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Focus beyond infinity?

Discussion in 'Panasonic Cameras' started by gccxo, Aug 6, 2013.

  1. gccxo

    gccxo New to Mu-43

    4
    Aug 6, 2013
    Chester UK
    My G3 with a 14-140mm Pan lens seems to focus beyond infinity. :eek::eek: I noticed it in the viewfinder and on the LCD screen when using manual focus. When focusing on infinity according to the focus guide, I noticed that distant details became less clear on the display, but became sharper as I brought the focus back a little.

    So I took several pictures first focused on infinity (ie focus guide fully to the left), and then with the focus brought slightly closer (a couple of millimeters to the right each time on the guide). I found that the resulting images showed the same as the screens - the sharpest distant detail was on the pictures taken with the focus guide not on infinity!

    Has anyone else noticed this? Maybe my lens is faulty, in which case I'll have to send it back under guarantee.

    Thanks.
     
  2. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Sean Rastsmith
    Yes, this is a well known problem. They allow a slight focus beyond infinity to insure that it is always reachable, even with temperature variations. The downside is there is no way (that I know of) to adjust these to stop where it actually hits infinity (unlike some of the old manual glass I have).
     
  3. RT_Panther

    RT_Panther Mu-43 Legend

    May 4, 2011
    Texas
    [ame=https://www.youtube.com/watch?v=cZh105_r2Qk]AT&T TV Commercial - It's Not Complicated "Infinity" - YouTube[/ame]
     
  4. entropicremnants

    entropicremnants Mu-43 All-Pro

    Jul 16, 2012
    John Griggs
    Focusing beyond infinity is the "Buzz Lightyear" technique...
     
    • Like Like x 1
  5. sinclair

    sinclair Mu-43 Veteran

    Point it at the moon and try focusing on it. Can you focus past it?
     
  6. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Gordon
    Heat allowance plays a very small part now days. Modern plastics and alloys don't freak out that much to be an issue. It's just that most lenses are varifocal designs and need that slop at infinity to be able to be focused at various focal lengths. Then add a bit more for the AF mechanism. AF motors definitely don't like sudden mechanical stop points. It kills them real fast. Most non AF primes have no focus past infinity. Like the Voigtlanders for example.

    A zoom lens that maintains focus during zooming is called a parfocal lens.

    Parfocal lens - Wikipedia, the free encyclopedia

    Gordon

    Gordon
     
  7. RobWatson

    RobWatson Mu-43 Hall of Famer

    My Voity 25mm F0.95 goes well past infinity ... I don't know why. Kind of a pain actually.

    Contrast based AF needs to go beyond a bit to find infinity. Perfectly normal.
     
  8. mister_roboto

    mister_roboto Mu-43 Top Veteran

    637
    Jun 14, 2011
    Seattle, WA, USA
    Dennis
    Yeah my Nokton 25mm does too. As does the aluminum Olympus manual focus ring lenses- which can be really annoying when zone focusing.
     
  9. tjdean01

    tjdean01 Mu-43 Top Veteran

    842
    Feb 20, 2013
    Every single lens I have focuses past infinity, even the native ones when I use them on MF. To top that, some of my lenses focus closer by going clockwise, others by counter-clockwise. I focus every shot anyway when I'm in MF so no biggie. I always have AF for lazy days :tongue:
     
  10. Djarum

    Djarum Super Moderator

    Dec 15, 2009
    Huntsville, AL, USA
    Jason
    On all the mft lenses I own, yes.
     
  11. RobWatson

    RobWatson Mu-43 Hall of Famer

    Interestingly enough even with a perfectly focused moon shot note that stars are still not in focus! Moon is far but stars are farther and infinity is a bit beyond that even!
     
  12. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Gordon
    Hmmm. I've never noticed that. I've been calibrating my rangefinders infinity point on the moon for years based on common advise. I'll have to pay more attention to that.

