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Beyond Megapixels - Part II

Posted by michael on from the point-and-shoot dept.

TheTechLounge writes "This is Part II of a series of three editorial articles examining current digital photography hardware, as well as my views of what is to come. In this segment I will be focusing on build, size, weight and ergonomics of camera bodies, as well as the size, weight, function and versatility of the glass strapped to the front of it. If you haven't already, you may want to read Part I first."

8 of 135 comments (clear)

  1. Article is Wrong on Lenses by hanway · · Score: 5, Informative
    The article started out okay, although taking a whole page to say little more than "DSLRs are big", but on the second page I came to this statement as a justification for using smaller lenses in DSLRs:

    The sensor only receives the light that passes through the center of the lens, while the light on the outer region simply falls to the side of the sensor.

    That's fundamentally wrong. A light ray that falls on any part of the lens can be refracted to any point on the focal plane. What gets focused onto the sensor in the center of the focal plane is not just the light that passed through the center of the lens, but part of the light passing through the entire lens.

    The author is right that a range of smaller lenses would help reduce camera size, but with a smaller lens comes less light gathering ability and reduced ability to take advantage of depth of field when composing a photo, so smaller lenses would be a compromise in photo quality.

    1. Re:Article is Wrong on Lenses by dfghjk · · Score: 5, Informative

      The author also missed the point that DSLR's are an attempt to make cameras that best utilize existing lenses. He says over and over that the lenses aren't necessary for the camera but that's meaningless. The lenses come first and the bodies follow. This is the best they can do at the price point and time.

      He also stated that the 2/3" lens and DLSR lens at f/2.8 have the same light gathering ability. That's wrong. They have the same exposing rate ability but the SLR lens has greater light gathering ability because it exposes a larger image circle.

      Frankly, everyone should ignore these articles. The author doesn't know enough about the subject to do anything but damage.

    2. Re:Article is Wrong on Lenses by kfg · · Score: 5, Informative

      The author also missed the point that DSLR's are an attempt to make cameras that best utilize existing lenses.

      ". . . by utilizing the interchangeability of the lenses on a DSLR, you open yourself up to the use of dozens of lenses appropriate for all kinds of various uses and prices from around $60 up to, and in excess of, $8,000. For photographers switching from a film SLR to a DSLR of the same brand and mount, this means your investment in lenses does not go out the window."

      KFG

    3. Re:Article is Wrong on Lenses by dfghjk · · Score: 5, Informative

      f/2.8 would be a specific rate of exposure per unit of imager area. It would expose at the same rate regardless of the size of the imager. The sensitivity of the imager is rated by ISO and is also a rating per unit area. In this way, cameras with identical ISO ratings and f-stops will require the same shutter speed regardless of imager size. That how you want it to work.

      Light gathering ability of the lens, however, is not per unit area. It means the total ability to gather light. Therefore a lens that covers a wider area at the same f-stop will have greater light gathering ability than its competitor. Whether that larger image circle is actually used is beside the point. The author was incorrect stating that the two lenses have identical light gathering ability. He would have been right had he said "exposure ability".

      Two cameras with different sensor size but identical ISO's and f-stops will require the same shutter speed for proper exposure, but the camera with the larger sensor requires more light to expose due to its larger imager area. Where does this extra light come from? Not from increased exposure time since the shutter speed is the same. It comes from the lens delivering more total light. This occurs because its lens actually has a larger physical aperture to achieve the same f-stop and the larger aperture allows more light through the lens. The "luminous flux" is unchanged, however, because it's spread over a larger area. How does the lens get away with this? The larger sensor area requires a longer focal length lens for equivalent perspective and f-stop = (focal length/physical aperture). It's all cleverly hidden in the math. Perhaps a little too cleverly.

  2. Telecentric Lenses and Silicon by G4from128k · · Score: 5, Informative

    The article mentions the excessively large size of 35 mm lens for imaging on to small digital sensors, but misses the two additional problems with using film camera lenses with digital sensors.

