User Tag List

Thanks useful information Thanks useful information:  3
Results 1 to 4 of 4

Thread: auto focus question

  1. #1
    Go the Rabbitohs mudman's Avatar
    Join Date
    23 Oct 2008
    Location
    Canberra
    Posts
    3,209
    Mentioned
    3 Post(s)
    Tagged
    0 Thread(s)

    auto focus question

    on my K7 the I use AF-C mostly and find that with either the 18-250 or the bigma that is virtually impossible to getv it to focus on infinity, evenn if i spot focus on a point way into the distance.
    my question(s) is/are:
    does the focusing system use fuzzy logic? if it does could it explain the never reaching infinity problem.
    i find this especially annoying with the 18-250 as i get unsharp detail at distances far greater than the 30 metres marked on the lens. or could it be having shake reduction on when camera on tripod?
    cc and enjoy

    Photography is painting with light

    K1, Pentax 18-250mm zoom, Pentax 100mm macro, Sigma 50-500mm, Pentax 28-105mm
    Velbon Sherpa tripod Photoshop CS6

  2. #2
    Ausphotography Site Sponsor/Advertiser OzzieTraveller's Avatar
    Join Date
    12 Oct 2009
    Location
    Forster- Tuncurry, eastern Australia
    Posts
    1,600
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    G'day Mudman

    From experience with long lenses & big-zoom lenses ... just like any other lens it should ALWAYS focus to infinity. Sometimes I have had a lens that focusses "beyond infinity" - ha ha some may say, but I have had 500 & 1000 lenses where the focus collar went a shade beyond infinity, and it gave me the confidence to know when it was at its best focus

    My current primary lens is a Leica 28-275 (much the same as yours) and it will tightly autofocus to infinity ... I can easily distinguish tree branches in a line of trees on a ridge line for instance. But when I go to manual focus, the manual-focus-aid thingy clearly shows that I can go 'beyond-infinity'

    As to fuzzy-logic ... my understanding of most auto focus systems is that they are contrast based to a large extent, most dSLRs have phase-detect focussing, (perhaps another expert can outline this one), but even so - it should focus for you

    Dunno whether this helps - hope so
    Regards, Phil
    Of all the stuff in a busy photographers kitbag, the ability to see photographically is the most important
    google me at Travelling School of Photography
    images.: flickr.com/photos/ozzie_traveller/sets/

  3. #3
    Member
    Join Date
    12 May 2009
    Location
    Cronulla
    Posts
    74
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by mudman View Post
    or could it be having shake reduction on when camera on tripod?
    I can only comment on this. I found that if I accidentally left the shake reduction on when on the tripod, I got shake. The instructions with the K10D are clear.

  4. #4
    Member
    Join Date
    16 Nov 2009
    Location
    Brisbane
    Posts
    1,831
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I can`t comment on Pentax,some Canon IS lenses(older versions)will produce "shake" on a tripod,it doesn`t happen with my IS lenses,but I turn it off anyway.
    Kev.
    C+C and Edits Welcome,just tell me what you did.
    Canon 50D,EF-S17-85mm,EF100mm F2.8 Macro,MT-24EX Flash.
    Sigma 150-500mm f5.6-6.3 DG.
    Photoshop Elements 7


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •