The possibility of obtaining photographic images without lens attracts many. One interesting to try a new tool for obtaining new visual effects, the other in itself a physical experience. Some naive and simple image obtained by this ancient method, has a strong aesthetic impact, and someone is willing to shoot pinhole camera just for fun. If you alien naive art (primitive), if you aspire to maximize accurate representation of reality, if the desire for creative experimentation, you do not understand – the shooting of the camera obscura is clearly not for you. Otherwise, you should definitely try. Who knows, could this direction will help you to reveal themselves fully.
In Russia shooting obscura did not become popular. Referring to the traditions piktorealizma, Russian photographers often use a monocle (of single-lens), often by manufacturing it from the old lens “Helios”. In foreign countries, however, wants to withdraw aberration of the optical system, above all, appeals to obscura (murals), the camera with a tiny round hole instead of the lens.
Device obscura very unpretentious. Of course, you yourself can easily come up with some original designs. Describing his own version here, I just want to share their experiences. Acquaintance with him will allow you, on the one hand, without thinking about the theory, it is easy to repeat it, but, on the other hand, may induce you to carrying out their own ideas.
A hole-mount TO
I made a pinhole lens for its products as a standard mount for SLR cameras to Pentax. We will not go into academics debate whether you can take a simple round hole lens. For simplicity, we assume that the term “lens for pinhole” is used here only for convenience.
Making a pinhole-based SLR camera has several positive aspects:
1. You can easily direct the camera to the object and crop the image. In bright light it can be done by simply looking through the viewfinder. If the shooting subject is bright enough, you can at the moment proposed to replace the traditional optical lens product with an equivalent focal length and, after the framing is done, once again turn their reflex camera obscura in.
2. In most cases you can use staff eksponometricheskim device SLR camera to determine exposure, which is more than comfortable. We must not only forget about the need in some cases, exposure correction.
3. You do not have to think about how to install the camera obscura on a tripod. This can be done for traditional SLR method.
4. For recording, you can use an ordinary film 35 mm (Type 135). And one part of the frames can be made of conventional lenses, and other obscura.
5. You can also try using a multiple exposure mode (for those cells where it is) and expose the same frame beginning with a normal lens, and then replace it with a pinhole aperture to create special effect.
The most significant disadvantages of this design:
1. Shooting is conducted on a flat frame. Therefore, in order to avoid vignetting equivalent focal distance of mirror pinhole must be sufficiently large.
2. Make a wide angle camera will not work, even if we are satisfied with the strong vignetting. This is due to the inability to bring the hole to the film at a sufficiently small distance.
3. Resolution of the camera obscura is small, so expect a large increase when printing from a narrow screen shot should not be.
Made my design shown in the photo. It consists of the following parts (from bottom to top):
1. Extension tubes № 1 Pentax, imparting the whole structure compatibility with bayonet K.
2. Click Adapter Ring Pentax K mount lenses to M42 threads (not visible in the photo).
3. Extension tubes number 2 for cells of type “Zenith”.
4. Flat cardboard collar (washer) with a diameter of 46 mm. With a central hole with a diameter of about 8 mm (not visible in the photo). To reduce internal reflections ring made of black cardboard.
5. Aluminum foil, tightly compressing the cardboard washer to the extension ring. In the center of the foil has a round hole diameter (d) about 1 / 3 mm.
The foil is attached to the ring with electrical tape. In addition, two pieces of tape to cover up the possible access of light inside through cracks in the adapter (see photo).
Engineering survey
1. In most cases, do not neglect high-speed film. Her grit and even great, but quite acceptable to take a camera obscura, which provides more than a modest resolution.
2. Since the exposure at such a small aperture will be large, it should always be used when taking a tripod.
3. For metering is quite possible to use the internal meter SLR, bringing in his testimony necessary amendments. When measuring eyepiece viewfinder should be covered with a special cover that came with the camera MZ. Setting this cap keeps out stray light on eksponometricheskoe device through the eyepiece. It should also take note that when using neavtofokusnyh lenses, which should also include the device in question, some cameras MZ automatically directed to the center-metering. Because of this and some other features, use the internal meter may hold to underexpose. A more precise way (if at all in relation to the pinhole can use the word “exact”) described in the following paragraph.
4. If you use the method described in Section 3. difficult, it should be to measure to replace the same device branded lens and Carry in Aperture Priority mode for F22. The resulting exposure time should be increased 91 times. As in the previous case, when measuring should establish a special cover on the eyepiece viewfinder. Although this is a more accurate way, but it also requires the introduction of amendments.
5. A few words should be said about the exposition amendments related to the Schwarzschild effect. Modern photographic permit exposure without taking into account this effect at up to 1 second. From personal experience I can say that in most cases, no amendment is not required until the extracts in 10 seconds. With longer exposures must multiply the time of exposure to the correction factor (see table). Data in the table are approximate. For a more detailed and accurate information should refer to the documentation manufacturers photographs.
