 In other words, there is under normal circumstances a reciprocal proportion between aperture area and shutter speed for a given photographic result, with a wider aperture requiring a faster shutter speed for the same effect.For example, an EV of 10 may be achieved with an aperture (f-number) of 2.8 and a shutter speed of 1/125 s. The same exposure is achieved by doubling the aperture area to 2 and halving the exposure time to 1/250 s, or by halving the aperture area to 4 and doubling the exposure time to 1/60 s; in each case the response of the film is expected to be the same.For most photographic materials, reciprocity is valid with good accuracy over a range of values of exposure duration, but becomes increasingly inaccurate as this range is departed from