    Gordon
     
  13. gccxo

    gccxo New to Mu-43

    4
    Aug 6, 2013
    Chester UK
    Focus past infinity

    Thanks for all your comments.

    I'm new to DSLRs, and I suppose I compare everything to the many film SLRs I had in the past. On those, no lenses focused past infinity (well, none that I had anyway). I can imagine a need to do it with autofocus I guess. I noticed this at an air show and the autofocus was having trouble focusing on aircraft in the air so I was missing shots as the focus hunted around, so I went to manual. Normally I'd just have turned the focus ring to its stop, but then found this "problem".

    Learning all the time! :thumbup:
     
  14. gccxo

    gccxo New to Mu-43

    4
    Aug 6, 2013
    Chester UK
    Re the moon, I'm surprised your depth of field can differentiate focus between the moon and stars! I'd have thought you'd need a really long focal length and big telescope to do that. I was using trees in the distance, maybe a mile away, as my "infinity" object.
     
  15. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Gordon
    Yeah. I have a perfectly calibrated leica M9 that I hand calibrated using a test chart and a tower 2-3kms away for infinity. That camera has perfect focusing with every lens I've put on it, including three faster than f1.2 and the notoriously difficult to focus 135mm f3.4 APO. I've always believed (rightly or wrongly) that infinity is at about 50 times the focal length of the lens. After that DOF makes it all but impossible to see a difference.

    However I've never bothered to "prove" my beliefs about this, so I may be mistaken. I would have thought that any blur when focused on the moon would have to do with the speed of the Earths rotation. But again. I've never looked to prove it via any texts.

    Gordon
     
  16. Djarum

    Djarum Super Moderator

    Dec 15, 2009
    Huntsville, AL, USA
    Jason
    Yup. I do find it interesting though that I don't run into this issue with my telescope. The moon and stars focus at the same point. Maybe a depth of focus thing.
     
  17. dwig

    dwig Mu-43 Top Veteran

    622
    Jun 26, 2010
    Key West FL
    The only "problem" with this is that the user doesn't understand that this is normal and mandatory behavior.

    To expect an AF lens, particularly one designed for a contrast based AF system, to stop its focus travel at exactly infinity show a lack of understanding of how the AF system works.
     
  18. dhazeghi

    dhazeghi Mu-43 Hall of Famer

    Aug 6, 2010
    San Jose, CA
    Dara
    Nope, this is standard behavior with almost all modern lenses.

    What makes it annoying is that in poor lighting it's hard to get accurate infinity focus. When doing night scenes I often have to AF on the moon or some other bright distant object, and then switch to MF and pray that I don't jog the focus ring accidentally. Not a great way to do things.
     
  19. entropicremnants

    entropicremnants Mu-43 All-Pro

    Jul 16, 2012
    John Griggs
    There really isn't any such thing as "infinity focus" -- it's not an arbitrary hyperfocal point in space. But as somebody mentioned, when you get focused out to a certain point, just about anything you want from that point on is in focus due to the huge relative DOF.

    However, home telescopes have relatively small apertures, and you are LOOKING DIRECTLY THROUGH THE LENS WITH YOUR OWN EYES. This means that YOUR EYE is part of the focusing mechanism. Just like looking through an OVF (not an SLR type -- that's a projection system) but an old style OVF. Everything is always in focus because your own eye focuses on it.

    Put a camera on your telescope and things change. Getting large aperture telescopes like at big observatories and the Hubble telescope requires precise focusing just like for terrestrial camera work.
     
  20. janneman

    janneman Mu-43 Veteran

    414
    Dec 6, 2012
    Netherlands
    Jan (John) Kusters
    From what I recall back in the late seventies and early eighties, the first lenses focusing past infinity were the Canon tele primes that had fluorite lens elements for correcting chromatic aberration. The elements were temperature sensitive, hence the 'past infinity' focus. I expect the reason for focusing past infinity is at least partial still the same.