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Distance scale on Nikon 18-70mm zoom lens - Photography

I don't know why I didn't notice this before but... It seems that the distance scale on the Nikkor DX 18-70mm lens (the lens that comes with the D70 as a kit) is set to be accurate only at maximum telephoto. When set to widest wide-angle, the distance scale is quite a way off. I did a test on maximum wide angle with a subject (practically) at infinity. The distance when autofocussed was (according to the scale) closer to the 2m mark than the infinity mark. (I know the scale isn't linear, but was still suprised where the autofocus seemed ...

  1. #1

    Default Distance scale on Nikon 18-70mm zoom lens

    I don't know why I didn't notice this before but...


    It seems that the distance scale on the Nikkor DX 18-70mm lens (the
    lens that comes with the D70 as a kit) is set to be accurate only at
    maximum telephoto. When set to widest wide-angle, the distance scale
    is quite a way off. I did a test on maximum wide angle with a subject
    (practically) at infinity. The distance when autofocussed was
    (according to the scale) closer to the 2m mark than the infinity mark.
    (I know the scale isn't linear, but was still suprised where the
    autofocus seemed to end up.) The image came out fine. I also tried
    manual-focussing and set the focus by setting the distance scale to
    infinity. This second image was noticeably out of focus.

    I'd already noticed that if a subject is in focus at a particular
    focal length, changing the zoom doesn't move the focus ring and the
    image goes out of focus. I assumed this is standard behaviour; but it
    didn't occur to me until now that this implies that the distance scale
    only works at a particular focal length.

    Could someone set my mind at rest and confirm that the lens is
    behaving as expected? The last time I used an SLR, I had separate wide
    and telephoto lenses, and it's a bit embarrassing to confess to this
    level of ignorance regarding zoom lenses.

    Thanks.
    Gary Guest

  2. #2

    Default Re: Distance scale on Nikon 18-70mm zoom lens


    "Gary Jones" <com> wrote in message
    news:google.com... 

    Keep in mind that when set to wide angle you get a heck of a lot of depth of
    field, so the focus can be way off but the image, and everything around it,
    will still be in focus. I'm not sure how the camera decides to focus on
    anything, but maybe it's trying to give you the max depth of field,
    especially when using small apertures. This is just a hunch on my part,
    BTW.


    Sheldon Guest

  3. #3

    Default Re: Distance scale on Nikon 18-70mm zoom lens

    On Mon, 31 Jan 2005 21:21:53 -0700, in rec.photo.digital.slr-systems
    "Sheldon" <net> wrote:

     

    It depends on the modes and Focus Area settings. In many scene modes
    closest subject is chosen. To enable manual selection set Custom 3,
    AF-area mode to single or dynamic. Read pp 64-69 of the manual.
    ----------
    Ed Ruf Lifetime AMA# 344007 (Ruf.com)
    See images taken with my CP-990/5700 & D70 at
    http://edwardgruf.com/Digital_Photography/General/index.html
    Ed Guest

  4. #4

    Default Re: Distance scale on Nikon 18-70mm zoom lens

    Gary Jones wrote: 


    There could be a simple answer to this. Your "zoom" lens is in fact
    "varifocal", meaning that the point of focus changes as you zoom.

    I have one lens that does this - it is a Pentax 35-105mm "zoom". There
    is a very big difference between the infinity focus position at 35mm
    and at 105mm. The explanation is that this lens is a "varifocal"
    design.

    A true "zoom" lens does not do this. It keeps the point of focus the
    same as you zoom. But it is probably cheaper to make "varifocal"
    lenses ... and if you use autofocus, the change in focus point doesn't
    bother you. Of course my Pentax lens is not autofocus ... I was very
    worried when I first bought it. It was a second hand lens and I
    thought it had maybe been dropped. But it is OK. I bought another
    used one in almost new state and its focusing is exactly the same.

    So do not worry. Just take some care when focusing manually and
    looking at depth of field.

    SMC Guest

  5. #5

    Default Re: Distance scale on Nikon 18-70mm zoom lens

    SMC wrote: 
    >
    >
    > There could be a simple answer to this. Your "zoom" lens is in fact
    > "varifocal", meaning that the point of focus changes as you zoom.
    >
    > I have one lens that does this - it is a Pentax 35-105mm "zoom".
    > There is a very big difference between the infinity focus position at
    > 35mm and at 105mm. The explanation is that this lens is a "varifocal"
    > design.
    >
    > A true "zoom" lens does not do this. It keeps the point of focus the
    > same as you zoom. But it is probably cheaper to make "varifocal"
    > lenses ... and if you use autofocus, the change in focus point doesn't
    > bother you. Of course my Pentax lens is not autofocus ... I was very
    > worried when I first bought it. It was a second hand lens and I
    > thought it had maybe been dropped. But it is OK. I bought another
    > used one in almost new state and its focusing is exactly the same.
    >
    > So do not worry. Just take some care when focusing manually and
    > looking at depth of field.[/ref]

    From the booklet supplied with Canon's EF24-70mm f/2.8L USM lens (not
    cheap):
    "(!) Be sure to finish zooming before focusing. Changing the zoom ring
    after focusing can affect the focus."

    Which lenses do _not_ show this effect?


