Explain DxO lens ratings

Discussion in 'Open Discussion' started by MacBook, Feb 23, 2014.

  1. MacBook

    MacBook Mu-43 Veteran Subscribing Member

    Jul 24, 2010
    South Carolina
    I remain flummoxed at the lens charts on DxO. I think I understand them, but am not sure. Could someone with expertise confirm that I am reading these correctly, or explain?

    Screen Shot 2014-02-23 at 10.12.27 AM.

    Sharpness -- the higher the number, the longer the bar, the more sharpness

    Transmission -- the smaller the number, the longer the bar, the more light transmission? It says, "T-stop has the same meaning as the lens f-stop and utilizes similar values. Smaller numbers mean more light. "

    Distortion -- the smaller the number, the shorter the bar, the less distortion

    Vignetting -- the smaller the number, the shorter the bar, the less vignetting

    Chromatic aberration -- the smaller the number, the shorter the bar, the less chromatic aberration
  2. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Sean Rastsmith
    T-stop is the actual amount of light reaching the sensor (useful for video in switching lenses, and ensuring exact exposure match). Fstop is a ratio of physical aperture dimension vs focal length. Tstops will always be higher than f-stop (t=f means 100% light transmission~impossible). So leaving off the last lens (as it is a variable aperture, and not sure where it is measured), the 35-100 has better transmission vs the Olympus by a bit. IIRC, T-stops also follow the sqrt(2) progression like aperture (1,1.4,2,2,8,etc) so .1 difference isnt linear (3.3~3.4 is a larger difference than 9.3~9.4). Otherwise, I think you are correct.
  3. pdk42

    pdk42 One of the "Eh?" team

    Jan 11, 2013
    Leamington Spa, UK
    The DxO lens ratings are notoriously controversial and hard to interpret. The overall figure is a melange of the other scores and since this includes the aperture/T-stop, then anything other than bright lenses get marked down. This is odd IMHO since we all know what we're getting into aperture-wise with a particular lens - what we want to know are its other qualities! Of the other measures, the sharpness one is odd since it's called "Perceptual Mega Pixels" and is some odd synthesis of sensor and lens resolving power. Since u43 cameras have lower pixel counts, then all u43 lenses get rated lower than FF lenses - which also rather odd.

    Personally, I'd go elsewhere for lens tests - the DxO ones are too flawed/over-complicated for my taste.