Gadgets and Gizmos (India) - - BRIGHTNESS& CONTRAST -

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.

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