    --
    Frank ess

    "Because of the Swiss Cheese nature of everyone's life experience and
    education, the Whoosh Bird can drop a load on anyone's head, without
    warning." -Albrecht Einstein


    Frank Guest

  6. #6

    Default Re: Distance scale on Nikon 18-70mm zoom lens

    Frank ess wrote:
     

    Two would be the Maxxum 28-70 and 80-200 f/2.8's 'hold' their focus during zoom.
    However, if you focus at the wide end and then zoom in, the error from the
    wide end focus appears and a slight tune is needed to get it perfect. Going the
    other way (narrow to wide) there is no discernible error, of course.

    By error I mean the error of the eye or the AF. What is not perceptible as a
    focus error wide shows up when you zoom in more detail.

    I suspect the same meaning applies to what you quoted above.

    Cheers,
    Alan



    --
    -- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
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    -- [SI] gallery & rulz: http://www.pbase.com/shootin
    -- e-meil: there's no such thing as a FreeLunch.
    Alan Guest

  7. #7

    Default Re: Distance scale on Nikon 18-70mm zoom lens

    In article <com>,
    Frank ess <com> wrote: 
    >>
    >>
    >> There could be a simple answer to this. Your "zoom" lens is in fact
    >> "varifocal", meaning that the point of focus changes as you zoom.
    >>
    >> I have one lens that does this - it is a Pentax 35-105mm "zoom".
    >> There is a very big difference between the infinity focus position at
    >> 35mm and at 105mm. The explanation is that this lens is a "varifocal"
    >> design.
    >>
    >> A true "zoom" lens does not do this. It keeps the point of focus the
    >> same as you zoom. But it is probably cheaper to make "varifocal"
    >> lenses ... and if you use autofocus, the change in focus point doesn't
    >> bother you.[/ref][/ref]

    [ ... ]
     

    Are you asking about the Cannon in particular? The "Subject: "
    header refers to the Nikon lens which comes with the D70 kit. I have
    the D70, but with a:

    28-104mm AF Nikkor 1:3.2-54. D

    and this does not show this behavior.

    Neither does the 70-205 mm Nikor which I seldom use with this
    camera, simply because it does not have the CPU, so I am back to a
    handheld meter with it*. And the fellow who does the CPU conversions
    does not want to handle converting this lens (I guess bad experience
    with another), so I guess that I am stuck here. (Unless Nikon will
    convert them?)

    *) A handheld meter is not a real problem (other than convenience)
    with shorter lenses, but this puts me a bit too far out to be
    convenient. Especially since I am likely to be shooting
    subjects which would be spooked if I walked up to meter them
    properly with a handheld.

    Enjoy,
    DoN.
    --
    Email: <com> | Voice (all times): (703) 938-4564
    (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
    --- Black Holes are where God is dividing by zero ---
    DoN. Guest

  8. #8

    Default Re: Distance scale on Nikon 18-70mm zoom lens

    In article <ctr9mc$obi$d-and-d.com>,
    DoN. Nichols <com> wrote: 

    [ ... ]
     [/ref]

    [ ... ]
     

    Oops! I meant 80-200mm Nikor (after checking it).

    Enjoy,
    DoN.
    --
    Email: <com> | Voice (all times): (703) 938-4564
    (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
    --- Black Holes are where God is dividing by zero ---
    DoN. Guest

  9. #9

    Default Re: Distance scale on Nikon 18-70mm zoom lens

    DoN. Nichols wrote: [/ref]
    >
    > [ ... ]

    >
    > Are you asking about the Cannon in particular? The "Subject: "
    > header refers to the Nikon lens which comes with the D70 kit. I have
    > the D70, but with a:
    >[/ref]

    Just curious about how important such a consideration is to lens
    sellers. I'm certain designers know its value.

    I remember learning early in my pre-digital life to focus at long zoom
    and go wider from there. Were old-time film zooms less subject to the
    drift?

    Come to think of it, I _would_ like to know about current Canon lenses'
    tendencies. Maybe I'll start a thread ...

    Meantime, thank you for the information.

    <snip information>


    --
    Frank ess


    Frank Guest

  10. #10

    Default Re: Distance scale on Nikon 18-70mm zoom lens

    In article <com>,
    Frank ess <com> wrote: [/ref]

    [ ... ]
     
    >>
    >> Are you asking about the Cannon in particular? The "Subject: "
    >> header refers to the Nikon lens which comes with the D70 kit. I have
    >> the D70, but with a:
    >>[/ref]
    >
    >Just curious about how important such a consideration is to lens
    >sellers. I'm certain designers know its value.
    >
    >I remember learning early in my pre-digital life to focus at long zoom
    >and go wider from there. Were old-time film zooms less subject to the
    >drift?[/ref]

    This is more than just drift, I think. *Good* old time lenses
    were carefully crafted to maintain focus from maximum effective focal
    length to minimum. Obviously, going the other way, you have a bit of a
    handicap, as it is difficult to focus as well at minimum effective focal
    length.

    These days, with good autofocus available, the camera
    manufacturers can simplify the design of the lens a bit, knowing that
    the camera will touch up the focus when you reach your desired focal
    length and start to take the shot.
     

    It will be interesting to see what you get, there.
     

    You're welcome.

    Enjoy,
    DoN.

    --
    Email: <com> | Voice (all times): (703) 938-4564
    (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
    --- Black Holes are where God is dividing by zero ---
    DoN. Guest

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