Olympus OM-1(n) & OM-2 (n) - Finder Group accessories
Interchangeable Focusing Screens Part 1/2


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Interchangeable Focusing Screens

Everybody who picks up a camera and shot will have a objective to record something on film. Whether it is to capture a memorable moments or in the line of duty. Not all photographers are artist - that is of sure. A camera such as any of the OM series bodies may be ended in a lab researcher's hand who is only interested getting a perfect exposed and a pin sharp picture of a micro-organism under the high power magnification microscope, a housewife who is only interested to capture her babies or an art college student whose only worry is whether the lecturers will like his/her composition etc.

There are hundreds of system accessories within the OM system that have been carefully design to meet extensive requirements and try to satisfy all level of users who may has different levels of requirements. NONE of the OM camera models is provided with an interchangeable prism/finder feature. Cost of production is one thing, maintaining continuous support and development is another, Olympus argued the functionality of such requirements which were first seen in the Nikon F in 1959 and hence all F-class professional Nikon models retain this feature as standard.

Canon also had this with their original Canon F-1 in 1971 and the subsequent upgrade in 1981 with the New Canon F-1 but eventually omitted the feature with their EOS class AF cameras. Minolta's and Pentax has only one manual focus model each that provide interchangeability of finders, that is the Minolta XK/XM in 1973 and Pentax LX in 1980.

Hey, what are all these ? What is it got to do with focusing screens and are they relative ? Not quite, but it explains how Olympus uses the finder section to offset the effect of an omission of the interchangeable prism feature provided by competitions. If you are a current OM user, you may not feel the differences posted when look through the viewfinder of any OM cameras. Primarily because you have probably get used to that and it is hard to imagine everything you see will be 'reduced' in size through the viewfinder. But for any other users (except users of manual focus Pentaxes) of Nikon or Canon, who are so used to "medium range" magnification of viewfinder image, the first experience when peeping through the eyepiece of an OM1 or OM2 camera is really quite an experience - because the Xtra LARGE image projected inside the finder is so bright and contrasty ! OM1 and OM2 bodies have an viewfinder magnification of 0.92X (at infinity with 50mm standard lens) and still able to maintain an impressive finder field view of 97% of the actual picture field !

Well, for Olympus there were almost close to 30 odd Zuiko lenses were being introduced when the OM1n was made available. To take full advantage of all these first class optics, a camera with a viewfinder that producing bright, clear images is therefore of primary importance in focusing and compositions. The OM System has always stressed the need for a big, bright finder image, and this was one of the OM-1's major innovations, So does the method of how to handle interchangeable focusing screens with a fixed type pentaprism SLR design. The OM solution was to dopt a new method of changing the screens through the lens mount.

Basically the OM system embraces everything covers from astrophotography to microscope photography, and even adds the option of endoscopy, medical application, shift and tilt lenses for architectural photography and more, clearly just one standard screen is nowhere near enough to covers all these applications.

Since OM SLR cameras have no interchangeable prism, Olympus had their top of the range SLR camera models which started from the original OM-1 in 1972 added with an interchangeable focusing feature.

Focusing Screens for OM1(n) and OM2(n) Series SLR camera models


Let's take a look at the focusing screen and its role in the single lens reflex design. In the early days of single lens reflex development the screen was a rather simple device with a matte, or ground glass surface. The early screens were diffficult to use, for to be effective in diffusing light their surfaces had to be rough. As SLR system has the advantage to view things 'directly', if the single lens reflex was to be a success, the viewing and focusing system needed improvement.

The design and its surface has been improved and refined over the years with new production technique employed, resulting in a considerably brighter image which greatly improved focusing ability. Additional focusing aids in the form of a microprism and split image rangefinder added to the center of the screen make the focusing system even easier to use and has a broader scope of general application for most lenses introduced later. Among the many types of standard focusing screens, one of the significant design was the Split image. It divides the subject in half horizontally, the split-image rangefinder works well for subjects with well-defined outlines or vertical lines. The microprism is a big help in shooting subjects having no definite contours and can be used effectively with a variety of lenses. In addition, the matte portion of the screen is particularly useful when shooting portraits or closeups, or when using a slower speed telephoto lens. The standard screen is designed for utmost versatility so as to cover a variety of subjects and situations. However, because the ideal screen can vary depending on the lens in use. and the subject being photographed, only selective 'higher end' Canon SLR cameras such as OM1, OM2, OM3 and OM4 series bodies have such provision for interchanging focusing screens feature.

The OM system has more than 10 types of focusing screens (17 to be exact). But focusing screen as a factor among all SLR advantage does not apply too well here especially where automated bodies relate. Because 'high-end" OM electronic bodies since 1975 were employed with the propriatery TTL OTF direct light measurement system where the pair of SBC metering cells (B1 & B2) which handle metering during an exposure process are situated undernealth the main reflex mirror, which locates under the focusing screen.

Another pair of Cds cell (C1 & C2) only measure light coming in from lens, reflected through the mirror and passing through the focusing screen for the exposure data display inside the viewfinder. But OM system still offer a user with a great varieties of options to cover different levels of requirements.

