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Actual prime focal lengths versus manufacturers nominal labeling

Discussion in 'This or That? (MFT only)' started by pigiron, Jul 11, 2018.

  1. pigiron

    pigiron Mu-43 Veteran Subscribing Member

    Feb 27, 2016
    It is well known that lens manufacturers will often describe their prime lenses as say, 50mm when in reality it is actually rounded to that from 48.7, 50.8, or some such This throws off the actual versus calculated angle of view. Other than carefully measuring it oneself do any of the lens review sites publish the actual angle of view rather than just printing what it ought to be according to whats printed on the lens body?
  2. tino84

    tino84 Mu-43 Veteran

    Dec 29, 2013
    It would be easier to check manufacturers’ site, sure in the datasheet you can find the exact angle of view
    • Agree Agree x 1
  3. Carbonman

    Carbonman Mu-43 Hall of Famer Subscribing Member

    Jul 10, 2014
    Vancouver BC
    Focal length can vary with the distance you've focused to from focus breathing. Some lenses have extreme cases. A lot of macro lenses apparently have this issue when focused really close.
    • Agree Agree x 1
    • Informative Informative x 1
  4. The Panasonic 35-100 f/2.8, a bit like the old Nikon 70-200 f/2.8, focus breathes a lot such that at close portrait distances it's more like a 75mm.
    • Informative Informative x 1
  5. Petrochemist

    Petrochemist Mu-43 All-Pro

    Mar 21, 2013
    N Essex, UK
    I take it that's when set at 100mm :hiding:
  6. Yes. And obviously for the Nikon it's referring to the equivalent 200mm setting.
  7. wimg

    wimg Mu-43 Top Veteran

    Dec 10, 2016
    That's true for IF designs, effectively, a form of zoom really.

    Any old school macro lenses do not have this problem. I did some measurements in this regard with my Canon macro lenses (when I had them). The EFS 60 becomes a 50 mm at 1:1, and the EF 100 mm, both the non-L and the L, become a 70 mm at 1:1. The 180L, which I still own, becomes a 120 mm at 1:1 if I am not entirely mistaken. The latter I would have to check again, can't remember the exact details.

    Basically, this is a general problem with IF lenses. although Canon's L-zooms are all quite stable in this regard, as far as I am aware, certainly the 70-200s, and the 100-400s. Nikon has always been a problem in this regard, but generally the worst are the long range zooms from 3rd party manufacturers.

    Kind regards, Wim
    • Informative Informative x 1
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