Modern Classic SLRs Series :
Nikon F - Operating the FTn Meter Finder/Prisms


Meter Needle.gif (8k) Viewfinder.jpg (11k)

The Photomic FTN uses a center-weighted through-the-lens metering system that reads the light over the entire focusing screen but favors the central portion of the screen. This means that it is possible to get correct exposure in situations where an averaged reading of the entire screen would result in underexposure of the main subject-with strongly backlighted portraits, for example. And since measurement is always done at full aperture with Auto Nikkor lenses, the viewfinder image is bright and clear. The amount of light reaching the film (exposure) is determined by a combination of lens aperture and shutter speed. Since the two are interrelated, different combinations will give the same amount of exposure. For example, 1/500 second at f/2 is the same as 1/30 second at f/8. The choice of aperture and shutter speed depends on the results desired. Choose a fast shutter speed to "freeze" motion, a slow one to create deliberate blur. Use a small lens aperture for wide depth of field or a large one to make the main subject stand out and throw unimportant background out of focus.

Centering the Needle
The correct exposure is found by centering the meter needle, either in the V-shaped notch which is visible in the viewfinder or at the central mark located beneath the window on top of the finder. Turn either the shutter speed selector or lens aperture ring until the needle is centered. For fine adjustments of less than one f/stop, use the lens aperture ring, since it provides reliable imtermediate settings between the marked f/numbers. The shutter speed selector is not set for intermediate values. As an added convenience, the shutter speed in use appears in the viewfinder, so the shutter speed can be adjusted while observing the exposure meter needle. In dim light, the accessory Photomic Illuminator DL-1 illuminates the meter needle and shutter speed for easy reading. Under extremely low light conditions, the meter needle may center at the "B" setting on the shutter speed selector. If so, the correct exposure time is two seconds. If the needle centers at "T" exposure time is four seconds. If the needle cannot be centered or still moves erratically after all possible aperture-shutter speed combinations have been tried, then the light is too bright or too dim for the meter. The meter's effective range (coupling range) varies according to lens used and film speed. For example, with the 50 mm f/1.4 lens and film rated at ASA 100, it extends from f/1.4 at 1/2 second to f/11 at 1/1000 second. Note: If the meter is exposed to bright light at below-freezing temperature, it may malfunction or cease to operate until the temperature rises again. Therefore, be careful not to leave the meter turned on for more than three minutes at a time in cold weather.

Getting the Right Exposure The central part of the focusing screen should always be aimed at the main subject when centering the needle. Otherwise unimportant bright or dark areas may influence the exposure reading. If an off-center composition is desired, first measure the light striking the main subject and set the aperture and shutter speed to center the needle. Then move the camera until the desired composition appears in the viewfinder. For subjects of uniform brightness, a reading may be taken from any part of the subject. However, if the subject is contrasty (sidelighted portraits, for example), measure the light falling on the most important part of the subject in which detail is desired in the final picture. For landscapes including large areas of sky, tilt the camera downward during measurement or fill the center of the finder with the main subject to prevent overexposure caused by the bright skylight, otherwise the main subject will be underexposed.

Tips: Keep Out Stray Light

The Photomic FTN Finder is designed to minimize the effect of light entering through the finder eyepiece under normal picture-taking conditions. However, in the following situations the use of a finder eyecup is recommended to insure complete exclusion of stray light.

When the needle on top of the finder is used to determine exposure, the eyepiece should be covered with the hand to prevent extraneous light from entering the finder. Measuring the bright area in the center of the screen will cause underexposure of the main subject. For correct exposure, first measure the light striking the main subject, then compose and shoot.

Measurement by Stop-Down Method Some older lenses and accessories with full-aperture exposure measurement is not possible, either because the lens has no auto-diaphragm or because the diaphragm will not couple with the Photomic FTN meter. Therefore, the stopdown method must be used. This means measuring exposure with the lens aperture diaphragm stopped down to the taking aperture. With the Photomic FTN finder, the meter coupling pin must first be pushed up into the finder so that the red index on the maximum aperture scale springs to f/5.6. Mount the lens or lens/accessory setup to the camera and switch on the meter in the usual way.
Bellows Focusing Attachments, Extension Rings and Focusing. To determine exposure, select the desired shutter speed and stop down the lens manually until the needle centers.

Note: Since focusing may be difficult or impossible at small apertures due to image darkening on the screen, first open the lens to full aperture to focus. Then determine the correct exposure by the stop-down method.

Special Lens-Focusing Screen Combinations

Screen.jpg Exposurecompensate.jpg

Because the light-transmitting properties of some focusing screens differ from those of ordinary screens, certain lens screen combinations require exposure correction to compensate for the influence of the screen. Compensating marks from -2 to +1/2 are engraved around the ASA film speed dial. With the Photomic FTN meter, exposure compensation is automatic at all aperture settings when the proper mark on the ASA scale index ring is set opposite the film speed dial. If exposure correction is required, line up the proper marking opposite the number corresponding to the film speed. When no exposure correction is required, the ASA rating for the film m use should appear opposite the red triangular index.

* Important: For complete Special Lens-Focusing Screen exposure correction/combination working with older * Nikkors, consider download a copy (448k) of the .pdf file/chart extracted from the operation manual of the FTN prism/Finder. (As this is only possible to detail the info in pdf and HTML version is NOT provided even in the FTN manual at the main page, secondly, I doubt very much there are as many users still using these older Nikkors on a FTN, neveretheless, I still provided the page as an archive - should you need them).

Repro-Copying For originals such as photographs which have tonal gradations, exposure is determined in the usual way. In the case of originals having strong contrast and no gradation, such as documents or line drawings, measure the brightness of the white portion of the original (if the original is predominantly black, a sheet of white paper may be substituted) after decreasing the film speed by four marks. Or open up the lens about 1-1/3 stops.

Slide Copying For originals with continuous tonal gradations, determine exposure in the usual way by the stop-down method. To copy slides with letters or figures on a transparent background, decrease the film speed four marks, or open up the lens about 1-1/3 stops. In the case of transparent
figures or letters on a dark background, either increase the film speed five marks or stop down the lens about 1-2/3 stops.

Fisheye-Nikkor Auto 8mm f/2.8 Because of its wide picture angle (180°), the Fisheye-Nikkor is susceptible to inflated exposure readings due to direct sunlight. To compensate, open up the lens two stops. Important: The above are only approximate guidelines. Exact exposure determination is extremely difficult, especially with reversal color films. Therefore, it is advisable to make several different exposures for each subject to be sure of getting one that is correct.

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The FTN section is my little contribution to Michael Liu's Nikon F site.

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Copyright © 1998. Michael C. Liu ®

Site rearranged by: leofoo ®. Credit: Hiura Shinsaku® from Nikomat Club of Japan for feeding some useful inputs on the introductory page. The great 3D logo by Kiasu; Ted Wengelaar®, Holland for his continuous flow of input of early Nikon bodies. Stephen Gandy's Cameraquest; Marc Vorgers from Holland for his additinal images on Nikon F Apollo; Hayao Tanabe corrected my Red Dot and Early F assertions. Gray Levett, Grays of Westminster publishes an excellent monthly historical look at Nikon products, from where I learned about the high-speed F's. Made with a PowerMac, broadcast with a Redhat Linux powered server.

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