter that are distinctly recorded in the final image.

Vignetting

Vignetting is the darkening of the corners of an image relative to the center of the image. There are three types of vignetting: optical, mechanical, and natural vignetting.

Optical vignetting is caused by the physical dimensions of a multi-element lens. Rear elements are shaded by elements in front of them, which reduces the effective lens opening for off-axis incident light. The result is a gradual decrease of the light intensity towards the image periphery. Optical vignetting is sensitive to the aperture and can be completely cured by stopping down the lens. Two or three stops are usually sufficient.

Mechanical vignetting occurs when light beams are partially blocked by external objects such as thick or stacked filters, secondary lenses, and improper lens hoods.

Natural vignetting (also known as natural illumination falloff) is not due to the blocking of light rays. The falloff is approximated by the "cosine fourth" law of illumination falloff. Wide-angle rangefinder designs are particularly prone to natural vignetting. Stopping down the lens cannot cure it.

Flare

Bright shapes or lack of contrast caused when light is scattered by the surface of the lens or reflected off the interior surfaces of the lens barrel. This is most often seen when the lens is pointed toward the sun or another bright light source. Flare can be minimized by using anti-reflection coatings, light baffles, or a lens hood.

Ghosting

Glowing patches of light that appear in a photograph due to lens flare.

Retrofocus design

Design with negative lens group(s) positioned in front of the diaphragm and positive lens group(s) positioned at the rear of the diaphragm. This provides a short focal length with a long back focus or lens-to-film distance, allowing for movement of the reflex mirror in SLR cameras. Sometimes called an inverted telephoto lens.

Anastigmat

A photographic lens completely corrected for the three main optical aberrations: spherical aberration, coma, and astigmatism.

By the mid-20th century, the vast majority of lenses were close to being anastigmatic, so most manufacturers stopped including this characteristic in lens names and/or descriptions and focused on advertising other features (anti-reflection coating, for example).

Rectilinear design

Design that does not introduce significant distortion, especially ultra-wide angle lenses that preserve straight lines and do not curve them (unlike a fisheye lens, for instance).

Focus shift

A change in the position of the plane of optimal focus, generally due to a change in focal length when using a zoom lens, and in some lenses, with a change in aperture.

Transmittance

The amount of light that passes through a lens without being either absorbed by the glass or being reflected by glass/air surfaces.

Modulation Transfer Function (MTF)

When optical designers attempt to compare the performance of optical systems, a commonly used measure is the modulation transfer function (MTF).

The components of MTF are:

The MTF of a lens is a measurement of its ability to transfer contrast at a particular resolution from the object to the image. In other words, MTF is a way to incorporate resolution and contrast into a single specification.

Knowing the MTF curves of each photographic lens and camera sensor within a system allows a designer to make the appropriate selection when optimizing for a particular resolution.

Veiling glare

Lens flare that causes loss of contrast over part or all of the image.

Anti-reflection coating

When light enters or exits an uncoated lens approximately 5% of the light is reflected back at each lens-air boundary due to the difference in refractive index. This reflected light causes flare and ghosting, which results in deterioration of image quality. To counter this, a vapor-deposited coating that reduces light reflection is applied to the lens surface. Early coatings consisted of a single thin film with the correct refractive index differences to cancel out reflections. Multi-layer coatings, introduced in the early 1970s, are made up of several such films.

Benefits of anti-reflection coating:

Circular fisheye

Produces a 180° angle of view in all directions (horizontal, vertical and diagonal).

The image circle of the lens is inscribed in the image frame.

Diagonal (full-frame) fisheye

Covers the entire image frame. For this reason diagonal fisheye lenses are often called full-frame fisheyes.

Extension ring

Extension rings can be used singly or in combination to vary the reproduction ratio of lenses. They are mounted between the camera body and the lens. As a rule, the effect becomes stronger the shorter the focal length of the lens in use, and the longer the focal length of the extension ring.

View camera

A large-format camera with a ground-glass viewfinder at the image plane for viewing and focusing. The photographer must stick his head under a cloth hood in order to see the image projected on the ground glass. Because of their 4x5-inch (or larger) negatives, these cameras can produce extremely high-quality results. View cameras also usually support movements.

135 cartridge-loaded film

43.27 24 36
  • Introduced: 1934
  • Frame size: 36 × 24mm
  • Aspect ratio: 3:2
  • Diagonal: 43.27mm
  • Area: 864mm2
  • Double perforated
  • 8 perforations per frame

120 roll film

71.22 44 56
  • Introduced: 1901
  • Frame size: 56 × 44mm
  • Aspect ratio: 11:14
  • Diagonal: 71.22mm
  • Area: 2464mm2
  • Unperforated

120 roll film

79.2 56 56
  • Introduced: 1901
  • Frame size: 56 × 56mm
  • Aspect ratio: 1:1
  • Diagonal: 79.2mm
  • Area: 3136mm2
  • Unperforated

120 roll film

89.64 56 70
  • Introduced: 1901
  • Frame size: 70 × 56mm
  • Aspect ratio: 5:4
  • Diagonal: 89.64mm
  • Area: 3920mm2
  • Unperforated

220 roll film

71.22 44 56
  • Introduced: 1965
  • Frame size: 56 × 44mm
  • Aspect ratio: 11:14
  • Diagonal: 71.22mm
  • Area: 2464mm2
  • Unperforated
  • Double the length of 120 roll film

220 roll film

79.2 56 56
  • Introduced: 1965
  • Frame size: 56 × 56mm
  • Aspect ratio: 1:1
  • Diagonal: 79.2mm
  • Area: 3136mm2
  • Unperforated
  • Double the length of 120 roll film

220 roll film

89.64 56 70
  • Introduced: 1965
  • Frame size: 70 × 56mm
  • Aspect ratio: 5:4
  • Diagonal: 89.64mm
  • Area: 3920mm2
  • Unperforated
  • Double the length of 120 roll film

Shutter speed ring with "F" setting

The "F" setting disengages the leaf shutter and is set when using only the focal plane shutter in the camera body.

Catch for disengaging cross-coupling

The shutter and diaphragm settings are cross-coupled so that the diaphragm opens to a corresponding degree when faster shutter speeds are selected. The cross-coupling can be disengaged at the press of a catch.

Cross-coupling button

With the cross-coupling button depressed speed/aperture combinations can be altered without changing the Exposure Value setting.

M & X sync

The shutter is fully synchronized for M- and X-settings so that you can work with flash at all shutter speeds.

In M-sync, the shutter closes the flash-firing circuit slightly before it is fully open to catch the flash at maximum intensity. The M-setting is used for Class M flash bulbs.

In X-sync, the flash takes place when the shutter is fully opened. The X-setting is used for electronic flash.

X sync

The shutter is fully synchronized for X-setting so that you can work with flash at all shutter speeds.

In X-sync, the flash takes place when the shutter is fully opened. The X-setting is used for electronic flash.

Unable to follow the link

You are already on the page dedicated to this lens.

Cannot perform comparison

Cannot compare the lens to itself.

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

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),

where:

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

Mount

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.

Speed

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. Magnification is expressed as a ratio. 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.

Weight

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.

Filters

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

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.