Visual abberation problem!

Discussion in 'Adapted Lenses' started by Farcanalman, Jun 15, 2012.

  1. Farcanalman

    Farcanalman  

    144
    Feb 12, 2012
    I was using my Tamron 90/2.5 earlier and noticed that in bright light, but not directly shining on it, I was seeing an abberation exactly the shape of the iris!

    When I tried a few different angles it tended to dissappear, but even after I fitted a daylight filter it still seemed to be there!

    Any ideas as to how I can get rid of this phenomenon or very much reduce its occurence?

    :confused:

    By the way, in the same place and lighting conditions, it did not occur with any of my other lenses, even the other 2 Tamrons!

    :frown:
     
  2. heli-mech

    heli-mech Mu-43 Top Veteran

    959
    Mar 9, 2012
    Vancouver Island, Canada
    Andrew
    This is a known issue with the tamron 90/2.5, most people say it has to do with no/poor coatings on the rear element(s). Are you using a hood?
     
  3. Farcanalman

    Farcanalman  

    144
    Feb 12, 2012
    Ahhh, I see!

    I did find that with the hood/filter combination there was a much reduced envelope that the abberation appeared!

    Maybe it is a task to push my discipline!

    :eek:

    The little 35-70 can do nearly the same tasking if I find that under certain conditions I cannot avoid the abberation.

    :wink:

    But does not seem to be such a problem if I really compose the shots, just cannot always be sure of that luxury!

    :rolleyes:

    We will see!
     
  4. Just Jim

    Just Jim Mu-43 Top Veteran

    941
    Oct 20, 2011
    If the hood doesn't work and you know what situations cause your issue create a cut out of something black and preferably light weight that covers the sensor ratio 4:3. place in front of lens. works a bit more than a hood will at blocking light, albeit it is a pain in the you know what as you have to move it back and forth.
     
  5. meyerweb

    meyerweb Mu-43 Hall of Famer

    Sep 5, 2011
    What you're describing is flare, and it's caused by internal reflections, generally from having a bright light source within the frame, or just outside the frame. A lens hood can help a lot, if it's well designed. Many lens hoods actually aren't long enough to work as well as they might.

    Something as simple as holding your hand out to the side of the lens to block the light can work wonders. (Of course, you need to make sure your hand is outside the picture area.) Sometimes changing your position, so the sun is coming from just a bit farther to the side, or even slightly behind you, can solve the problem.

    And using a filter will often make it worse, not better, as it adds additional glass surfaces for light to reflect off of.
     
    • Like Like x 1
  6. heli-mech

    heli-mech Mu-43 Top Veteran

    959
    Mar 9, 2012
    Vancouver Island, Canada
    Andrew
    Actually with this lens what he is describing is due to reflections of the CCD on the rear element, Google "Tamron 90mm 2.5 hotspot" and you will find other examples.