Nikon 500mm mirror on D70 - help with focus

Discussion in 'Digital Photography' started by Mark, Jun 7, 2004.

  1. Mark

    Mark Guest

    I've got a Nikon D70 on which I've mounted an old Nikkor 500mm f8 mirror
    lens. Exposure isn't a problem - put it in manual and guess at the
    shutter speed / ISO until the histogram looks reasonable.

    The problem that I'm having is with getting a sharp focus. The D70
    doesn't have any focusing aids for a manual focus lens. I'm able to get
    close, but I just haven't been able to get a sharp focus (I'm currently
    trying to take pictures of birds at feeders from about 30 feet away).

    Any ideas as to how best to achieve a sharp focus with this camera /
    lens combination?

    Mark
     
    Mark, Jun 7, 2004
    #1
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  2. Mark

    Jimmy G Guest

    I seem to recall reading someplace that some, or all, mirror lenses will
    not work well with autofocus cameras. I believe it has something to do with
    the reflective, catadioptric design and how light is interpreted by the
    focusing sensor. You also must use circular polarizer with autofocus for
    similar reasons.

    That's about as technical as I can get. Anybody else have any ideas?
     
    Jimmy G, Jun 7, 2004
    #2
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  3. Mark

    B.A.S. Guest

    But I think the poster is saying that he's not using the focusing
    sensors - he's just trying to do completely manual focusing via what he
    sees in the viewfinder.

    In general, this is a tough thing to do on a modern AF SLR with no
    focusing aids (split image, fresnel or matte screen, etc,) and a dim
    viewfinder.

    Mark - are you saying when you focus by eye, the resulting image is out
    of focus? Or are you saying even if you twiddle the focus back and forth
    in subsequent shots, there is NO focus setting at which the resulting
    image will be in focus?

    B.A.S.
     
    B.A.S., Jun 7, 2004
    #3
  4. << The problem that I'm having is with getting a sharp focus. The D70
    doesn't have any focusing aids for a manual focus lens. >>

    Mark-

    Try holding something like a finger, a pencil or a popsicle stick in front of
    the lens, just touching the front of the lens barrel. You may be able to see
    an effect where two images are produced by the light from both sides coming
    through different parts of the lens, resulting in a "split image" of sorts. An
    object is in focus when the lens is adjusted so that both pieces of its image
    come together.

    The effect depends on the object having just the right width. If it is too
    wide, the image is split in half. If it is too narrow, the images pieces don't
    spread far enough apart to be recognized.

    The effect also works when projecting an image on a screen. I've found it to
    be quite handy when setting up a slide projector.

    Fred
     
    Fred McKenzie, Jun 7, 2004
    #4
  5. Mark

    Steve West Guest

    I'm confused. 35mm cameras with pentaprism focussers allowed excellent
    manual focus. I thought the DSLR with TTL focussing provides the same
    capability? Is there not ground glass behind the pentaprism or do they put
    an LCD monitor in there? Gosh, I thought the DSLR was going to finally end
    the nightmare of impossible manual focussing with digicams...

    Thanks

    Steve
     
    Steve West, Jun 7, 2004
    #5
  6. Mark

    Guy Scharf Guest

    The DSLRs I have seen have a "clear sight" but not a focusing screen
    with microprism or split image focusing. Coupled with my eyesight
    problems, I don't try to manual focus on my D70 except for macro work
    (with a manual lens).

    Guy
     
    Guy Scharf, Jun 7, 2004
    #6
  7. Mark

    Jose Marques Guest

    Another problem is that Nikon's autofocus system works with lenses that
    are f/5.6 or faster. The 500mm mirror is f/8 I think.
     
    Jose Marques, Jun 7, 2004
    #7
  8. Mark

    Mark Guest

    I'm focusing by eye. I bring the focus in from infinity, stopping when
    I think I have a clear image in the viewfinder. In this case, the lens
    was mounted to a sturdy tripod, so camera shake shouldn't be much of an
    issue. I can get close - the scaled-down image at 1024x768 or so on my
    computer monitor looks pretty good, but once you look at 'actual pixels'
    you can clearly see that the image isn't sharp.

