Pixel density, noise & megapix­els

NPhoto - - Feature -

Megapix­els are not the only fac­tor in im­age qual­ity; the size of the pix­els (or ‘pho­to­sites’) also mat­ters. Big­ger pho­to­sites mean less noise and bet­ter dy­namic range; smaller pho­to­sites mean more noise and less dy­namic range. So be­cause the DX-for­mat sen­sor in the D500 is smaller, there’s a limit to how many megapix­els Nikon can cram in be­fore these other as­pects of im­age qual­ity start to suf­fer. Nikon has used 24-megapixel DX sen­sors, but it clearly feels 20 megapix­els gives the ideal com­bi­na­tion of res­o­lu­tion and over­all im­age qual­ity in the D500. In prin­ci­ple, the smaller pho­to­sites in the D500 should put it at a dis­ad­van­tage at high ISOs. But it’s a newer-gen­er­a­tion sen­sor than the D750’s and its max­i­mum stan­dard ISO is ac­tu­ally higher (51,200 ver­sus 12,800), giv­ing greater flexibility if you’re shoot­ing in the dark or if you need ac­tion-stop­ping shut­ter speeds. Even so, it’s not nec­es­sar­ily bet­ter qual­ity at the same ISOs as the D750.

The larger pho­to­sites on the D750’s sen­sor should give it a the­o­ret­i­cal noise and dy­namic range ad­van­tage, though the newer tech­nol­ogy in the D500’s sen­sor will off­set this – broadly, though, the old rule ap­plies to sen­sors just as it did to film for­mats: “a good big ’un will al­ways beat a good lit­tle ’un”. The larger sen­sor area of the FX-for­mat D750 means that al­though it has only slightly more res­o­lu­tion than the D500 (24 megapix­els ver­sus 20.9 megapix­els), there’s space on the sen­sor for much larger pho­to­sites and hence the po­ten­tial for lower noise and bet­ter dy­namic range. Al­ter­na­tively, the larger sen­sor area can be used to of­fer much higher res­o­lu­tion with the same pho­to­site sizes – so you get sharper pho­tos with no penalty in noise or dy­namic range. The D810 is a good ex­am­ple of an FX­for­mat Nikon that ex­ploits the

full-frame res­o­lu­tion ad­van­tage.

There’s an old say­ing about film: “A good big ’un will al­ways beat a good lit­tle ’un”, and it’s just as true when comparing dif­fer­ent-sized sen­sors

Newspapers in English

Newspapers from Australia

© PressReader. All rights reserved.