Can a lousy filter affect focus?

Discussion in 'Panasonic Cameras' started by RajC, Aug 25, 2013.

  1. RajC

    RajC Mu-43 Regular

    Jul 6, 2013
    Recently, I took out my G5, kit zoom and 45-200 mm lens. The 45-200 mm was having trouble focusing at a distance, but seemed to do ok on subjects that were closer.

    Later, trying to troubleshoot, I took off the polarizer and it seemed to work fine.

    My questions:
    Does a polarizer affect autofocus?
    Does a cheap polarizer affect autofocus?

    The filter that seemed to be the problem is a Nicna Pro1-D Wide Band Pro-MC C-PL(W) from Rainbow Images. It wasn't very expensive but, if it affects focus, it is worthless.

    My other polarizer, a Rocketfish CPL from Best Buy seems fine.

    My plan was to have polarizers on each lens, since nearly all of my shooting is outdoors.

    Anyone else have similar issues, including this brand?
  2. blueeyedpop

    blueeyedpop Mu-43 Rookie

    Aug 17, 2013
    Agoura Hills, CA
    The longer the lens, the more a filter can affect the image quality.

    Some digital cameras were sensitive to polarization, that is why people switched to circular polarizers. I don't think this is an issue with mirrorless cameras.
  3. flash

    flash Mu-43 Hall of Famer

    Apr 29, 2010
    1 hour from Sydney Australia.
    Two issues here. Firstly, yes a cheap filter can affect AF. The af can only detect contrast as well as the light coming down the lens allows it to. Lower the contrast with a cheap filter and get less consistant af. Secondly all AF systems have a minimum amount of light where they work properly. Your lens is already at f5.6 at the long end. The polariser darkens this between 1.5 and 2.5 stops. AT some point the AF can't work in light that dim.

    I would suggest that the one that didn't work is a bit darker than the one that did. Enough to push the AF system over the edge. Possibly combined with poor quality glass in the filter itself.

    Although the 45-200 is relatively cheap, it's a pretty good lens, optically. A better quality filter may cost half as much as the lens itself, but it's worth it. In filters you definitely get what you pay for.

  4. RT_Panther

    RT_Panther Mu-43 Legend

    May 4, 2011
  5. RajC

    RajC Mu-43 Regular

    Jul 6, 2013
    Good info

    I appreciate the comments and links.
    I'll try a few more tests. Maybe the cheap filter would do well (affect IQ less and be able to focus) on the wider kits lens.

    I should have mentioned the conditions were very good, light-wise: outdoors at a wildlife refuge in bright sun, shortly before noon.
    Also, when I tried manual focus I wasn't able to get a clear image, either. I should say that the image wasn't clear enough in the viewfinder to take a shot. I don't know how the image would have turned out had I squeezed the shutter release.
  6. bg2b

    bg2b Mu-43 Regular

    Dec 22, 2009
    Berkeley Heights, NJ
    I've had similar issues with a GH2 and 45-200, though in my case using a cheap ND filter (in bright sun). No filter, no focus problems; with filter, difficulty locking focus at the far end of the zoom. The same ND filter gave no focus problems on a 14-45.
  7. metalmania

    metalmania Mu-43 Veteran

    Jul 19, 2012
    No necessarily "cheap" filter. I have some Hoya ND filters. Put it on Panasonic 25/1.4, most of the time I don't have focus problem, however I did encounter some problems if shooting portraits. If I put the ND filter on 45/1.8, well all the hell breaks loose, not even one picture can be focused right.

    So no more ND filters for me, cheap or expensive whatever. I am waiting for the GX7 to use my fast lenses.
  8. RajC

    RajC Mu-43 Regular

    Jul 6, 2013
    I've contacted Panny to see what the official line is. I'll post the reply.

    Very happy to hear others have had similar problems.
    I guess the solution is to focus manually, put on filter, set exposure then snap the shot.
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