Is my lens' infinity focus out of calibration?

Discussion in 'Adapted Lenses' started by ChurchWithoutBalls, Jan 4, 2013.

  1. ChurchWithoutBalls

    ChurchWithoutBalls New to Mu-43

    4
    Jan 4, 2013
    I just got a Vivitar Series 1, 28mm-90mm 2.8-3.5 FD mount macro lens. I have never had this kind of lens before so I am not sure if it is supposed to be doing what it is doing.

    At 28mm (zoomed all the way out) and F/2.8 with focus on infinity, my point of focus is 46 inches from the end of the lens. In other words, at 28mm, I cannot focus on anything further than 46 inches away. I can focus closer - all the way up to about a centimeter from the end of the lens. Of course changing my F-stop to 8, extends the DoF so that I can focus as far at 15-18 feet away but as I want to be able to shoot in lower light situations with a wide angle, stopping down is not an option for me.

    I want to know if this is what the lens is supposed to do. My experience with non-macro video lenses tells me that at infinity, my focal point should be somewhere around a half mile away, give or take. Is this lens, because it is a macro, designed to do this or is it out of calibration for its infinity point? If it is "broken" is there a way to fix it?

    I am using the FD adapter and my other prime lenses all function properly, focusing far away at infinity.

    Thanks for the help.
     
  2. addieleman

    addieleman Mu-43 All-Pro

    Aug 5, 2010
    The Netherlands
    Ad
    The lens could be at fault, but your adapter may be a bit too long as well. If you use a cheap-ass adapter from China like I do, try to tighten the screws (if any) on the FD bayonet mount. Or order another adapter, I order them with this seller and they are mostly a bit short, meaning that the lens is able to "focus past infinity" and that is not a problem unless you want to do scale focussing. For the record, I'm not in any way associated with the seller.
     
  3. kinlau

    kinlau Mu-43 Top Veteran

    836
    Feb 29, 2012
    It's most likely the adapter.
     
  4. ChurchWithoutBalls

    ChurchWithoutBalls New to Mu-43

    4
    Jan 4, 2013
    not the adapter

    I am using the Fotodiox FD-m4/3 adapter. I can focus properly to infinity (maybe a little past) using my prime lenses.

    I mounted the lens to my old AE-1 to check if it was the adapter (the AE-1 needs no adapter as it is an FD mount camera) and the lens is responding with the same focus issue. It focuses at 46 inches from the lens at 28mm and f/2.8.
     
  5. meyerweb

    meyerweb Mu-43 Hall of Famer

    Sep 5, 2011
    To answer the original question, no, the lens is not supposed to act that way. It's clearly defective.
     
  6. ChurchWithoutBalls

    ChurchWithoutBalls New to Mu-43

    4
    Jan 4, 2013
    Thank you! That is what I thought, but always good to ask and find out for sure.
     
  7. dwig

    dwig Mu-43 Top Veteran

    623
    Jun 26, 2010
    Key West FL
    This is useless information as stated. If you can provide us with the focal lengths of these "other prime lenses" there might be some lead as to the source of your problem with the Vivitar.

    There are two possible sources for your problem and it's possible that both are involved:

    • The lens is improperly assembled: Unskilled DIY repair jobs can lead to this.
    • Adapter is too long/thick: This will extend the lens from its intended position causing all lenses to focus closer than they would on an accurate body or accurate adapter. The degree to which this will affect the focus is inversely proportional to the lens' focal length. The shorter the FL the greater the error. It's quite possible for an error to be significant on a short FL lens and unnoticed on a noticably longer lens.

    Recheck your other lenses testing to see what their actual focusing distances are when set to infinity. If they all error to focusing closer than marked and if the errors follow a pattern of the longer lenses focusing further away then it's certain that your adapter is faulty. Your 28-90 may still also be faulty but you can't confirm without a proper adapter.

    Most adapters are designed to be slightly thinner than what is theoretically proper. This is to prevent the manufacturing variance inevitable in inexpensive manufacturing from preventing lenses from focusing to infinity. The error you describe is rather large and if it's solely the result of the adapter being out of spec then you should be seeing the error in other lenses.
     
  8. ChurchWithoutBalls

    ChurchWithoutBalls New to Mu-43

    4
    Jan 4, 2013
    I mounted the lens on my canon AE-1 (no adapter needed as it is a native FD camera) and the lens exhibited the same issue. That tells me the lens is out of alignment internally.