First attempt using manual focus

Discussion in 'Digital Photography' started by Ridge08, Feb 22, 2009.

  1. Ridge08 macrumors member

    Joined:
    Feb 2, 2009
    #1
    For the first time yesterday, I used the Nikkor 50mm prime f/1.8, which doesn`t autofocus on my D40. There are a lot of stray cats in my area and I stumbled on a couple of them chilling out in a pine tree that afternoon.

    Here are a couple sample photos with a few questions.

    [​IMG]
    1/200sec, f/1.8
    The face of the cat on the left is is seems pretty sharp, but the one on the right isn`t. It was probably four inches further away from the camera. Is the depth of field that shallow on f/1.8? Or did I just accidentally leave a few inches of air in front on the cats in focus too?

    -----

    [​IMG]
    1/80sec, f/3.5
    Here, I`ve gotten things the other way round: it`s now the cat on the left that`s out of focus (after it decided to stick its head forward an extra two or three inches). But the aperture is now down to f/3.5. Presumably that means a much bigger depth of field, which means I`d left a fair bit of empty space behind the cats in focus, right?

    Generally speaking, is there a guide about how great a depth of field I`ll have with each f-stop? Is there a table that says how many centimeters/meters you`ll have in focus on each f-stop? How much does this vary between lenses?

    Does anyone have any tips, beyond just practicing a lot, for learning to get sharp manual focus? I`m not sure what this could be, but maybe someone can recommend some useful exercises.

    Oh, and I also took some photos that are just slightly fuzzy round the edges and I think it creates a dreamlike quality. If you want an out-of-focus photo like this, does it make a difference whether you do it in camera or on the computer later?
     
  2. r.j.s Moderator emeritus

    r.j.s

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  3. Cliff3 macrumors 65816

    Cliff3

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    #3
    Here's a depth of field calculator: http://www.dofmaster.com/dofjs.html

    (and you need to use bbcode tags rather than HTML tags to post your images)
     
  4. Ridge08 thread starter macrumors member

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    Feb 2, 2009
    #4
    Cliff, thanks. Should be fixed now. Now I just have to work out how to post thumbnails and have them link back to Flickr.

    Edit:
    Thanks for that link!
    Looks like I had about a 3cm DoF, which explains things.

    Edit2:
    If I`d shot these in raw, would I have been able to prevent the background from being quite so blown out?
     
  5. Cliff3 macrumors 65816

    Cliff3

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    #5
    Macrumors has a timg tag you can use in place of the img tag that will produce thumbnailed images. Or, you can construct one using something like this: [ url = link to full sized image ] [ img ] url for thumbnail [ /img ] [ /url ]
     
  6. mcnicks macrumors regular

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    Jan 8, 2006
    #6
    You would see exactly the same problems with autofocus if you focused on either cat.

    Just to check, do you know that the focus indicator in the viewfinder still works when you manual focus? You should be able to point at a cat and wiggle the focus until the green light on the bottom left comes on.

    You must have been fairly close to those cats. I would have thought that f/4 plus maybe a step to the right would have gotten both of them into focus.
     
  7. r.j.s Moderator emeritus

    r.j.s

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    #7
    Agreed. f1.8 is too shallow for that, estimating that you were about 6ft away. f4 would have done the trick, possibly even f2.8
     
  8. mcnicks macrumors regular

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    Jan 8, 2006
    #8
    Just an additional thought. I don't think that the composition really works. It might have been better to choose a subject to focus on (figuratively and literally) and frame accordingly or step back and bring in more of the surroundings. Both might have resolved the depth of field issue.

    Also, you can take decent shots with the 50mm f/1.8D right down to 1/15s but only if you take lots of shots. Half of them will come out shaky but you will get one or two sharp ones. You could have walked up to those cats at f/5.6, firing away and adjusting focus and probably never have to worry about depth of field.
     
  9. Cliff3 macrumors 65816

    Cliff3

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    #9
    It seems like the cats are in shade, or at least they are considerably darker than the adjacent sky. You need to reduce the contrast between the cats and the sky, either by framing the photo differently or by using flash to provide fill light.

    FWIW, the bokeh on that lens is kind of nasty at that aperture - I would stop it down some to try to smooth it out. By way of contrast, here's a photo from an 85 f1.4 stopped down to f2.4:

    [​IMG]
     
  10. Ridge08 thread starter macrumors member

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    #10
    Mcnicks, when you say I should have chosen a subject to focus on, do you mean I should have focused on only one cat and waited for the other to get out of my way (which it did after a few minutes)?

    I mostly did take pictures that show more of the surroundings, and that have only one of the two cats in. I guess I was just trying to get up close like that to practice focusing and get an idea of the depth of field I would have.

    Agreed that it hasn`t worked so well in these two pictures. Thanks for the criticism and for the suggestions on more appropriate apertures!
     
  11. Ridge08 thread starter macrumors member

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    Feb 2, 2009
    #11
    Cliff3, yeah, the cats were in the shade of the tree. It was a sunny day and there was a large gap in the foliage behind them. I could step to the left a little and remove the bright sky from the frame, but at the expense of having the cats facing away from me. I considered using fill flash but thought they`d run away (this is the first time in six months they haven`t run away from me).

    Maybe I could have asked someone push a couple tree branches across to block the light.

    Here`s another photo I took:
    [​IMG]
     
  12. r.j.s Moderator emeritus

    r.j.s

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    #12
    The composition is better, but it looks like you missed focus by just a little bit:

    If you look, the eyes and most of the face are in focus, but the chin is not. This leads me to think the actual focus point was a few inches in front of the cat.
     
  13. Cliff3 macrumors 65816

    Cliff3

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    #13
    It might be easier to experiment on flowers ;)
     
  14. Ridge08 thread starter macrumors member

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    #14
    Agreed! :D
     
  15. namethisfile macrumors 6502a

    namethisfile

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    Jan 17, 2008
    #15
    i bet cat eyes are way faster than any lens available now.
     

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