Ye Olde 35mm shutter speed rule of thumb ... digitized

Discussion in 'Digital SLR' started by -hh, Dec 14, 2005.

  1. -hh

    -hh Guest

    We all probably know the traditional rule of thumb for the minimum
    shutter speed on 35mm SLR's, namely 1/(lens focal length in
    millimeters). Thus, we use 1/60sec for a 50mm lens, etc.

    For full frame dSLR's, it is logical that this rule would still apply
    with no changes.

    However, I've recently 'been informed' that this doesn't apply to 1.6x
    dSLR's like the Canon 10D, 20D, dRebel (300D) or dRebel XT (350D).

    So, a multi-part question:

    1. Historically, did the 1/(mm) rule apply to formats other than 35mm
    (For example, 645): did it stay the same, or were there different
    'rules of thumbs' for each format?

    2. Assuming that the 1/(mm) rule does apply to a 1.6x-type dSLR, would
    the applied lens focal length be the actual value, or the "35mm
    equivalent" value?

    For example, a 50mm lens on a dRebel would be ~80mm effective. As
    such, should the minimum shutter speed be 1/60sec or 1/90sec?

    3. If [2's assumption] doesn't apply, what should be the rule of

    FWIW, I know that I'm probably splitting hairs on normal-to-wide
    lenses; my concern is with longer telephotos where a tripod's not an
    option, and each stop tends to get difficult/expensive.

    -hh, Dec 14, 2005
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  2. -hh

    sfarifi Guest

    As the "shake" of the camera increases directly with the focal length
    of the lens (distance travelled at the "other" end is longer - here
    "other" refers to what is being captured), I would say that the only
    thing that matters should be the "effective" focal length of the lens
    being used. So, with a 50mm lens on a 1.6x camera the "hand-holdable"
    shutter speed would be 1/80. The nominal specs of the lens should not

    sfarifi, Dec 14, 2005
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  3. -hh

    phk Guest

    There are a couple of ways to look at this. On the one hand, the
    actual size of the "shake" on the small sensor is identical to the size
    of the "shake" on the larger film. However, to get the same size
    print, the sensor image has to be expanded by 1.6 relative to the film
    image, which expands the shake by 1.6 also. A long way to say that I
    agree with the 1/80 for 50mm with 1.6. A strong case for image
    stabilization when combined with f5 zoom lenses.
    phk, Dec 14, 2005
  4. Since a 120 film photo is being enlarged less than a 35mm one, then to
    get the same degree of camera shake the shutter speed of the roll film
    camera can actually be slower for a given focal length. However, other
    factors are important.

    First, the type of camera matters; SLRs do tend to suffer internal
    movements on taking a photo more than rangefinders; conversely a light
    camera is more susceptible to moving than a heavy one (more inertia).
    The best camera I use for shake is a Mamiya 6 (a heavy rangefinder)
    which can with care give usable results at 1/30 with a 50mm lens.

    Second, the use of the result matters. You can get away with a lot more
    on a photo for printing at 4x6" or for web display than you can on one
    for printing at 12x16". Since the main reason people use 120 film is to
    get ultimate quality, they probably want less camera shake.

    Third, the person's own skill at hand-holding varies a lot. I have known
    people who would need to use 1/4f not 1/f seconds to get a sharp result.
    Personally I try to use 1/2f where I can; though I get usable results at
    1/f, those at 1/2f are sharper under critical examination.
    Given the extra magnification required from an APS-C sized image to get
    a given sized output, then the "35mm equivalent" would be closer to the
    Even for normal-to-wide, there is a cut-off point!

    David Littlewood, Dec 14, 2005
  5. -hh

    -hh Guest

    Thanks for all your comments.

    I did figure that the physical basis for the rule of thumb was that it
    was predicated on the physical geometry of the lens optics...cut the
    subtended angle in half, and a shake moves it twice as far on the
    recording medium, hence the shutter speed needs to double, etc.

    -hh, Dec 15, 2005
  6. -hh

    Royce Guest

    That would be my take, too -- the "effective" focal length of the lens.
    Keep in mind that this old rule of thumb is for you to obtain
    "hand-holdable" shots the "majority" of the time -- presuming you know
    how to properly hold a camera ;-) We SLR shooter usually do, but the
    point-n-shoot people don't usually get the benefits of a "3-point
    holding system" (your two hands - with your elbows braced against your
    body, and with the camera's eye-piece and back braced against your
    cheek, nose and forehead).

