Pentax SMC-A lens

Discussion in 'Pentax' started by Denny B, Jun 19, 2006.

  1. Denny B

    Denny B Guest

    What is the difference between a SMC Pentax-A lens
    and a SMC Pentax (no-A) lens? I was checking my Pentax lenses
    today and these are the markings on the lenses.

    Can these lenses be used on a *ist Digital
    body and work equally well?
    Will all the lightmeter functions work?

    Thanks
    Denny B
     
    Denny B, Jun 19, 2006
    #1
    1. Advertisements

  2. Denny B

    m II Guest


    This site is a good reference.

    http://kmp.bdimitrov.de/lenses/


    All Pentax lenses, K mount or threaded (with adapter) will work on an
    *ist. The degree of functionality varies, however. With an old manual
    thread mount, I have to set the aperture manually. What a chore. Then I
    I have to press the green button in order to have the camera set the
    exposure time. The amount of work involved is obviously backbreaking.

    Well, not really. The fact that the *ist series IS so backwards
    compatible was the deciding factor in my purchasing a 'D' when it
    arrived. It's a really well made camera and I will be supplementing it
    with the new stabilized sensor model when it arrives. It will be handy
    for those longer lenses which I can't seem to hold quite as steady as I
    used to.


    mike
     
    m II, Jun 19, 2006
    #2
    1. Advertisements

  3. : What is the difference between a SMC Pentax-A lens
    : and a SMC Pentax (no-A) lens? I was checking my Pentax lenses
    : today and these are the markings on the lenses.

    : Can these lenses be used on a *ist Digital
    : body and work equally well?
    : Will all the lightmeter functions work?

    The main difference between the two is that a lens with either no manual
    aperture ring or one with an additional setting of "A" can be set to the
    apropriate f-stop electro-mechanically by the camera electronics. If no
    such "A" setting is available you will have to set the f-stop manually and
    then set the camera to match for the meter to work properly. And some of
    the auto functions may be limited or restricted in this setup.

    If your old lens has the "A" setting for the f-stop ring (or no ring) you
    are fine, even if the model number does not specifically have an "A" in
    the name.

    Randy

    ==========
    Randy Berbaum
    Champaign, IL
     
    Randy Berbaum, Jun 19, 2006
    #3
  4. Denny B

    Denny B Guest

    Thank you for your reply if I understand this correctly
    using an "A" lens you set the lens to "A" and the camera
    can set the aperture and shutter speed. If you use non "A"
    lenses you select the f stop and the camera selects the
    shutter speed. My lenses are all K mount.

    Denny B
     
    Denny B, Jun 19, 2006
    #4
  5. Denny B

    Jeremy Guest

    What exactly are you referring to when you say "no-A lens?" If the lens
    says SMC Pentax it could have been the original K-Mount series, which was
    introduced in 1975, when Asahi Optical (Pentax's former name) abandoned the
    M42 screw mount. The next series of lenses was the "M" which came out when
    Pentax introduced a line of smaller SLRs to compete with the Olympus OM-1.
    The M lenses were smaller than the original K-Mount lenses, to be
    size-compatible with the new smaller SLRs.

    Then Pentax came out with a series of program-mode bodies, whose major
    improvement over the older models was that the camera could be operated in
    several automatic modes and the camera's computer could set the shutter
    speed and the lens aperture automatically. Pentax had tried this before
    with the ES and the ES-II (screw-mount cameras). They had 2 major
    drawbacks:

    1: The camera could adjust only the shutter speed, not the lens aperture
    ("aperture-priority"). Depending upon the subject, and whether it was
    moving, that sometimes resulted in shutter speeds that were too low,
    especially if the subject moved from bright areas into the shadows.

    2: Users could set their cameras to manual mode, but that resulted in the
    meter turning off. If you wanted to set your own shutter speed and
    aperture, you needed a handheld meter. Also there were only about 6 shutter
    speeds you could select from. Bummer.

    With the program-mode cameras, Pentax did it right. They created the "A"
    ("automatic") series of lenses with the necessary couplings to allow the
    camera to set the lens aperture, when used in the appropriate mode. They
    also made some changes to the lens' internal mechanics, to ensure that the
    camera could adjust the aperture in an extremely short period of time. And
    they also tweaked the optical formulae of the lenses. The 50mm f/1.7 SMC A
    lens was reputed to be one of the sharpest lenses that Pentax ever produced.
    Finally they made some improvements to the multi-coating formula over the
    previous generations of lenses. I do not know any details about exactly
    what the improvements were.

