Bang for the Buck

Discussion in 'Digital Photography' started by Michael K. Davis, Jun 18, 2004.

  1. Hi!

    Have a look at this MS-Excel spreadsheet:

    This spreadsheet attempts to grade several digicams and DSLRs in terms of their print sizes at 300 dpi, Depth of Field available at the aperture where diffraction would prevent us from achieving a print resolution of 5 lp/mm (the equivalent of 300 dpi), and the number of available stops that are larger than that camera's aperture at which diffraction prevents 5 lp/mm. A composite score that's independent of street price is calculated, as well as a composite score vs. street price (a bang-for-the-buck ratin
    g, if you will).

    For example, the Nikon Coolpix 8700 has a 300 dpi print width of 10.88 inches - just a wee bit larger (more desirable) than the Canon EOS 300D's 300 dpi print width of 10.24 inches. But the Coolpix 8700 can not actually achieve 5 lp/mm in its 300 dpi print if it stops down below f/4.7, thanks to diffraction's Airy disks reaching a diameter greater than 0.2 mm in the final print (the reciprocal of 5 lp/mm).

    But the Canon EOS 300D, thanks to its larger, lower density sensor, can deliver 5 lp/mm at any aperture wider than or equal to that had at f/12.9.

    So, to maintain 5 lp/mm resolution in a 10.5 inch print, the Coolpix 8700 user must avoid stopping down below f/4.7, but the EOS 300D user can go all the way to f/12.9.

    The maximum aperture will vary from lens to lens with DSLRs, but hey, there's a huge difference between a camera that can deliver 5 lp/mm resolution to a ten and half inch print with only a couple of stops to play with, versus one that allows you the freedom of several stops.

    Let me know when the digicams with pixel densities in excess of 300 pixels per inch are equipped with superfast lenses. To enjoy the range of available diffraction-free stops (4 and 1/3 stops) offered by an f/2.8 lens mounted on the Canon EOS 300D, the Nikon Coolpix 8700 sensor would have to be companioned to an f/1.0 lens. To match the available stops of an EOS 300D's f/1.4 lens, the Coolpix 8700 would have to open up to f/0.5 lens.

    How much higher can they raise the pixel densities without giving us faster lenses too? Answer: They can keep raising the densities until the majority of buyers realize their images are being degraded by diffraction.

    I don't want faster lenses for tiny, high-density sensors. There's a limit to how much resolution can be delivered at even f/1.0. Incorporating variable neutral density filters to provide additional diffraction-free "stops" isn't the solution either. I want bigger, lower density sensors, made more affordable by mass production.

    Mike Davis

    Michael K. Davis, Jun 18, 2004
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