Test of Tokina ATX AF 28-80 f2.8 (long)

Discussion in '35mm Cameras' started by Joseph Tainter, Jul 11, 2003.

  1. I bought this lens about a year ago. It got a major workout last autumn,
    when I got to spend November in France. The results have mostly been
    very, very sharp. There were, however, two images in which there was
    pronounced lateral weakness (left and right in landscape mode). I had
    not recorded the details of these images. They bothered me, so I did
    systematic tests to see if/where there was a problem. I report the
    results here.

    The subject was the old (1870) church in Corrales, New Mexico. The
    exterior is plastered in mud mixed with bits of straw; these give small
    details from which to judge sharpness. There is also a small plaque at
    9:00 indicating that the church is on the National Register of Historic
    Places. From a distance the lettering in the plaque is good for testing
    sharpness. I shot all apertures from 2.8 to 16 at 28, 35, 50, and 80 mm.
    Further details: Provia 100F, tripod, Nikon LS 2000, no image cleaning.
    I evaluated all images in Photoshop at 300% enlargement.

    Here are the results. I list sharpest to weakest f-stops from left to
    right. They are divided into three segments, based on my subjective
    classification: good (very sharp) / okay (acceptably sharp) / and weak
    (unusable). (I made the table this way because I plan to print and
    laminate it, and carry it with me.)

    You will note that at 28 mm., 4 f-stops are good and 2 are weak. None
    was in-between. At 35 mm, 3 were good and 3 were okay. None was
    unacceptable.

    Best to Worst (good/okay/weak)

    28 mm. 5.6, 4, 11, 8 / / 16, 2.8

    35 mm. 5.6, 8, 11 / 16, 4, 2.8 /

    50 mm. 5.6, 4, 8 / 2.8 / 16, 11

    80 mm. 8, 5.6, 11 / 4 / 16, 2.8

    The biggest surprise came in the 50 mm focal length. There is a
    pronounced loss of lateral sharpness between f8 and f11. The difference
    is so great that it is like suddenly falling off a cliff. At 50 mm., f11
    is unusable. Then at 50 mm. and f16, sharpness at 9:00 (the plaque)
    increases again sharply. F16 is, however, not sharp from 5:00 to 7:00.

    I have never seen anything like this result at 50 mm. and f11. Has
    anyone else? Why would sharpness at 9:00 be okay again at f16?

    Do I have a defective lens?

    The lens is still under warranty. Should I send it to Tokina? It is
    incomprehensible to me why it should be so weak at 50 mm. and f11 unless
    it is defective.

    I was thinking of selling the lens. Yet it is so sharp at its best
    apertures that I will probably keep it and use it at those apertures.

    Thanks,

    Joe
     
    Joseph Tainter, Jul 11, 2003
    #1
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  2. Joseph Tainter

    SWB Guest

    Hello Joseph
    I'm not sure what you mean by 'lateral' sharpness. Is it that the image
    falls off to the right 'and' left, and remains sharp in the centre, or that
    the image falls of 'either' to the right or left? I did a similar test to
    yours, and f11 at 50mm is very sharp. I generally agree with you overall
    comments on the lens though. Are you sure the focus didn't throw itself out
    when you tested at f11? I had to start my test again when I realized the
    lens was set on AF and was hunting slightly.
    Steve
     
    SWB, Jul 28, 2003
    #2
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