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Manual focus to infinity

  • 17-02-2018 08:59PM
    #1
    mel.b
    Registered Users, Registered Users 2 Posts: 2,920 ✭✭✭


    I'm heading off to hopefully see & photograph the aurora next weekend. From my reading, using manual focus set to infinity is the best. Looking at my lens (Sigma 17-70) i can see a little dot that doesn't move and I can line up the infinity symbol with that and it does seem to be in focus so I am presuming that is where it should be?

    I've read about taping it to keep it in place, however my zoom ring is right next to the focus ring, so I wouldn't be able to tape it?


Comments

  • #2
    John mac
    Registered Users, Registered Users 2, Paid Member Posts: 5,173 ✭✭✭John mac


    i wouldn't rely on using the symbol alone , it can be off a tiny bit ,
    best is to manually focus on a bright star , taping it there is a good tip , ,
    you will prob be using the wide end of the zoom so tape shouldn't be a issue.
    best to refocus in the field ,
    *** practice before you go . ***

    if you have your camera set to back button focusing you might be able to focus on a distant object that will give you infinity . without having to set to manual ..


  • #3
    magicbastarder
    Moderators, Category Moderators, Arts Moderators, Sports Moderators, Paid Member Posts: 53,872 CMod ✭✭✭✭magicbastarder


    are you going to be shooting wide open?
    if not, focus becomes a little easier as the depth of field will deepen.


  • #4
    uck51js9zml2yt
    Closed Accounts Posts: 18,253 ✭✭✭✭uck51js9zml2yt


    Speaking of aurora. What aperture is recommended?


  • #5
    ED E
    Registered Users, Registered Users 2 Posts: 36,095 ✭✭✭✭ED E


    Riley Curved Mango wrote: »
    Speaking of aurora. What aperture is recommended?

    Its a big trade off depending on setup. Too long and its movements soften it, too open and you lose DoF.


  • #6
    mel.b
    Registered Users, Registered Users 2 Posts: 2,920 ✭✭✭mel.b


    So while the dog was having a run around the park tonight I had a go at trying to manual focus. Ignore the fact that camera isn't level :rolleyes:
    Have I got these in focus?

    This one I used the live view and zoomed in on the seat. I used my head torch to light it up. 4 sec, f2.8 iso 1600
    33vlq3k.jpg

    This is another . 6 sec, f2.8, iso 1600
    2uynkfs.jpg

    This one, the trees look soft to me? Am i correct in thinking, if I focus on the stars then anything in the foreground will be OOF? So I'm better to focus on something in the foreground, but maybe 20-30m away and then everything after that will be in focus?
    2ztaj5z.jpg


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  • #7
    John mac
    Registered Users, Registered Users 2, Paid Member Posts: 5,173 ✭✭✭John mac


    there's no photos attached .. :)


  • #8
    mel.b
    Registered Users, Registered Users 2 Posts: 2,920 ✭✭✭mel.b


    John mac wrote: »
    there's no photos attached .. :)

    Hmmm...I can see them :confused:


  • #9
    uck51js9zml2yt
    Closed Accounts Posts: 18,253 ✭✭✭✭uck51js9zml2yt


    mel.b wrote: »
    Hmmm...I can see them :confused:

    so can I :D


  • #10
    mel.b
    Registered Users, Registered Users 2 Posts: 2,920 ✭✭✭mel.b


    Riley Curved Mango wrote: »
    so can I :D


    That's good! Did I get them in focus ok?


  • #11
    .Longshanks.
    Registered Users, Registered Users 2 Posts: 5,718 ✭✭✭.Longshanks.


    mel.b wrote: »
    That's good! Did I get them in focus ok?

    All 3 seems to be slightly out.
    Use live view. Magnify as much as possible.
    Good rule of thumb is to dial back from infinity by ¼ to ½ mm


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