6. But to have confidence in the calculated value of exposure is impossible. All equipment photography pinhole camera linked with approximately and large errors. Therefore the use of bracketing should be the rule rather than the exception.
7. In the first rough approximation when taking the camera obscura can use the rule, known in English literature as «sunny 16″. In general, the rule is: if the survey is carried out on a sunny day, the aperture should be set equal to 16, while an excerpt of seconds must be equal to one divided by the film speed in units of ISO. For consideration in this article with a pinhole aperture f/210 this rule transformed into the following recommendation: if you use a sunny day ISO 400 film exposes it for 0,5 seconds.
About Technology
Despite its apparent simplicity, making obscura requires certain knowledge and skills. Sophisticated experience pundits argue about the materials, manufacturing technology openings, the thickness of the foil, emulsions and many other things. But all this is the aerobatics! For a start it is possible to confine ourselves to simple materials and technologies.
The hole can be done in cardboard, but the benefits are undeniable foil. Very thin foils choose not to be. As in all things, has its own optimum. But discussion of such subtleties is beyond the scope of this article.
Get smooth hole is easiest to use a regular sewing needle, or rather its tip, as the maximum diameter of even the thinnest of needles over 1 / 3 mm. To the needle does not penetrate through the foil at large than the required depth, can be strung on it simply limiter from a piece of eraser. Preferable to avoid making a hole in one movement. The correct approach requires to make a tiny hole, and then gradually expand it in a circular motion needles. During this operation, it is desirable to place the foil between two pieces of thick paper.
How to measure the diameter of the resulting hole? To this end, I have made on a laser printer just a ruler, the strokes followed by a 1 / 3 mm. The control measure I do with this ruler and magnifying glass. The accuracy of this method is quite satisfactory.
Note:
How can I be sure that the most frequent strokes followed it through 1 / 3 mm? Very simple! To do this, shown in Figure line should continue right so that the number of strokes, following through every inch of it was more. Well, let’s say, it is necessary to extend the range up to 20 cm then have it printed on a laser printer and attach to the quality of the line, which has millimeter strokes. If for every 20 cm millimeter strokes in the line will coincide with the printed, it means that everything is OK: the most frequent strokes separated by a 1 / 3 mm. If strokes over 20 cm start to diverge, it is necessary to slightly adjust the scale of print. Using the method of trial and error the desired result can be achieved fairly quickly.
You can also use a magnifying glass instead of the flatbed scanner. Foil with braid and described line should be placed on the scanner glass and the screen resolution of 600 dpi. In the image obtained (see figure) can be judged on the size holes with more than a reasonable degree of accuracy.
Indirectly estimate the size of the hole is with a meter SLR. First, you must set it firm and make an objective measurement of exposure for the aperture 22 (aperture priority mode). Then, replace the lens on the firm under review and re-metering. As noted above, the difference in meter readings should be equal to 6 – 6.5 degrees. (Here it is useful to recall once more the need to close the eyepiece viewfinder cap for metering.) Do not be surprised if the real difference will be slightly less (eg, 5.5 degrees). As mentioned above, the internal light meter may err on the side underexposure.
Short theoretical background
In conclusion, we present a brief theoretical information relating to the pinhole. I have deliberately not told about them in the very beginning of the article so as not to scare readers focused on the empirical knowledge of reality.
First, we list the characteristics of the optical system.
1. Obscura is characterized by an infinitely large depth of field. Bridging of the sharpness is not necessary. Talking about the focal length of a pinhole can only conditionally. Under the equivalent focal length of this camera is usually understood the distance between the hole and photographs. Angle of view pinhole can be calculated from this equivalent focal length, the standard formula for the lens.
2. Obscura creates an image without distortion, ie, without geometric distortion.
3. But the chromatic aberrations in such a system is very high.
4. In general, the camera obscura creates an image, characterized by soft, low contrast and low resolution.
5. Given these properties, when shooting pinhole camera is often used in black and white photographs. In some cases useful to use color filters.
Based solely from geometric considerations, we can conclude that the smaller the hole, the greater the resolving power of the camera. However, in reality is not so simple. With decreasing hole come into force on the diffraction limit, negate the gain in a purely geometric definition. The formula for calculating the optimal diameter of the aperture of the camera obscura was obtained by a relay:
Photos
In the left picture to determine the estimated result of the shooting narrow screen obscura on color film.
Photographs taken obscura, can also be found, for example, in the galleries of the site Worldwide Pinhole Photography Day. Organizers of this site shall open the annual exhibition of photographs. Among the participants are photographers from around the world. Russia is not yet one …