пятница, 26 декабря 2008 г.

Lens Angle Underwater

Most popularly used cameras, however, are designed as a land camera with a fixed focal length of 38 mm or 45 mm somewhat on the wide-angle side. Even cameras with a zoom capability are usually designed as a land camera with the field angle (or the light-receiving angle) of the lens selected to cover a portion of the so-called wide-angle region and a portion also of the so-called telephoto region such as the range of 35-70 mm. When such a camera is used in water, it cannot function as a wide-angle camera. In other words, since the index of refraction of water is 1.33 and considerably higher than that of air (=1.00), a lens with a fixed focal length of 35 mm or 45 mm in the above-water condition (or in air) will function in water as a lens with a focal length of 50 mm or 65 mm, and a zoom lens of focal length 35-70 mm in air will function as a zoom lens of focal length about 50-100 mm in water. In either case, the lens will not function as a wide-angle lens.

Here's a table showing typical angle of view for lenses on different camera systems...





Macro photography under water

The secret is to work with a small strobe, placed back sufficiently to still appear large (some need a diffuser), while lighting nearest and furthest point in the focal plane with the least difference. By pointing the light a little too far to the opposing side, one uses the environment as reflector to bring light in the shadows while also lighting less of the near side. Understandably, when shooting at variable distances, this compromise must be rearranged each time, resulting in constant adjustment of the strobe. How easy you can do this, makes a large difference to your chance of success.

Calculating a camera's angle of view

Angular Field of View Calculator

This calculator computes the angular field of view for a lens of a specified focal length on a 35mm camera. For most modern digital SLR cameras (e.g. Canon D60, Canon 10D, Nikon D100, Fuji S2), a focal length multiplier of greater than 1 is appropriate because these cameras have a smaller sensor than a 35mm negative. For these cameras a focal length multiplier of approximately 1.5-1.6 is appropriate. Note: This calculator assumes a standard width/height image ratio of 3:2.

The angle of view of a lens is calculated using the following formula:

2 x tan-1( l / (2 x f) )

where ' l ' is the length of the frame in the direction that you want the reading and ' f ' is the focal length of the lens.


Calculating a camera's angle of view

For lenses projecting rectilinear (non-spatially-distorted) images of distant objects, the effective focal length and the image format dimensions completely define the angle of view. Calculations for lenses producing non-rectilinear images are much more complex and in the end not very useful in most practical applications.

Angle of view may be measured horizontally (from the left to right edge of the frame), vertically (from the top to bottom of the frame), or diagonally (from one corner of the frame to its opposite corner).

For a lens projecting a rectilinear image, the angle of view (α) can be calculated from the chosen dimension (d), and effective focal length (f) as follows:[3]

alpha = 2arctan{d/2f}

d represents the size of the film (or sensor) in the direction measured. For example, for film that is 36 mm wide, d = 36 mm would be used to obtain the horizontal angle of view.

Because this is a trigonometric function, the angle of view does not vary quite linearly with the reciprocal of the focal length. However, except for wide-angle lenses, it is reasonable to approximate

alpha=d/f radians or (180d/pi* f} degrees.

TTL, E-TTL, i-TTL, ...

Compare Strobes by Model

TTL, E-TTL, i-TTL, ...

Digital SLRs do not use the conventional Nikonos TTL protocol, but use their own proprietary version like E-TTL (Canon), D-TTL and i-TTL (Nikon, Fuji). These cameras can generate multiple pre-flashes (sometimes up to 15) as well as a pre-flash with an extended duration. Standard TTL strobes are therefore not capable of working with these cameras. In order to work with these TTL protocols, conversion equipment is required or strobe manufacturers should support them in future models. The Sea&Sea YS-55TTL/E strobe has got Canon E-TTL support and Ikelite is also working on their DS-50 and DS-125 flash systems to support digital TTL protocols (read the Ikelite E-TTL article for more information).

Auto TTL

Some strobes, like the Sea&Sea YS-90Auto for example, offer a special slave mode that claims to automatically adjust the power output to the conditions. This method is based on setting the camera's aperture on the strobe, and the strobe matching its output by measuring the ambient light with its own meter.

This mode may not always be usable given the fact that not all compact cameras show the aperture to the user (nor allow manually setting it). Furthermore, the position of the strobe may cause it to measure area with different brightness than the camera is looking at, and thus still producte over or underexposed photos.

S-TTL / DS-TTL

Strobes such as the Sea&Sea YS-110 TTL and the Inon D-2000 offer these optical slave-TTL types. With S-TTL (Optical Syncro TTL) and DS-TTL (Digital Slave TTL) the external strobe not only watches the start of the camera's internal flash, but also when it stops. When the camera has determined the proper amount of light for correct exposure has been received, it will stops its strobe and therby also the external strobe indirectly.

четверг, 25 декабря 2008 г.

Patima Canon 450D housing

The Patima Canon 450D housing retails for $1500 and is a basic housing that supports the Canon EF-S 60mm macro lens and 18-35 lens. There is no zoom/focus knob on the housing itself, but the port features a zoom gear. Two Nik5 bulkheads and two optical fiber bulkheads come standard, but users can also choose a 6-pin Sea & Sea type bulkhead. Ergonomics are weak on the Patima; similar to Ikelite housings and older Aquatica housings, housing knobs are not accessible from shooting position. Still, it is a nicely made housing, and the price is right.


PATIMA PDCH 450D Gehäuse Kit
1,890.00 EUR


Patima Housing for Canon 450D XSi
Reef Photo Price:$1,500.00

boot 07 Reportage Foto News

DS-TTL underwater strobe

The YS-110 strobe... When it's connected via a fiber-optic cable to a compact digital camera with TTL metering, the YS-110 strobe offers DS-TTL (Digital Slave Through-The-Lens) light adjustment. DS-TTL follows the camera's TTL-adjusted flash for automatically accurate flash photography.

суббота, 20 декабря 2008 г.

CMOS versus CCD

Информация о снимке, которая может быть "записана" на 35мм слайды или негативы соответствует приблизительно 30Мб - по отношению к цифровой обработке изображений с глубиной цвета 24 бита (16.7 миллионов цветов). Обрабатывать слайды или негативы можно слайд- или фильмсканерами высокого качества с разрешением приблизительно 2700 dpi. Изображения, полученные таким путем с разрешением 3,855 x 2,570 пикселей могут быть распечатаны на бумаге без значимой потери качества размером до стандарта А4. При больших форматах качество теряется и при близком рассмотрении изображение выглядит размытым.

Следующая таблица показывает разрешения цифровой камеры и максимально возможные размеры печати при разрешении 300 dpi.

Для сравнения: физические разрешения Fujifilm Frontier Digital Minilab - 1,052 x 1,501 - 9 x 13 cm, 1,206 x 1,796 - 10 x 15 cm, 1,501 x 2,175 - 13 x 18 cm, 2,399 x 3,604 - 20 x 30 cm.


Сравнение матриц зеркальных и компактных цифровых фотоаппаратов

Матрица

CMOS versus CCD

CCD vs. CMOS

Цифровые камеры: цифрокомпакт VS зеркалка

четверг, 4 декабря 2008 г.

Бытие и сознанме, что первично?

Sprich, die Erwartung bewirkt den Eintritt der Erwartung. Das ist eben auch bei der Deflation so und einer der Gründe, warum eine Deflation, die sich einmal etabliert hat, so schwer zu bekämpfen ist.
Jochen Steffens

Мистика и реальность
Ожидание события в массовом сознании порождает ожидаемое событие.

Мистика или реальность?

Это пример влияния массового (планетарного) сознания на реальность. Так что же тогда первично? Бытие или сознание?