How many megapixels can a lens resolve?

Discussion in 'Digital Photography' started by Chris7, Jan 21, 2010.

  1. Chris7 macrumors 6502

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    #1
    In a review of the Nikkor AF-S 24-70mm f/2.8G ED, Photozone said, "At 24mm and 40mm the center resolution is likely to match and possibly even exceed a 10mp sensor resolution and that's also at f/2.8 which is quite amazing."

    This got me wondering, how many megapixels can a decent lens resolve?

    I suppose the answer would be different for full and crop sensor cameras, as 1.5x and 1.6x crop sensors are about half the area of full sensors -- meaning that the pixels on, say a 12 MP crop sensor camera would be about half the size (in area) of those in a 12 MP full sensor camera.

    (BTW, I'm don't want to accidentally start a heated discussion here. I'm sure there reasons why one would want a camera that has more megapixels than lenses can resolve.)
     
  2. mtbdudex macrumors 68000

    mtbdudex

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    #2
    Quick google on "How many megapixels can a lens resolve", these were decent reads:
    http://photocamel.com/forum/photogr...megapixels-will-outresolve-camera-lenses.html

    http://www.pbase.com/tonylong/digital_optical_resoution
    This appears a few years old, still:
    http://www.luminous-landscape.com/tutorials/resolution.shtml

    http://www.impulseadventure.com/photo/megapixels.html

    http://wiki.answers.com/Q/How_many_megapixels_would_it_take_to_equal_a_35mm_film_maximum_quality
     
  3. ChrisA macrumors G4

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    #3
    You can work it out yourself. What size is your sensor? How many pixels? Lets assume a 16x24mm CCD that is 24MP. That would be 6,000 x 4,000 pixels.
    This works out to 6000/24 = 240 pixels per millimetre. A very good but not exotic lens might resolve 100 lines per mm. To sample a line in therory you need two pixels but in real life at least 2.5 pixels. Guess what? A crop-body SLR with 24MP could fully take advantage of a good lens.

    Another way to take advantage of that lens would be to buy a 1970's vintage film body for about $100. And then not only do you get the higher resolution for "full frame" as well.

    A full frame sensor would need 50MP to fully take advantage of the better lenses

    But in real life, lenses don't resolve 100 lines/mm. To get to that level your technique must be perfect using a tripod and the "correct" aperture and selecting only the best lenses. A more realistic number is 50 lines/mm. If you go with this number then you divide the above MP counts by 4. So if a 6MP crop body would be "good enough" and a 12MP ful frame body would be good enough to capture 50 l/mm.

    You can work out other values, the resolving power of the sensor is proportional to the square root of the pixel count. For example for a fixed sensor size a 12MP camera has 1.4 times the resolution of a 6MP camera. and a 24MP camera has twice the resolving power as a 6MP camera. You can easly work out the number of pixels per mm. Multiply by about 2.5 to get the lines/mm figure.
     
  4. VirtualRain macrumors 603

    VirtualRain

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    #4
    So is the moral of this story, that today's sensors have enough pixels and that other factors are now limiting the sharpness of the image?
     
  5. ChrisA macrumors G4

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    #5
    No. There are few 24MP crop bodies and 50MP full frame bodies. But that is what it will take to get quality comparable to the best film

    But for every day snap shots, yes current cameras are good enough.

    People today who need a very high resolution and very low noise are doing the exact same thing they did 50 years ago -- Medium Format.

    Image quality and ultra high resolution have never been the reason to buy a 35mm SLR. People buy them and have been buying them from the late 1950's because they are compact, versatile, fast handling and reasonably affordable.

    Ansel Adam's advice still holds today. He wrote a long time ago "Use the largest camera that will get the shot." And then quickly showed an example photo that he took with a pocket sized range finder camera and explained how he could never have gotten the shot with something larger.
     
  6. splitpea macrumors 6502a

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    #6
    At DPReview they include resolution tests in their reviews of new DSLRS, typically using very good lenses. They include comparisons to other bodies in the review -- and so far it seems that we're still at a point where increased sensor resolution increases the LPI that is resolved. When we get to the point of diminishing returns, it'll be pretty clear from their tests.
     
  7. toxic macrumors 68000

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    #7
    no. there is more to resolution (and image quality) than whether or not the sensor outresolves the lens. The understated utility of smaller pixels.

    caveat for digital: MF backs are designed for use at or near base ISO, so you don't get the "low noise" advantage beyond ~ISO 200.
     
  8. Westside guy macrumors 601

    Westside guy

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    #8
    If you look at lens reviews on the Digital Photography Review site, you'll see they include a line labeled "Nyquist frequency" on the resolution plots. This is the theoretical limit to the sensor's resolving power. You'll notice that it's not common for a lens to hit that mark on a high-res FX body (such as the Nikon D3x), especially wide open.
     
  9. Knomad macrumors newbie

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    #9
    This is a useful generalization. The better full-frame sensors require some pretty good glass to make a match.

    To expand on this: There's always a limiting factor, the only question is what it will be. The very best lenses... Leica, Zeiss, some of the better pro-level ED glass from Nikon or L glass from Canon, will exceed that Nyquist limit even with an FX sensor... at least stopped down and in the center of the image. performance falls off for most lenses wide open or stopped all the way down, and it tends to fall off first in the corners. But if you're willing to spend what it takes to get the best lenses, they usually won't be your limiting factor.

    On the other hand, a cheap kit zoom or off-brand lens will almost always be a limiting factor, that is you'll bump up against the limits of the lens well before reaching the full capability of the sensor, even a DX sensor.

    Also, most DSLRs have anti-aliasing filters which remove moire artifacts but also degrade resolution. Note that most medium format digital cameras, as well as the Leica M8, M9, and S2 do not have anti-aliasing filters so the full resolving power of the sensor and the lenses becomes available.

    However as stated above, most photographers are unable to take full advantage of the capability of their lenses and sensors. Camera vibration, exposure errors, post-production shortfalls, etc., get in the way. Shoot on a tripod, lock up the mirror, nail the exposure, get everything just right in post... then it becomes fair to talk about the limits of resolution.
     
  10. Chris7 thread starter macrumors 6502

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    #10
    Thanks for the info and links, mtbdudex, ChrisA, Virtual Rain, splitpea, toxic, Westside guy, and Knomad. :)

    I’ll look though the links this weekend.

    -Chris
     
  11. Westside guy macrumors 601

    Westside guy

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    #11
    This is such a good point that I had to reply to it, just to get people to read it again. :D
     
  12. Chris7 thread starter macrumors 6502

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    #12
    How many megapixels can a lens resolve at high ISO?

    I looked though the link. Makes sense enough to me to quadruple the number of pixels "needed" to resolve the lens, for reasons listed in this link and by others on this thread (the fact that an optical low pass filter requires that any information touch at least four pixels, for example).

    So I'm wondering,

    How many megapixels can a lens resolve at high ISO?

    (Lets say, the kind of noise one would see at ISO 1600 with a D700 or 5D Mk II.)
     
  13. gnd macrumors 6502a

    gnd

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    #13
    Exactly the same as at low ISO. A lens doesn't know what kind of camera it is mounted on. Could be a 35mm film camera with a roll of ISO 800 film, could be a D700 at ISO 6400 or it could be a APS-C camera at ISO 100. Quality of glass is not a function of available light.
     
  14. thesmall macrumors member

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    #14
    i have also heard about 32 mega pixel... looks pretty amazing...
     
  15. Chris7 thread starter macrumors 6502

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    #15
    (oops. going through so many threads I posted on wrong one)
     

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