When I bought this NPS Close-up accessory for Praktica (with tripot?) it came with a much folded set of instructions. The paper was huge—10 x 17 inches—and my scanner deck will only take 8 ½ by 11 inch pages. The many, many creases didn’t bode well for reproduction. So I spent most of an afternoon doing optical character recognition on the instructions and making scans of the multiple bits like equations and tables.
So here we go—
Extension Tubes
The extension tube's function is to provide an additional variable amount of extension between the lens and the camera body. This added extension becomes necessary when an increase in the focusing range of the camera lens is desired, as in close-up photography. The extension tube may also be used to adapt long focus lenses to the camera body and provide the proper extension and (with the focusing extension tube) for focusing such lenses.
Using Extension Tubes With Lenses Fitted For The Camera
Any lens made for a specific camera has a fixed focusing range which is limited by the amount of travel provided by the lens barrel. This range varies according to the individual design of the lens barrel, but generally 50 to 58mm normal lenses have a range from between 1½ and 3 feet to infinity and 135mm lenses from about 5 feet to infinity. When it becomes necessary to focus closer than the near limit of these lenses, the use of extension tubes is required.
Attaching The Extension Tubes
The extension tube is placed between the camera lens and the camera body, in the same manner in which the lens is inserted into the camera. The tube set consists of various size tubes which may be used individually or in combination. The extension tube sets for EXAKTA and PRAKTINA include the appropriate male and female bayonet adapters.
Fitting Exakta Accessories
Occasionally. there is a need to adjust the fit of accessories that bayonet into the Exakta body. This need for adjustment in no way indicates any defect in the camera or accessory, since only slight variations arise not only in the camera body but in the accessory as well.
To permit ready adjustment, the manufacturer of the camera, as well as the manufacturer of the accessories, have put thin slits behind the bayonet flange so that the flange can be depressed or lifted for perfect fitting.
It is suggested that all adjustments be made on the accessories, since the initial adjustment on the camera is made at the factory and presumably accepts the normal lens property,
To Adjust the Fit Between the Camera Body and the Male Adapter of the Accessory:
This is the most frequent adjustment required.
When the accessary fits loosely into the body of the camera, the flanges of the accessory (male bayonet adapter) must be depressed so that they sit tightly against the (female) bayonet in the camera. The flange of the accessory may be depressed by simply pressing the flange down on a hard surface, the closing the slit behind the bayonet.
If the accessory fits too tightly the flange may be opened by inserting a thin knife blade into the slit to expand the slit.
If the accessory can not be turned clockwise to the lock position (but will turn counter clockwise), the pin of the accessory flange is hitting the outside bayonet of the camera body flange. The pin may be filed a little thinner so that the clearance between the pin and the accessory flange is increased.
All adjustments described are very minor—only the slightest change is generally required to provide a perfect fit.
If you are unable to make the adjustments described, contact your dealer, describing your fitting problem in detail so that be may have his or our Adjustment Department make the needed adjustments for you.
Exposure
Exposure is determined by the proper combination of shutter speed and f/stop (diaphragm) stop, The shutter speed, of course, remains unchanged by the addition of the extension tubes but the f/stop value varies with the amount of tube extension. The f/stop value of the lens is calibrated, and is completely accurate only when the lens is focused at infinity. In normal camera use the error in the f/ stop resulting from the extension of the lens when focused at distances closer than infinity can be ignored since it is minor and is well within the range of the film's latitude. With a tube, the lens is extended beyond the point at which exposure compensation can be neglected, making it necessay to apply the proper exposure correction factor. The following tables show the exposure factors for the most commonly used lenses and are self explanatory. The required exposure increase (exposure factor) is applied in the same manner as a filter factor. Thus, a factor of 2x requires a larger opening of one f stop or twice as long a shutter speed, a factor of 4x requires a correction of 2 f stops. and an 8x factor requires a correction of 3 f stops.
A simple method for correcting exposure with any known factor is to divide the ASA speed value of the film by the exposure factor; then the meter will automatically compensate for exposure factor.
Exposure compensation can also be computed by determining the Effective f/ value (Ef/) as contrasted with the Indicated f (If) value. The general formula is:
(Insert formula jpg)
Therefore the actual f/8 setting is equivalent to f/16 and it is necessary to determine the proper shutter speed for f/16 rather than f/8. Simply read the shutter speed setting opposite f/16 on your exposure meter and you will have automatically corrected for the required 4x exposure increase which the table indicates as necessary in this example.
The Focusing Extension Tube
The function of the Focusing Extension Tube is to provide a continuous varying extension over a limited range. The focusing tube is similar in design to that of the normal lens barrel which provides the variable extension required to focus the lens. The Focus Tube provides an extension range of 15mm, from 40mm to 55mm approximately. The Focusing Extension tube is invaluable in supplimenting the normal extension tube set, and in using the special short mount lenses designed for use with Bellowscopes and Focusing Tubes; and for adapting long focus lenses.
The ACCURA special short mount 105mm and 135mm lenses when used with the Focusing extension tube will provide a focusing from infinity to as close a distance as you wish, depending on the number of tubes you add to the focusing tube.
Adapting Long Focus Lenses
Since long focus lenses, from large cameras, can often be purchased very reasonably or may already be part of the photographer's equipment, it may be desirable to adapt such lenses to the 35mm camera. The Focusing Extension tube provides an ideal device for such an adaptation. The method of attaching the lens to the tube can usually be simplified by the use of a camera body cap for a particular camera and by utilizing this body cap as a lens board in the Focusing Tube. Some lenses are too large in diameter to permit mounting into a body cap in which case special adaptation is required.
Bellowscopes
Bellowscopes are similar in function to the Focusing Extension Tube and will be selected when greater extension than is provided by the tubes is required. They also have the unique property of providing a complete and continuous focusing range from infinity to approximately 10 inches with the 105mm and 135mm short mount lenses,
Data for 50mm lenses
Data for 58mm lenses
Data for 105mm lenses
Total Depth of Field in MM
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