How to test for Infinity Focus?

Discussion in 'Adapted Lenses' started by digitalandfilm, Feb 15, 2013.

  1. digitalandfilm

    digitalandfilm Mu-43 All-Pro

    Jul 18, 2011
    I have two adapters and I am wondering how to check that my adapter allows proper focus to infinity?

    The adapters are Photodiox and Novoflex M42->m4/3rds

    The lens is the CZJ Flektogon 35mm F2.4

  2. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Real Name:
    Sean Rastsmith
    Um, I am going to say the obvious.

    Find something that is very very far away, and see if it focuses on it, without either not getting to it, or is blurry after.
  3. fin azvandi

    fin azvandi Mu-43 All-Pro

    Mar 12, 2011
    Madison, WI
    Right, you want to be able to focus on something extremely far away. Usually you will be able to get it in focus and then continue to turn the lens a bit more and the distant target will go back out of focus. This is "focusing past infinity" that you see mentioned related to adapted lenses, and it has to do with the adapter not being 100% the correct size to replicate the lens-to-film distance for that mount.

    Better to be able to focus past infinity than not get there in the first place.
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  4. RichDesmond

    RichDesmond Mu-43 Veteran

    Nov 18, 2011
    A full moon makes a good target. :smile:
  5. digitalandfilm

    digitalandfilm Mu-43 All-Pro

    Jul 18, 2011
    That is what I'm experiencing.. hopefully the novoflex will resolve this.

    Is it possible to tighten a M42 screw mount too tight and cause this symptom?
  6. RobWatson

    RobWatson Mu-43 Hall of Famer

    Lacking infinity (and, no, the moon actually does not exactly work) you can set the lens (presuming it has distance scales) to a specific distance then put an object at that distance and check for accurate focus. Measure the distance from the sensor plane to the object. Always work with the aperture wide open.

    Works best for ~10 meters or there abouts (or whatever is the maximum numerical mark on the lens).

    With zoom lenses same process but zoom in and out to verify parfocality.

    Note that a "good" adapter at F4 will likely not be good at F2, etc.

    Also note that some lenses may not actually be correctly configured ... used legacy glass that some 'expert' has reassembled can be quite perplexing here.
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  7. RichDesmond

    RichDesmond Mu-43 Veteran

    Nov 18, 2011
    That's normal.