مبادىء الضبط أو التعيير .. اختيار الآلة الفوتوغرافية .. كتاب التصوير الضوئي

Principles of adjustment or calibration .. Choosing a photographic device .. Choosing and using materials .. The book of photography

Principles of adjustment or calibration:

The images of the simplest photographic devices do not need adjustment or calibration: the lens is calibrated at a certain distance (usually 3.50 meters), which means that those of small dimensions are clear enough from a distance of 1.80 meters to infinity. Indeed, all devices can be used with a fixed calibration, but it is clear that the images have better clarity if the calibration is adjusted to the exact distance of the subject, especially if the lens has a large aperture. The simplest method of calibration is the distance scale placed on the lens, which contains symbols suitable for classic amateur photographs: half-length, group, landscape. The double rangefinder (see page 35) is much more accurate than the eye's estimation of distance.

Whether single or double lens reflexes allow calibration on the objective lens which in turn is completed by a precision device such as a stigmometer or microprism (very small prisms) and we often have the choice of several mounting methods. Choose the method that suits you

If you want a light camera with no other lens than the normal focal length, the 35 has a distance measuring device that will suit you. It is absolutely useless to buy a 24 x 36 reflex (heavier and more expensive). Of course, if we do not intend to use all the possibilities that the additional parts and interchangeable lenses offer you. At first glance, the double lens reflex (size 6 x 6 cm) seems to offer no advantage other than its well-sized objective: it is heavier and less widespread than the single lens reflex. It is prone to errors, parallax and viewing images sideways. However, it must be admitted! It is a solid model of machine because of the small number of moving parts in it - and it gives excellent pictures and is less expensive than a single-lens reflex of the same size. In fact, many amateurs and professionals use it for ordinary work except for large images. One model is equipped with a pair of interchangeable lenses.

- Objective lenses:
The maximum aperture and focal length are indicated on the front of the lenses, but the power is not indicated. In general, large apertures are more expensive than normal apertures. An open lens - for example, at F1.4/1 is not as good when its pupil is set at F5.6, for example, as is the quality of a F2/2 set at the same aperture. If we look at the price and weight of a large aperture lens, we notice that it has no return except when capturing many scenes in poor lighting conditions.

With reflex machines, we aim and frame at the largest aperture of the lens, and the larger the maximum aperture, the brighter the image will be, but this is not a sufficient reason to always use a large aperture that you may not really need. Interchangeable lenses are usually mounted either in a loveseat or in a sheath. This latter mounting is often specific to each type, while a screw-mounted lens can be used directly on cases of different types.

- Instant cameras:
There are several sizes of cameras and films for instant photography: This size - square or rectangular - is sufficient for direct observation of the image. The smaller the size, the lower the price of the image (square size). Folding cameras are smaller than the one-piece models made of plastic, but they are all equally large. Most models have automatic exposure after adjusting the screen wall according to the speed of the black and white or color film. There are also models with manual adjustment. In good models, the adjustment is made either by a distance measuring device or by a reflex device
with the utmost precision. Some films require a minute to develop and this time is monitored by a timer located inside or outside the machine.

Most modern models of instant cameras use film that develops by itself in about 8 minutes without any manual work: the film is automatically removed from the box after the picture is taken and the image appears slowly in the light. For all models, a flash is used when the available lighting is sufficient.

- Exposure measurement methods:

The simplest machines are only suitable for taking pictures on negative film outdoors if the weather is good or with flash.

To work on reversible film, you must be able to make an accurate exposure measurement and then transfer it to the adjustable lens and/or shutter speed regulator. We can try to use tables explaining the exposure time, but they only give measurements for specific conditions of a given film speed: the best thing, without a doubt, is to use a pseudo-exposure time measurement device (independent or built-in) see pages 46-37. Among these independent devices, the best device is the one that gives a direct measurement without the need to transfer a first value to a computer disk. The pseudo-internal device is usually fixed and the sensitive cell or cells are placed behind the lens (in a pentaprism or behind a semi-transparent mirror), and the instructions it gives are good whatever the conditions of use of the device and lenses.

The pseudo-internal device, as we have seen, measures and sees the area of ​​the image (relative, total or optional measurement). The method used is not important as long as you know how to use it accurately.

- Automatic exposure machines: As for the 24 x 36 reflex machines, they provide automatic exposure in two ways: either by automatic aperture or by an electronically controlled automatic shutter. The first principle with pre-selection of speed uses the usual shutter speeds and gives the puzzler the appropriate aperture. As for the second principle with pre-selection of the aperture, it requires a prior announcement of the aperture on the puzzler ring and it is the puzzler that acts on the shutter mechanism to let it give the appropriate speed to illuminate the subject. Automatic aperture-first photographic machines are spreading more and more. The automatic machine gives a long pause (up to 10 seconds and more) and all medium speeds up to 1000/1 second long (even instead of the usual and international speeds - 125/1 - 250/1 - 60/1 ... etc. It is very useful to know what speed the automation has chosen.

Usually this speed is announced (by a needle moving in front of a ladder) inside the lens and finally it is always possible to stop the automation and work with manual calibrations for unusual images.

Some machines do not include a light measuring device (bosomer) so we use an independent device.

Some machines have a bosomer in the attic but it is not linked to the rest of the calibrations (film speed - speed - aperture)

Most single-lens reflex machines include a bosomer linked to the rest of the calibrations. This light measuring device is placed behind the lens.

Some automatic machines have a speed selected in advance. When the shutter speed is announced, the bosomer determines the pupil opening automatically.

For For automatic machines with pre-selected aperture, the automation device determines the shutter speed after the aperture has been set.

For some instant release machines, simply pressing a button is enough to get an image that appears without any intervention in about 8-10 minutes.

The simpler instant release machines use films containing the necessary materials for the development that immediately follows the film exiting the machine.