    I had the same problem with this lens trying to take pictures of the
    moon - I could get the image looking pretty sharp in the viewfinder, but
    never got an image I liked on screen.

    I've gotten excellent pictures with this lens and my Nikon EM (!), which
    has a split-image manual focus system that lets you achieve sharp focus.
    I never really tried my 6006, which has no manual focus aids -
    essentially the same as the D70 in that regard. The advantages of
    digital are great enough that I got out the old lens and decided to give
    it a try on the D70.

    I don't know if I just need more practice knowing what it looks like
    when I do get something in focus, or if there is a technique to help.

    Mark
     
    Mark, Jun 7, 2004
    #8
  9. I'm not sure it's possible. I have an N70 and an N90, and like most AF
    SLR's the finder is optimized for brightness rather than manual focus
    ability.

    I actually went to the store last week check in hand for a D70, but
    decided to wait after I tried it with my lenses. The finder is MUCH
    worse than my film SLRs, and I just couldn't see trying to manually
    focus it. Worst case was a 400mm f/5.6; your 500mm F/8 must be a
    nightmare.

    BTW, the D100 I looked at was about like my N90; tough to manually
    focus but do-able. Now I'm saving up another $500.....
     
    Scott Schuckert, Jun 7, 2004
    #9
  10. Mark

    jaf Guest

    Hi Mark,
    I've found that no tripod is sturdy enough for 500mm or above. Sandbag it!
    Keep in mind your getting an effective 750mm from the setup.

    Nikon makes a right angle (DR-6) and a straight magnifier (DG-2) that will
    fit any Nikon with an eyepiece adaptor.
    Works well for sharp focusing.


    --
    John
    johnf 202 at hotmail dot com


    | B.A.S. wrote:
    |
    | > Mark - are you saying when you focus by eye, the resulting image is out
    | > of focus? Or are you saying even if you twiddle the focus back and forth
    | > in subsequent shots, there is NO focus setting at which the resulting
    | > image will be in focus?
    |
    | I'm focusing by eye. I bring the focus in from infinity, stopping when
    | I think I have a clear image in the viewfinder. In this case, the lens
    | was mounted to a sturdy tripod, so camera shake shouldn't be much of an
    | issue. I can get close - the scaled-down image at 1024x768 or so on my
    | computer monitor looks pretty good, but once you look at 'actual pixels'
    | you can clearly see that the image isn't sharp.
    |
    | I had the same problem with this lens trying to take pictures of the
    | moon - I could get the image looking pretty sharp in the viewfinder, but
    | never got an image I liked on screen.
    |
    | I've gotten excellent pictures with this lens and my Nikon EM (!), which
    | has a split-image manual focus system that lets you achieve sharp focus.
    | I never really tried my 6006, which has no manual focus aids -
    | essentially the same as the D70 in that regard. The advantages of
    | digital are great enough that I got out the old lens and decided to give
    | it a try on the D70.
    |
    | I don't know if I just need more practice knowing what it looks like
    | when I do get something in focus, or if there is a technique to help.
    |
    | Mark
     
    jaf, Jun 7, 2004
    #10
  11. Mark

    Mark Guest

    I know - 750mm is a great idea, if you can get it focused!
    I'd be interested in trying one - I'll have to see if my local camera
    store stocks them. It's a US $50-60 option, or about 1/5 what I paid
    for the lens itself!

    Thanks for the help.

    Mark
     
    Mark, Jun 8, 2004
    #11
  12. This is far fetched but you might try a technique used on astronomical
    catadioptics. Get a cheapie lens cover and drill/cut/bore/chew three
    equally spaced holes spaced 120 degrees apart on the greatest radius
    that the lens will "see".

    Place this over the lens and focus until the three images merge into
    one.
     
    The Kenosha Kid, Sep 23, 2004
    #12
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