Tamron 18-400mm lens vs canon 75-300

Discussion in 'Canon EOS' started by nikkitaurus, Jul 1, 2020.

  1. Dear all,

    i Just received my new lens. Tamron 18-400mm for canon.
    i want it to replace my canon lens 75-300 for bird photography. But while Trying the lens i noticed That i was able to get closer to the subject with my 300mm lens than the 400mm Tamron.
    I really do not understand how That is possible. What did i Miss? can someone explain to me how this works?

    Thank you so much in advance!
  2. William Michael

    William Michael Moderator Staff Member

    It's not possible.

    If the bird is the same distance away from the camera, then a 400mm lens will make the bird larger in the viewfinder, than a 300mm lens - i.e. "get closer".

    I suspect that you tried the two lenses on birds which were different distances away from the camera.

    Stand at exactly the same distance from a static subject and make the comparison between the two lenses: for example, a doorway or window or tree or park bench.

  3. focus breathing was the term i heard it called as. Apparently this lens CANT go beyond 300mm until you hit a certain distance from lens to object. Comes up in alot of reviews on it
  4. William Michael

    William Michael Moderator Staff Member

    Do you mean that you were very close to the subject, i.e for a close-up shot: 14" ~ 16” (350mm / 400mm) from the Subject?

  5. I will take a stab at this even though I don't have either of the two lenses mentioned. However, I do have two previous (probably predecessor) lenses; the EF 100-300 mm USM and the Tamron 16-300 mm. A bit of optical info is helpful here. Traditionally lenses focused by moving the whole lens relative to the imaging receptor. The EF 50 mm 1.8 and 1.4 work this way. Side note: I believe that the two original f/1.2 Mk. I lenses (50 mm and 85 mm) were also unit focusing. The large amounts of glass and brass that had to be moved for focusing was the reason for their deserved reputation for slow focusing.

    Newer lens designs will often have internal focusing where some elements inside the lens move to achieve focus, with the side effect of changing the focal length of the lens at the closest focusing distances. The amount of change will depend on both the optical and mechanical design of the lens. Tony Northrup explored this in an evaluation of a few 70-200 mm f/2.8 zoom lenses; he found the Canon to be least effected, at minimum focusing distance (at 200 mm) the effective focal length was about 170 mm while one of the other zooms was at 135 mm.

    The 75-300 mm lens (original lens) is a three decades old design while the Tamron is three years old. It is likely that the Tamron has a much more pronounced focal length shift than the EF lens. In practical terms that means that if you are photographing small birds relatively close to you the Tamron may have a shorter effective focal length than the Canon. At longer distances, typically 40-50 times stated max focal length, the lenses will be close to stated focal length and the bird will be bigger with the Tamron.

    Hope this was helpful.

  6. William Michael

    William Michael Moderator Staff Member

    I might have misunderstood the question. I thought you were photographing birds at a reasonable distance.

    If you are really close to the birds, then disregard my response in post #2, and refer to tommarcus' and christian's response which makes reason if you are using the lenses very close to the birds.

    Sorry for any confusion caused.


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