Questions about extension tubes

Discussion in 'Digital SLR' started by Graham Holden, Mar 17, 2005.

  1. A few questions that I hope those with more experience than I can answer:

    I've got a Nikon D70 and the 50mm f/1.8 lens and am thinking of getting
    some extension tubes as a "poor man's macro". I know they allow you to
    focus closer, and therefore fill the frame with a smaller subject, but how
    much closer/larger can you get? (I'm looking at the Kenko set -- 12mm +
    20mm + 36mm).

    The Kenko set says it allows auto-focus (except for AF-S lenses) and
    metering (except the "D" information); does anyone know if Jessop's "own
    brand" set also allows this? Any comments on the quality between the two?

    I believe extension tubes' effects are most dramatic for shorter
    focal-length lenses, but could I expect anything useful with a 70-300mm
    zoom lens (i.e. for longer distance close-ups)?

    Do you consciously have to make exposure adjustments when using extension
    tubes, or is this all catered for with the metering? (I know you lose
    light, because of the tubes, but I would guess the metering will have taken
    this into account).

    Anything else I need to know about?

    Thanks in advance for any help.


    Regards,
    Graham Holden (g-holden AT dircon DOT co DOT uk)
     
    Graham Holden, Mar 17, 2005
    #1
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  2. Graham Holden

    MadHatter Guest

    I've got a 25, which is sometimes a bit too much. the set you're
    looking at will give you a bit more flexibility. I may have to get a
    shorter one in the future.

    It's allowed me to get very close to subjects. I was taking pictures
    today, and I bumped the lens hood into something maybe four inches
    away.

    My camera meters fine with the tube.

    I've used mine with my 50mm and 25-135mm lenses. I haven't tried it
    with any longer focal lengths.
     
    MadHatter, Mar 18, 2005
    #2
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  3. Graham Holden

    DoN. Nichols Guest

    O.K. The 50mm f1.8 is a simple lens (e.g. neither a telephoto
    or a wide-angle), so its behavior is fairly predictable.

    It is 50mm focal length, so with an additional 50mm of
    separation between the film and the lens, it should get down to a 1:1
    ratio -- that is, the image is the same size as the object. At this
    extension, the focus adjustment on the lens is pretty useless -- you have
    to focus by moving the camera/lens combination towards/away from the
    object.

    So -- your 36mm spacer, plus the 12mm one will get you to 48mm
    extension, and your lens focus adjustment should cover the extra 2mm, so
    you can get the 1:1 ratio.

    However, the 50mm f1.8 is not optimized for work this close, so
    you will probably need to stop it way down. Macro lenses designed for
    this are more often around f3.5 maximum aperture, IIRC.

    And to go beyond this, with your normal lens, you will need a
    way to reverse the lens so the front is pointing towards the camera and
    sensor, as the image is now larger than the object. In earlier cameras
    (without autofocus), such reversing rings were available. If you can
    find one, you will be totally disconnected from your autofocus and your
    metering (as there is no provision for routing the CPU contacts to the
    other side, even if your extension tubes couple them through.) So --
    you will be in the position of taking trial exposures, examining the
    histogram display, and adjusting exposure until you get it right. I
    hope that what you photograph doesn't have functional wings or legs. :)

    Note that the "28-105mm f3.5-4.5D" lens has a macro mode which
    is quite good -- except that at maximum close-up, it tends to shadow
    part of the image from illumination from the built-in flash.

    When *I* want to take extreme close-ups with the D70, I use my
    ancient Medical Nikkor, which has a built-in ring flash, and a built-in
    exposure computer (mechanical linkages), so I use the camera in manual
    mode. You need the proper flash adaptor to handle the higher voltage
    connection from the antique flash. You will see the recommended one in
    the manual as a footnote to the list of lenses which can work with the
    camera. This presumes that you can find a Medical Nikkor these days.
    Mine was quite old and well used (and well cared for) when I got it at a
    swap meet.

    The two problem are:

    1) Past a certain magnification ratio, there is too much light
    for the lowest ISO that the D70 offers -- though a neutral
    density filter might make the difference, stacked with the
    supplied close-up lenses used on that lens.)