Thus, in a way the focusing screen for those selective OM bodies has a lesser role to play but maintaining the brightest possible transmission of light to the pentaprism for focus and composing, other than partial function of metering. But although in terms of varieties, the OM screens should be more than sufficient for anyone to enjoy better photography with the respective bodies that permit change of screens, but Olympus has not, over the years bringing out more creative screen types into the family. Some highly innovative screens such as Cross Split, lazer-matte screen types, the Type "T" ofr TV broadcating and "Type M" which has a fine-ground fresnel field with 5.5 mm clear spot and double cross hair for use in parallax focusing on aerial image, plus millimeter scales for calculation of individual magnification of objects or for measuring objects are some examples of highly innovative screen types that provide agood and usewful visual aids in focusing and composing.The current OM-3 and OM-4 can use no less than 14 types (originally, screens for OM-1 and OM-2 has 13 types but some would cummarized everything to numbered it as 17 types) of focusing screens to cater for every imaginable photographic requirements. And with the kind of thoughtfulness and one of the greatest OM advantage in this related field is, these screens were being designed to be fast and easy to change. To change a screen, simply unmount the lens, flick open the catch inside the lens mount, and the screen can be removed and replaced in seconds. Depending on the types of lenses you are using or nature of your assignment, some may even find the standard Focusing Screen 1-1 is often inconvenient or difficult to use. With super-telephoto lenses for instance, the microprism becomes excessively dark. With the high magnifications of macrophotography and photomicrography, it may even be impossible to focus. With interchangeable screens, one can find the particular type of screen that best suit the type of photography or individual needs.

Note: The Focusing Screens 2 can only be mounted in the OM2SP, OM-3(Ti) and OM-4(Ti). The clear-field type focusing screens provide brighter viewfinder images. However, with the OM1(n) or OM2(n) bodies, metered needle in manual does not give correct light readings. With the OM-2(n) on Auto the needle does not point to the precise shutter speed but correct exposures are made on the film. With the OM2SP, OM-3(Ti) or OM-4(Ti) the clear-field type focusing screens give correct light readings.

Changing Focusing Screen Focusing screen is supplied singly and it comes with a tweezers. This allows the focusing screen to be gripped securely without touching the surface when fitting it through the lens mount of the camera.

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Caution: This procedures may demand a safe and experience photographer to perform the task, although the system Olympus designed was with user friendliness in mind, but if you are not too familair with changing the screen yourself, please handle with extreme care.

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The OM System Focusing Screens provide you with a high level of in focusing versatility. There are optional Screens available to suit practically every picturetaking situation. The optional Focusing Screens come with a special tool.

To remove the Focusing Screen:

1) Insert the tool into the camera and pull on the release catch. This allows the Screen and screen frame to drop down.
2) Using the tool, the Screen can be made to drop completely down without touching it. Remove the Screen by gripping the plastic tipped portion of the Screen between the tool's jaws with light but firm pressure.
3) For installing the Screenóreverse the above procedure.

<<<<--- Older versions of Focusing Screens. PDF Format (184k)

IMPORTANT: Although the above procedure could be done with fingers, the use of a pair of tweezers is a must, because changing Focusing Screen is a procedure to be handled with great care. Trying to change Screens with your finger can result in fingerprints and costly damage to the surface of the Screen. Should this occur, cleaning or repair MUST be handled by an authorized service center.

* If there is dust or dirt in the viewfinder, use an air blower to remove it. Never wipe the surfaces of the screens, prisms, or mirror with cloth or paper.
* The meter needle does not indicate proper exposures for manual exposure photography when the 1-5,1-6,1-7, or 1-9 Focusing Screens are used, although they produce an extremely bright viewfinder image. Proper exposures are obtained with these Screens in automatic photography, however, the shutter speed scale in the viewfinder does not give an accurate indication of the actual shutter speed used during exposure.

The 14 interchangeable focusing screens make up the core of the Finder Group (12 types were available during initial stage and two more were added in later stage). Other units include the Varimagni Finder, etc. The feature of each Focusing Screen is listed at sections that followed.

Note: The 1-5, 1-6, 1-7 and 1-9 are not used with the exposure meter built in the camera. <<< --- Focusing screen form an OM-1n and a OM-4 look identical.

The 1-3 and 1-13, 1-14, suitable for general photography, are particularly advantageous when taking a subject with vertical or even horizontal lines (1-14). The 1-5 is ideal for the snap-shooters using a wide angle lens. The 1-4 and 1-7 are designed for super-telephoto lenses and 1-4, 1-11 and 1-12 are for close-ups, macrophotography and photomicrography. Basically, accessories found in the Finder Group such as focusing screen is to enhance and provide an optimum image visibility in broad range of lighting condition. During the early days when the OM-2 was introduced, there were a choice of 12 interchangeable focusing screens to supplement lenses of every focal length including special purpose lenses, telescopes, endoscopes and microscopes.

Since NOT all OM bodies are employing with similar exposure measuring methods, in the case of the OM-1 where the metering cell is located near the eyepiece, while the OM-2 has two pairs of Cds and Blue cells to handling exposure reading and for actual exposure reading light reflected from the film plane; thus, theoritically, exposure indication inside viewfinder is only serves as a reference guide but actual exposure could varies from such indication. Huh ? yeap, other manufacturers employ a memory storing method and margin for error in extreme of exposures could even be higher than the OM method. WHY does it matters ? Oh.. take the case of the OM-1 and OM-2, if you were to put a focusing screens design and made for the OM-3 (there are brighter than earlier screens and some OM users actually modify the tab on the screen to make it fit into earlier bodies..), exposure compensation may be required for the OM-1, since exposure reading are through the lens and screens and only meter at the eyepiece; however, in the case of the OM-2, the blue cells at each side of the mirror box, facing backward towards the film plane are the pair that actually command the exposure to be made, and in theory no expsoure compensation is required.

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Olympus OM-1(n): Main Index Page (5 Parts) | Camera Operations (6 Parts)
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Olympus OM-2SP: Camera Operations | Other Issues
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Motor Drive and Power Winder: Main Index Page (4 Parts)
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