Rating lenses

Discussion in 'Photographic Discussions' started by Actor, Nov 5, 2009.

  1. Actor

    Actor TPF Noob!

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    Is there some kind of metric for rating lenses? I.e., some kind of number, or set of numbers, that one could point to and say "this lens is better than that lens?" Like how sharp it can focus, or how bad its chromatic aberration is?
     
  2. KmH

    KmH Helping photographers learn to fish Supporting Member

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    Yes, there are several ways:
    • Surface profile measurement using both contact and non-contact profilometers
    • Surface surveying using methods developed by Foucault and Ronchi
    • and Interferometric testing.
    Most photographic lenses that are tested independently are studio tested and results like these can be found online. Hover your cursor over the image and move it sideways. You can also change the aperture.

    Not all lenses get tested in this manner.
     
  3. Derrel

    Derrel Mr. Rain Cloud

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    The MTF graph is a universally accepted method within the lens making industry of representing optical performance. There are a number of on-line article that attempt to help people to understand how to look at an MTF graph and put the information into context.

    This article is a pretty good explanatory text. Modulation Transfer Function (MTF)

    Other methods involve measuring line pairs resolved per millimeter, or the newer Line Widths Per Picture Height system; these results are usually measured and either shown in chart form, or in graphical form. Chromatic aberration can be either lateral--easily corrected in software, or longitudinal or "bokeh CA", which is very difficult to remove.

    The web site photozone.de does a reasonably good job of measuring CA in pixel units at center and edge,and also uses the LW/PH numbers in bar graph form. It's tough to reduce a lens *only* to numerical values,since they do not describe all the properties of a lens, like how it "draws", just as one example. Lenses also perform differently at different distances; many macro lenses do rather poorly at normal lens testing distances but are superb peformers at focusing distances so close that regular lens testing charts and procedures are not applicable,and some wide angle lenses have rather extreme field curvature issues which might make their pictures look very interesting on real-world, 3-D scenes, but which due to field curvature will not test well on a flat lens test target. Some lenses, like the Nikkor 135mm f/2 Ai-S for example, are rather poor at close range, and look poor at portrait ranges, but when the focus distance is close to Infinity, become stellar performers.

    In short, the MTF graph is the best 'indicator' or 'descriptor' , but a verbal description and verbal summary will,many times, bring insight into how a lens performs in certain situations. Resistance to ghosting and flaring for example--MTF graphs are not a substitute for walking outside and pointing the lens at a blazing summer sun and shooting some frames. Or, as KmH is probably familiar with, pointing a lens toward brilliant stadium lights at night, with a large expanse of black field aka "sky".
     
  4. Plato

    Plato TPF Noob!

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    Look for the letters "N i k o n"

    :lol:
     
  5. Actor

    Actor TPF Noob!

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    Never heard that one. I have been told to look for the letters "Z e i s s." :lmao::lmao:
     
  6. PatrickHMS

    PatrickHMS TPF Noob!

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    What is that other name of a lens mfg, something like Zeiss Nikon ?

    lol
     
  7. Garbz

    Garbz No longer a newbie, moving up!

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    Unfortunately lots of the measurements are very one sided, and don't show the full story.
    e.g. the worst lens I have used, the Nikkor 18-200 f/3.5-5.6 measures awesomely in sharpness and CA at 50mm. Doesn't change the fact it's a pain to use because of lens creep and all around hard to manufacture design.

    e.g. the Nikkor AF 80-200 f/2.8 D is an awesome lens in all measurements, however at it's nearest focus distance at f/2.8 zoomed to 200mm it is horrid. This doesn't show up on graphs because a lens like that is rarely measured at near focus distance.

    So yes there are metrics to measure lenses, but you're unlikely to find a full complete set for given lenses that explain how it performs in a wide variety of conditions.
     

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