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Thread: Focus breathing worse on 100-400 II?

  1. #1

    Default Focus breathing worse on 100-400 II?

    Reading a review of the new 100-400 II a comparison shot showed that the new lens gave a slightly smaller image than the original when focussed at some distance (I don't have the information but would not have been at infinity).
    I compared the image magnification between a 100-400 I and II using two sheets of A4 paper pinned to a tree folded to be 580mm tall (this should just fit an APS-C sensor at 10m). The mk II was indeed slightly smaller than the mk I giving effective focal lengths of 360mm and 370mm respectively. Being rather less than the 400m stated on the tin, I compared moon shots. With a 2xIII extender on both, they were a lot closer. The diameter of the moon measured 7.08mm (assuming that the sensor height was 14.9mm) with the Mk I and 6.98mm on the Mk II. NASA data showed that the moon diameter covered 1837 arc seconds at the time the image was taken. So assuming that the lens effective length is 800mm, the image size should have been 800mm x 1837/3600 and adjusted for radians gave me 7.12mm, making both lenses appear very close to 400mm, with the Mk II being 392mm on that basis. But focus breathing seems to be slightly worse.

    Anyone else noticed?

  2. #2
    Join Date
    Dec 2015

    Default Re: Focus breathing worse on 100-400 II?

    Don't have these, but have you compared the EXIF data? I notice that when I use the Sigma 150 - 600 @600 mm, the data shows a shorter focal length, about 580 mm as I remember. It would be interesting to hear if your calculations and the EXIF data agree.
    Effective focal length does depend on object distance I think?? It's particularly noticeable on macro.
    EOS 6D, 80D, 70D, 100D, 50D. Canon 10-18, 18 - 55, 55 - 250 IS STM lenses, Canon 50 mm F1.8, 60 mm macro, MPE-65 macro, 85 mm F1.8, 200 mm F2.8 L II, Sigma 24 - 35 F2 Art, 17 - 50 F2.8, 105 mm DG OS macro, 150 - 600 C, Kenko 1.4x TC

  3. #3

    Default Re: Focus breathing worse on 100-400 II?

    Both lenses were flat out at 400mm which the EXIF data confirms.

  4. #4

    Default Re: Focus breathing worse on 100-400 II?

    BTW it's image size that depends on distance to the object (for a given focal length).

  5. #5
    Join Date
    Oct 2016
    South Wales

    Default Re: Focus breathing worse on 100-400 II?

    Any lens with multiple elements is a compromise. While these differences my be slightly annoying , surely the most important criteria with a lens is its optical performance with regard to sharpness, aberrations etc. yes I am aware of the phenomena but I really see it as unimportant in the overall scheme of things.
    If it really bothers you, don't buy the lens, although I suspect that other lenses will also have problems.
    5DMk IV, 5D Mk III, EOS 3, Canon 20mm f2.8, Sigma 35mm f1.4 Art, Sigma 50mm f1.4 Art, Canon 85mm f1.4, Tamron 24-70 f2.8, Sigma 70-200 f2.8.


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