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Сообщение от SVKan
А логика простая: что нужно. то включается.
Подсветка имеет определенную ориентацию, соответственно для разных точек требуется разная ориентация.
То бишь если подвечивать например стену в темноте, то видно, что подсветка не сплошная, а полосами. Причем диапазон полос может быть или узким (по центру) или широким.
Датчики могут быть горизонтальными, вертикальными, крестовыми.
В зависимости какая ориентация у датчиков - аналогично должны быть направлены и полосы подсветки, кроме того для подсветки центральной точки подсвечивать всю область охвата крайних датчиков...
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Хмм... "что нужно. то включается". То, что Вы описали, это и так понятно. Меня и интересовала конкретика а не общие теоретические данные.
Если бы Вы например написали, что в комбинации 580ex/20d при выборе правой верхней точки фокусировки загоряются два верхних диода подсветки, прорисовывающие горизонтальные линии в двойном количестве и при этом нижний диод, ответственный за вертикальные линии не включается и потом объяснили почему это именно так, и так далее для каждой конкретной точки фокусировки, то я бы оценил это.
Вот например ниже вставляю текст, где товарисч конкретно расписывает какой диод при каких обстоятельствах вступает в игру для комбинации 550ex/300d. Все очень конкретно и понятно:
The Canon Speedlite 550EX flash unit is capable, under camera control, of projecting various patterns of red lines on the scene upon which the camera can focus under low-light conditions. This is referred to as the "AF Assist Beam" feature.
I recently decided to learn a little more about this through inspection and testing, with the flash mounted on my EOS-300D. Some of my findings are truly fascinating.
There are three focus assist projectors on the 550EX, all located beneath the lower red "lens" on the front of the unit. One projector is at the bottom. If we look at the lens cover, we see a circular lens array. The other two projectors are side-by-side above the first one. For each of them, we see a rectangular lens array.
Note that as I describe the pattern projected by each of the three projectors, I do not attempt to give a size in terms of fraction of the frame or which focusing points are covered. That of course varies with the focal length of the lens in use. (I will make some comments on "coverage", predicated on specific focal lengths, later in this report.)
By way of an alert, let me mention here that not in each case are all three projectors activated. I will cover this at length in a little bit.
The lower projector projects a circular-outline pattern of sharply-defined vertical lines, accompanied by a second similar pattern, slightly less bright, lower in position and overlapping the "main" pattern by about half its diameter. The "main" part of the pattern is centered on the center focusing point (if we are at a distance such that parallax is of no consequence). At a distance of about 2 feet, the "secondary" part of the pattern is centered.
Each upper projector projects a pattern of three groups of four horizontal lines each. The lines are not quite as sharply defined as for the lower-projector's pattern. The bottom line of each group of four is wider than the others. The groups are separated by a space about the same width as a group.
The two such patterns are offset vertically so they interleave, forming a joint pattern of six groups of four lines, with essentially uniform spacing between all 24 of the lines. The widths of both pattern components are essentially the same, giving an overall rectangular envelope to the pattern. The leftmost projector (as reckoned from behind the camera) is responsible for groups 1, 3, and 5 (counting from the top down), the rightmost projector for groups 2, 4, and 6.
Which projectors are activated when AF assist is needed depends on the focusing point selection in effect in the camera. Here is how it works with a 300D:
If no focusing point is preselected (the "all points" condition), then, when focus assist it needed, all three projectors are activated.
If the center focusing point is preselected, only the lower projector is activated, giving the small "double-round" pattern of vertical lines. This pattern falls on the center focusing point, and there would be no benefit to also have the rectangular, horizontal line pattern in force.
If one of the four "side" focusing points is preselected, then only the two top projectors are activated, giving the rectangular pattern of horizontal lines. It is suitable for any of the side focusing points, whose detectors are most alert to horizontal lines. The circular pattern from the lower projector is not needed, and would not (at any modest focal length) cover any of the side focusing points anyway.
If either the top or bottom focusing points is preselected, no AF beam projectors are activated. The circular pattern from the lower projector would not (at any modest focal length) cover either of them, and the rectangular pattern produced by the upper projectors, being composed of horizontal lines, would be of little value, since the detectors for those focusing points are most alert to vertical lines.
This of course raises the question, "of what use is the full height of the rectangular pattern?" The answer, for the 300D or 10D, is "none". But of course other EOS cameras have focusing points "off the horizon" whose detectors are (I believe) sensitive to horizontal lines.
What about the width of the rectangular pattern with respect to the frame and the focusing points? Basically, at a focal length of 24 mm, the width of the pattern just about embraces all the "on the horizon" points. Very primitive testing suggests that, with the leftmost or rightmost focusing point preselected, reliable focusing can be achieved, based on the AF assist pattern, at a focal length of 28 mm or above (for a subject distance of 15 feet).
580ex: светодиоды подсветки автофокуса -
02.08.2005, 16:58
Линейный вид
