FIELD IN FO CUS

THERE IS NOTH­ING WRONG IF PARTS OF YOUR PICTURE ARE BLURRY. IN FACT, CREATIVE USE OF DEPTH OF FIELD CAN GIVE AN AURA OF MYS­TERY TO THE PICTURE.

Gadgets and Gizmos (India) - - DIGITAL LIFE - TEXT & PHO­TO­GRAPH BY RA­JWANT RAWAT

When you take a pho­to­graph, the ob­jects ly­ing within the fo­cal length of the lens is sharper in con­trast to those ei­ther fur­ther away from the lens or closer to the cam­era. The range be­tween the sharpest near­est and far­thest points is called “depth of field”. You can cre­atively use depth of field in pho­tog­ra­phy. Knowl­edge of depth of field can make your pic­tures in­ter­est­ing. For in­stance, by putting your sub­ject in sharp fo­cus, while si­mul­ta­ne­ously en­sur­ing the back­ground is out of fo­cus, you will cre­ate a picture whose sub­ject is not clut­tered by the back­ground.

Fo­cus plays a sig­nif­i­cant part in how good a picture is. By us­ing depth of field, you can play around with the ar­eas in a pho­to­graph that you want to draw at­ten­tion to. With creative use of de­fo­cus, you can add an aura of mys­tery to a picture (much like in a soft-fo­cus pho­to­graph) or cap­ture a glo­ri­ous land­scape with­out parts of it be­ing blurry.

The magic of how to con­trol depth of field lies in your abil­ity to use the aper­ture of the cam­era. The sim­ple rule is that open­ing up the aper­ture de­creases the depth of field, mak­ing it smaller pro­duces the op­po­site ef­fect. A smaller aper­ture, say f11, will give you sharp­ness over a greater area

of the picture than say f4 over the same fo­cal length.

Depth of field can also be in­creased or de­creased by us­ing dif­fer­ent fo­cal lengths. Depth of field in­creases when we use wide-an­gle lenses and it de­creases when we use longer fo­cal length lenses, a 200mm lens for ex­am­ple.

How­ever, re­mem­ber that it isn’t sim­ply a mat­ter of in­creas­ing or de­creas­ing the aper­ture. Sim­ply chang­ing the f num­ber can give you over or un­der ex­posed pho­tos. The aper­ture and the shut­ter speed have an in­verse re­la­tion­ship in con­tin­u­ous light, that is, the big­ger the aper­ture, the faster should be the shut­ter speed and vice-versa. Sup­pose you have set your cor­rect ex­po­sure for a shot to f16 aper­ture and 1/125 shut­ter speed. You then re­alise that you need to step down the aper­ture to f2.8 be­cause you want only the sub­ject in fo­cus. This means that you will open up the aper­ture by five full stops from f16 (11-8-5.6-4-2.8). For the ex­po­sure to re­main cor­rect, you will cor­re­spond­ingly have to in­crease the shut­ter speed by five full stops from 1/125: 1/250-1/5001/1000-1/2000-1/4000. At an aper­ture of f2.8 you will re­quire a shut­ter speed of 1/4000 to main­tain the orig­i­nal ex­po­sure.

When us­ing flash, you will have to con­trol the ex­po­sure by in­creas­ing or de­creas­ing the light in­ten­sity or mov­ing the light source away or closer to the ob­ject.

The top photo has been taken with a 200 mm lens. Com­pare it to the larger range of the 24 mm be­low

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