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  1. #1
    Junior Member
    Join Date
    Jun 2004
    Dallas, TX, USA

    Bang for the Buck


    Have a look at this MS-Excel spreadsheet:

    The 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 rating, if you will). Obviously, there are many other factors one should consider when choosing a camera system, so please don't beat me up for failing to take everything into account.

    The spreadsheet does make it obvious that sensor size has a dramatic impact on image quality. 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 a 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.

    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

  2. #2
    has-been... another view's Avatar
    Join Date
    Jan 2003
    Rockford, IL
    Whoa... Somebody who made this chart has a lot of free time! They should be out shooting! Like I've got a lot of room to talk, I'm stuck at a desk on this beautiful afternoon.

    I think it's unrealistic and almost meaningless to compare the performance of a camera based just on numbers like this. First off, what lens were the DSLR's tested with? The kit lens? That might discount an otherwise excellent "rating". A lot of DSLR buyers are going to have a bag full of either brand of glass already, so putting a 50mm prime or other very sharp lens will change everything. Does everyone print at 300dpi? I don't. 240 looks good and so do some of the big 180dpi prints I saw made from a 4mp camera. Quality of post processing isn't taken into account either, and this can give you huge variations.

    I don't understand your point about faster lenses, either. Really - not trying to be a jerk or anything - I don't understand what you're saying. From practical experience, only the best lenses are great wide open. Most lenses, even some so-called pro grade lenses, will benefit from stopping down one or two stops from wide open.

    Also, in the final print, there's the "human factor". In my opinion, if you have a shot with very little depth of field, the in-focus area can appear very sharp - maybe even sharper than it actually is. Hard to explain this - you really need to see a print to understand what I mean.

    I just read something that basically sums up my opinion on all this. I wish I had the exact quote with me, but in this month's Photo Techniques magazine, David Vestal says something like "One photograph that conveys emotion beats hundreds of technical masterpieces". His exact quote is much better, but the point is the same.

  3. #3
    Captain of the Ship Photo-John's Avatar
    Join Date
    Aug 2001
    Salt Lake City, Utah, United States

    Good stuff

    The abridged version - bigger pixels are better.

    It's not fair comparing any digital SLR to any compact digital camera. Until the pixel sizes are comparable, digital SLR image quality will crush ay compact digital camera.

    There's a ton of detail in your post. My eyes started glaze over a little.

    And I confess I didn't look at the spreadsheet. But I will. Even though it's hard to digest, I think this is a great post. And I'm very happy you shared it with us.

    What else you got?!

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