PHOTOGRAPHY -23

 PHOTOGRAPHY -23

Technical features to understand

EXPOSURE – The act of permitting light-impingement on to a film; it has a set of controls to abide by. These are a] Shutter speed and b] the value of Aperture or Diaphragm as known in literature.  The shutter is an operable device in a camera by choosing the correct speed and setting the speed dial at that value. Cameras from 1955 and later are equipped with a range of speed settings providing for excellent permutations –in consonance with Diaphragm settings. Shutter speed values read B, 1, 2, 4, 6 ,16, 25, 60, 125, 250, 500, 1000, 2000 and in one case 3000. What do these numbers mean ? Every number is a fraction of ONE SECOND, like 1 = 1/1, 2=½, 4= ¼  etc up to 1/3000 of a second.  B = step for Bulb exposure which keeps the shutter ‘open’ until the trigger is released. Many persons wrongly refer to B as a reference for Brief exposure             [ conceptually wrong]. Obviously, the largest number on speed dial signifies the fastest speed [so, the least exposure]. When would such a speed be of practical value ?

Such speeds can freeze the action of a moving object like a car or a person looping over the bar by pole vaulting  or a player leaping over to thrust the ball into basket or similar such action-packed moments.  While such speeds freeze movement and make the object standstill, such a rapid speed may not provide for the right quantum of exposure; So, a compensatory option is to allow more light to reach the film by opening up the aperture [ or a lowerr diaphragm value like f 5.6  or bigger like f4 or f2 and so on]. In other words  Exposure is a product of the equation E= I X T OR E= I x t where E= Exposure, I or I = intensity [of light reaching the film regulated by Aperture ] and T or t stands for time duration for which, light acts on film [ regulated by Shutter speed]. The Aperture settings or Diaphragm values read f 22, 16, 11, 8, 5.6 , 4, 3.5, 2.8, 2.4, 1.8, 1. 7 and so on. The lower values around 1 or 2.4 vary among different Lens manufaturers to confine the setting  to ensure maximum opening by availing of the total surface of the lens. Invariably,  the lowest setting coresponds the lens power such as 2.8 or 1.8 or 1. 4 as the case may be.

OF WHAT SANCTITY ARE THE NUMBERS ON DIAPHRAGM SCALE?

The numbers on the Diaphragm ring are named ‘f’ numbers: of which the lowest number corresponds to the power of the lens. The relationship between f number and the aperture can be explained thus: The focal length of a lens in mm divided by the diameter of the lens aperture [through whicha light ray is transmitted in] is the  f number.

Eg; A lens of focal length 50mm, set at f4 permits light entry through an opening of diameter 12.5 mm because 50/ 4 = 12.5 0r 50mm focal length lens’ surface of which an aperture of diameter 12.5 mm is used = f4 . For the same lens, an f setting 5.6 means the aperture used = 8.9 mm in diameter and at f 22  , aperture employed uses 2.27 diameter. As the f value increases, the diameter of the availed area is lowered or at lower f values the aperture opening has higher diameter. Narrow aprtures help sharper focus of image and broader apertures permit wider light beam and so  shallow in focus.

Despite the  basic focussing, a diaphragm setting chosen can enhance or decrease depth by the size of the light beam it permits to pass in .

Normally an f stop delivers light -either doule or half in intensity as its neighbour. The same ability is ascribed to a shutter speed in relation to its neighbour except in the case of B. Kindly remember  the values of  f series and those of Shutter speeds.

Some Common functional guidelines in Selection of exposure  for beginners.                                              For bright day light

1 Note the Film speed in ASA [ MORE EASY TO ADOPT]

2 Set the Shutter speed –closest to the FILM SPEED  Eg: For 100 ASA Film select Shutter speed 125. For 64 ASA Sh.speed 60 , For 200 ASA,Sh. Speed 250 etc.

3 Select Aperture  f 11   , Focus  and  Shoot  If in doubt do bracketing with one f stop + and one stop – on f 11  At least one exposure  would be close to the most desirable.

Of course While working with Flash, utilize the GN Value for Aperture  and the best  Shutter speed [for flash] is generally colour-coded by Camera manufacturer  as the shutter should open when flash light is in peak intensity . This co-ordination is called Synchronisation. Improper shutter speds for Flash make incomplete registration of images. 

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