    Standard film camera lens tend to transmit light from the subject to the sensor at the angle that it was received (similar to the way that a pinhole camera projects a bundle of rays from object space to image space). Silicon sensors suffer from two problems when light enters them at an angle. First, the high index of the material and coatings tends to reflect the angled light -- causing less light to enter the sensor and the image to have dark corners. Second, long wavelength light penetrates the sensor deeper than does short wavelength light. If the light enters at an angle, the red photons can angle down into the substrate and actualy register in pixels further out. The result is that the red and infrared portions of the image are misregistered, causing color fringing in the corners.

    The point is that the best lens for a digital camera will be different from the best lens for a film camera. A better lens design for digital cameras incorporates image-space telecentricity. Image-space telecentricity means that the light hitting the CCD is largely perpendicular to the sensor.

    --
    Two wrongs don't make a right, but three lefts do.
    1. Re:Telecentric Lenses and Silicon by jdg · · Score: 5, Informative

      I design lenses for a living.

      This statement is sort of correct. The real need for telecentricity is the limited acceptance angle of the lenslet arrays that are put on many sensors, particularly small pixel size consumer grade sensors. This is what causes the drop off in corner illumination with non-telecentric lenses in consumer grade digital cameras. Telecentricity is a real requirement, particularly in sensors which pixel sizes smaller than say 4um.

      Large pixel, higher end CCDs generally don't need the lenslet arrays because the fill factor on the pixel aperture is much larger, so there is not much of a problem with non-telecentric designs. There are no lenslets present to limit the acceptance angle. I have never seen reflections off the sensor be an actual problem. People also talk about ray bundles from one obliquity passing through the wrong filter on the color filter array in a non-telecentric design, but I have never seen this happen either.

      Longer wavelength light is generally eliminated by an infrared reject filter, so light rarely bleeds from pixel to pixel.

  3. Re:35mm by sdr · · Score: 5, Informative
    There are two digital SLR cameras in market right now with full 35mm sensors - the Canon EOS-D1s and the Kodak DCS SLR/n. The Canon is an 11 MP camera and costs about $8000.00. The Kodak is a 14MP camera costing about $5000.00. The Canon produces the best quality pictures among digital SLRs. The Kodak is rather new. It is actually an update of an older camera using the same sensor called DCS 14n. This older model has been described as rather noisy (in comparison to the Canon at least) in all but the lowest ISO setting. It also produced bad colors in certain situations. The new model supposed to be better - but not in the same class as the Canon. The Kodak uses Nikon lenses and is based on a Nikon camera body. Kodak has also announced another body with the same sensors that take Canon lenses.

    So at least two full 35mm frame digital SLRs exist. None of them are cheap - and it it will quite possibly stay that way for some time.

    Leica has announced a digital back for their R series SLR cameras. This being Leica, it will possibly be rather expensive - not to mention the huge price tags for their lenses and film bodies. There has been some persistent rumors that Nikon is designing their next professional flagship SLR camera body (the successor to the film SLR model F5) as a camera that can take interchangable digital (and film) backs. Nikon flagship models are usually replaced every 8 years. If the pattern holds then they should come up with a new model (the F6) this year.

  4. Re:What is this article trying to say? by carlislematthew · · Score: 5, Informative
    It seems that Nikon are avoiding the 35mm size sensor more than anyone else. They've come out with these crippled "digital" (or whatever) lenses specifically for their DSLR range.

    Right now, Canon actually *has* a 35mm sensor DSLR (EOS-1Ds) - it's supposed to be awesome, as well as being awesomely expensive ($9,000ish I believe). From what I've read, the problem is the low yield on making the sensors themselves and also some fancy expensive anti-aliasing filter that goes in front of the sensor.

    Unfortunately, I don't think you can compare yield improvement of expensive 35mm 12MP sensors with yield improvement (and therefore cost reduction) on things like LCD flat panels. The reason is that consumers don't *need* image quality like the Canon EOS-1Ds provides. It's almost medium format quality and 99% of consumers used crappy tiny-lensed 35mm negative film for years, printed by shitty machines on 4x6 paper that fades.

    So if it *is* the case that 35mm sensors are the future for DSLRs, I do not believe we can expect the kind of quick generational reduction in cost that we're used to for other more "commodity" consumer items like LCD flat panels, PDAs, cell phones, and so on.