Diffrac­tion

NPhoto - - FEATURE -

The aper­ture your lens is set to con­trols how much light hits your sen­sor for the du­ra­tion of the shut­ter speed and has an ef­fect on the depth of field, but there’s also an­other way it af­fects the im­age – diffrac­tion. Light is scat­tered as it passes close to the aper­ture blades, so the nar­rower the aper­ture the greater this ef­fect – the re­sult is a soft­en­ing of im­age de­tail. So it’s sug­gested you avoid very nar­row aper­tures. The smaller the size of an im­age sen­sor, the more ob­vi­ous the ef­fect. With a large full-frame sen­sor, diffrac­tion be­comes enough of an is­sue for im­age qual­ity to lessen be­yond around f/16, while on a DX sen­sor it’s about f/11.

But it’s not all bad. The scat­ter­ing turns points of light into an at­trac­tive star­burst in night pho­tog­ra­phy, and the soft­en­ing ef­fect is less no­tice­able in dark scenes.

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