Popular opinion states that the more megapixels a cameras sensor has then the clearer the resulting image and therefore better quality. Camera manufacturers have for some time been involved in a race to create affordable high resolution image sensors within the bounds of AP-S and 35mm format. This article is concerned only with cameras from manufacturer Nikon and assesses resolution from three models D2Hs, D70 and D2X which have native resolution of 4.1, 6 and 12.4 megapixel sensors. Whilst the author does not hold an exhaustive range of lens charts, images are examined using the same test piece for a real life comparison. All images are assessed on equal terms but due to logistical issues concerned with supplying every reader of this article with a printed 6 x 4 photograph images are presented at monitor resolution - 72 dpi (Dots Per Inch) therefore every reader can view a representation of each photograph suitable to computer monitors.
A megapixel is a one Million picture elements so the understanding that more equates to better images is a logical one. However the truth is often realised when a photographer purchases a new higher pixel count camera and discovers that the images are often worse then their older lesser pixel count camera. When the same AF-S area of approx 24 x 16mm is used the only physical way to arrange more pixels is to employ smaller and smaller photo-sites. This may result in increased noise (unwanted speckles due to non-linear output of each pixel when subject to equal light energy) as a smaller element is not exposed to the same amount of light energy or photons as a larger one therefore electronic amplification is required to increase a pixels output level which is governed by aperture, exposure time and ISO speed. In theory all cameras regardless of manufacturer should output the same brightness for a given ISO, exposure and lens aperture. If noise prone electronic amplification is not used then another way of keeping within these bounds is to reduce the ISO speed rating i.e if the sensor output is low due to an increased pixel count then the output could be rated at different ISO level i.e. 1/125 at f4 produced half the level it should at ISO200 then a manufacturer could claim the sensor output is at ISO100 whereby the photographer can increase ISO speed to increase output. A higher pixel count sensor as well as recording more detail will record more flaws such as lens aberrations and poor technique from the human photographer. If a chromatic aberration exists from a consumer lens used on a 4MPx (MegaPixel) camera then the extent of colour shift maybe across ½ pixel and not recorded but the same lens used on a 12MPx camera could have colour shift across three pixels each side of a high contrast edge resulting in six pixels being exposed to lens aberration which could definitely be recorded. The same applies for poor technique an edge may be blurred across one pixel on a 4Mpx but this may be three with a 12Mpx image to show perfect results viewed on computer monitors at full pixel count from higher resolution sensors perfect technique must be employed.
Camera sensor specifications
D2Hs, 4.1 Million Pixels (2464 x 1632) 23.3 x 15.5mm. JFET LBCAST
D70, 6.01 Million Pixels (3008 x 2000) 23.7 x 15.6mm. CCD
D2X, 12.4 Million Pixels (4288 x 2848) 23.7 x 15.7mm. CMOS
Notice differences in physical size between all cameras and difference in sensor technology as the motivation of this article is image quality between pixel count this will be ignored and has little relevance when images are printed.
Full specifications can be found below
D2H (as only a preview D2Hs) can be found
http://www.dpreview.com/reviews/nikond2h/
D70
http://www.dpreview.com/reviews/nikond70/
D2X
http://www.dpreview.com/reviews/NikonD2X/
The Test
Testing each camera is not about any specific camera, its features or quality instead the test is concerned only with megapixel output so differences in colour, exposure and noise are ALL ignored. It must be reiterated that this test is purely concerned with megapixels.
A teddy bear was selected for fine detail in its synthetic fur and especially a course weave ribbon around its neck. All images recorded using the same 50mm f1.8 lens at f8, reviewed by Bjørn Rørslett (
http://www.naturfotograf.com/index2.html ) 'having no noticeable difference between f4 and f8'. Aperture f8 was chosen at the end of this range to provide maximum depth. A solid slik professional tripod was used to avoid any motion shake and all recorded using Nikon Camera Control Pro (computer tethered) to avoid any human induced vibration.