    The "A" series of lenses were of excellent optical quality, although many of
    us were somewhat disappointed with their build quality. If you compare them
    with the SMC Takumars, the differences were obvious. Aircraft aluminum
    barrels, smooth-as-silk focusing rings, smooth-clicking aperture stops. The
    later SMC Takumars had rubberized focusing rings, but they were of much
    better quality than the rubber rings on the "A" series.

    In fairness to the "A" series, Pentax tried to make as many of them as
    possible in the 49mm filter size, to maximize the ability to use a single
    set of filters on a broad range of lenses. The original K-Mount lenses
    adopted the 52mm filter size, and Pentax users that had an existing stock of
    49mm filters had to either do without filters or buy the new sizes.

    If you want to look at the cameras that the A lenses were designed to work
    with, look at the P-3, P-30, P-30t, P3n, Super-A, and P-50, among others.

    I do not have any Pentax digital gear, so I cannot give you any first-hand
    experience, but I have read that trying to use legacy lenses on modern
    autofocus digital bodies is a real pain in the butt. These lenses may be
    all right as a stopgap measure while you are acquiring your autofocus
    lenses, but their long-term use is of dubious value, because they slow you
    down in ways that seem incompatible with the digital photographic style.
     
    Jeremy, Jun 19, 2006
    #5
  6. Denny B

    Pete D Guest

    Actually on the Pentax D-SLR cameras the A lenses are great and fast you
    just have to manual focus, with the M lenses you simply have to press one
    button to meter then manual focus, pretty trivial really and they are as
    sharp as a tack.
     
    Pete D, Jun 19, 2006
    #6
  7. : Thank you for your reply if I understand this correctly
    : using an "A" lens you set the lens to "A" and the camera
    : can set the aperture and shutter speed. If you use non "A"
    : lenses you select the f stop and the camera selects the
    : shutter speed. My lenses are all K mount.

    Correct.

    Randy

    ==========
    Randy Berbaum
    Champaign, IL
     
    Randy Berbaum, Jun 20, 2006
    #7
  8. : > I do not have any Pentax digital gear, so I cannot give you any
    : > first-hand experience, but I have read that trying to use legacy
    : > lenses on modern autofocus digital bodies is a real pain in the butt.
    : > These lenses may be all right as a stopgap measure while you are
    : > acquiring your autofocus lenses, but their long-term use is of
    : > dubious value, because they slow you down in ways that seem
    : > incompatible with the digital photographic style.

    : Actually on the Pentax D-SLR cameras the A lenses are great and fast you
    : just have to manual focus, with the M lenses you simply have to press one
    : button to meter then manual focus, pretty trivial really and they are as
    : sharp as a tack.

    The "A" or not "A" lenses have nothing to do with the auto focus. The "A"
    denotes a lens that the camera can adjust the aperture automatically. The
    designation that denotes auto focus vs not auto focus is in the "mount". A
    straight "K" mount does not have the tab for the autofocus. But a "K-AF",
    or sometimes written "KAF"' mount does. So a lens that is a K mount with
    no A setting on the manual aperture ring will not be able to automatically
    set the f-stop (or note the f-stop in the exif) and will not be able to
    auto focus. But if the lens has a K-AF mount and either has no manual
    f-stop ring or has a position marked A (normally just past f-22) then the
    camera will have full function. Either lens will be useable on the *ist-D
    and later bodys. But with each function not available there will be
    appropriate restrictions in auto and mode functions.

    I have several Pentax lenses from the early 70's that are manual
    everything that work just fine on my *ist-DS but due to their no auto
    anything my camera is restricted to mostly the very basic functions. I
    have since replaced most of my lens selection (over a long time for fund
    gathering) and love the difference the K-AF "A" lenses make. :)

    Randy

    ==========
    Randy Berbaum
    Champaign, IL
     
    Randy Berbaum, Jun 20, 2006
    #8
  9. Denny B

    Denny B Guest

    Thank you all for your generous
    and adequate replies.

    Thanks kindly
    Denny B
     
    Denny B, Jun 21, 2006
    #9
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.