    2) The annotation in which the lens prints the magnification ratio,
    or a frame number on the image is lost -- as it prints in the
    corner, past where the D70's sensor stops. You've still got
    frame number annotation, but not the magnification ratio, unless
    you edit into the "comments" feature.
    It will let you get closer to the subject than the normal
    focusing range. I'm not sure how well I can calculate that with a zoom,
    which is playing all kinds of optical tricks, and which (I think) is
    holding a back focal length pretty constant. Telephotos (in contrast to
    plain long lenses) have a negative lens as part of the assembly, so the
    lens can be closer to the film (sensor) than would otherwise be
    possible, and (extreme) wide angle lenses are sort of a backwards
    telephoto lens, so in either case, what focal length is marked may bear
    little resemblance to how the extension tubes will work with the lens.

    The way to find out is to add the shortest extension tube, mount
    the lens, and move towards the object while looking through the
    viewfinder until things come into focus. Repeat the experiment with the
    other individual tubes, and with them in combination.
    *If* the metering will work at all through the tubes. It
    certainly won't with my old set, nor with my bellows. Both of those
    lack the contacts to allow the lens to communicate information to the
    camera body. What you have found appears to have that feature, though
    with the exclusion of the 'S' series lens, and the lack of the 'D'
    information, maybe not. (Or maybe only some of the CPU contacts are
    brought through, not all of them.) If you can test them in the photo
    shop, do so -- bring all the lenses which you consider it important to
    test with the extension tubes, (probably something in the 45-55mm range
    would be best.) See what it does, and bring some reasonable test
    subject.
    Get a tabletop tripod. I think that you'll be in a position
    where you will need to repeat test shots until the histogram confirms a
    good exposure. And pray for stationary subjects.

    Note that since focusing at the 1:1 ratio involves moving the
    camera/lens combination, sometimes having a focusing rack to which the
    camera is mounted before you get to the tripod will help. Good bellows
    setups often had a second set of rails to allow you to move the
    combination for such close focusing. But I don't think that there are
    any bellows setups which couple through the AF mechanism and the CPU
    connections, so you go fully manual for this.

    I hope that this helps,
    DoN.
     
    DoN. Nichols, Mar 18, 2005
    #3
  4. Thanks very much (and to "MadHatter") for your reply.

    On 18 Mar 2005 00:17:26 -0500, (DoN. Nichols) wrote:

    I think it's limited contacts; one description (e.g.
    http://www.londoncamera.co.uk/catalog/product_info.php?products_id=1664)
    says "D" information is not sent because the lens is focusing closer than
    it thinks it can (which I read as "it could be sent, but would be of no
    use, so we don't"), and that while it normally allows auto-focus, this
    won't work with silent wave (AF-S) lenses, presumably because the contacts
    for the lens' motor are missing.

    Thanks again for your advice.


    Regards,
    Graham Holden (g-holden AT dircon DOT co DOT uk)
     
    Graham Holden, Mar 18, 2005
    #4
  5. Graham Holden

    Crownfield Guest

    is that the same as a dumb chip lens?
    why would that happen unless the design is off.
     
    Crownfield, Mar 18, 2005
    #5
  6. I'm not 100% sure which bit you're asking about, so sorry if I'm answering
    the wrong bit:

    "Ordinary" auto-focus lenses ("AF" something) are focused by a motor in the
    camera body driving a _mechanical_ link to the lens.

    Nikon also produce a range of "AF-S" lens where the motor is inside the
    lens itself, and there is an _electrical_ link from the body to control
    focusing.

    My reading of the above page is that the Kenko extension rings provide the
    mechanical coupling for "normal" auto-focus lenses, but not the [newer]
    electrical coupling for AF-S lenses.



    Regards,
    Graham Holden (g-holden AT dircon DOT co DOT uk)
     
    Graham Holden, Mar 18, 2005
    #6
  7. I currently own a set of the Kenko tubes which I occasionaly use with a
    50mm, and the tubes do have both the mechanical and electrical links. I
    checked with my 18-70DX, and the D70 does focus through the tubes. It tends
    to seek a lot though, so I generally focus manually anyways.

    I find that automatic focus with a non-S lens (like the 50mm) uses up the
    battery a bit faster, especially if you stack multiple tube sections. I get
    the impression the in-camera focus motor works a lot harder to drive the
    lens through the tube sections.
     
    Richard Hempsey, Mar 18, 2005
    #7
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