    Have you noticed how most of the point-n-shoot people avoid their eye
    level viewfinders like the plague, and instead use their LCD screen in
    real-time video display to view and frame their images? This comes
    from imitating the way most have chosen to shoot their video-cams --
    holding the camera out away from them at arms length as they view their
    LCD displays! In fact, many of the consumer "slimline" digital cameras
    have NO eye-level viewfinders anymore.

    STABILIZATION: Lenses with the stabilization feature will often enable
    you to reduce your shutter speed by a factor of 2 (going from say,
    1/125 to 1/30) and sometimes to a factor of 3 (down to 1/15); but
    REMEMBER: stabilization has no effect on the subject's movement ....a
    little problem I sometimes keep forgetting when I'm photographing
    active children!

    Another method of personal "stabilization" is to use the same
    techniques (in breathing, etc.) that firearm shooters use in
    competition matches. Older photographers could also shut off their
    pace makers momentarily before each shot ;-)

    Royce Bair
    Stock Photographer and Writer/Consultant for
    Epson P-2000 Storage Viewer - How to Upgrade to P-4000 specs
    Royce, Dec 15, 2005
  7. -hh

    Celcius Guest

    Right you are
    They probably do, because the eyepiece / viewfinder is not of good
    quality. With the Canon G1 or the Canon S300 which I used, you couldn't
    use the viewfinder effectively. Then I bought a Canon Pro1. That one
    had a much better viewfinder, as my actual camera now, the Rebel XT.
    Very good point, indeed

    Celcius, Dec 15, 2005
  8. -hh

    zeitgeist Guest

    I think the correlation between the focal length of the lens and a shutter
    speed to hand hold an exposure was merely co-incidental happenstance, a
    clever someone noticed it seemed to be a good rule, but there's no factual
    basis. It is certainly a case of YMMV.

    There are couple variables, the mirror slap being one of them. I don't
    think I would want to hand hold an RB at any shutterspeed, yet it was a
    common practice in early color photography at weddings to shoot at 1/15th at
    wide open with candles for some arty orange blobs, (yeah sure, it would be
    underexposed but you would get 'something' on the neg that was printable and
    for the era that was cool.)

    Mirror slap was usually less of a problem with a 35mm so an extra stop on
    the shutter was theoretically possible.

    OTOH, if you used a tripod more often you'd be surprised at how often your
    images look crisper, sharper, clearer, snappier.

    What if you said, don't hand hold slower than your flash sync. If you had a
    camera that synced at 1/60th the rule would make some sense more often than
    those who camera's synced at 1/250th or 1/30th.

    This reply is echoed to the z-prophoto mailing list at
    zeitgeist, Dec 16, 2005
  9. -hh

    Dave Guest

    You have been misinformed. An increase or decrease in focal length
    will result in an increase or decrease in apparent hand shake
    regardless of format. Try hand holding an 8X10 with normal lens at
    speeds under 1/300th and the consequence will be a blured contact
    print (zero enlargement print). A 50mm wide angle lens on a medium
    format can be held at 1/50th while a 100mm lens on the same format
    will requireat least an 1/100th second shutter speed. I can easily
    hand hold a 24mm lens on my 20d at 1/25th second just like I can the
    same lens on my 35mm EOS RT.
    No. Increasing focal length will magnify hand shake to the same extent
    regardles of format.
    The actual focal of the lens will require the same shutter speed to
    off set hand unsteadiness regardless of how much the image plane is
    The rule of thumb would require at least 1/50th.
    Shutter speed should equel or exceed the lens focal length in
    millimeters reguardless of crop or format.
    You should consider an IS type lens. Also keep in mind that the
    minimum shutter speed rule of thumb is only an approximate. You should
    make carefull tests under your normal shooting conditions. I want to
    take the hand shake factor out of my images so I increase shutter
    speed at least one stop over what the rule of thumb dictates, when
    ever possable.

    East Englewood

    The proof is in the print.
    Dave, Dec 16, 2005
  10. -hh

    -hh Guest

    Ah, so a second opinion shows up.

    Dave, you're therefore not concerned then that the differences in
    recording media (1.6x - 35mm - Medium Format) for any given length lens
    all have geometrically different net subtended angles of view?

    The reason I ask is because I would have figured that it was the total
    geometric angle that was subtended onto the recording media that would
    be what maters.

    For example, let me ask what I think is the same question slightly
    differently worded:

    Suppose I have a 200mm telephoto, so the rule of thumb would say ~1/200
    or faster

    I now put a 2.0x teleconverter on this lens. Since by your arguement
    this would be "merely cropping" the viewed image from the same physical
    piece of glass, it would appear that your suggested rule of thumb
    starting point would ignore the teleconverter (just like it is ignoring
    the 1.6x in the dSLR body), so you'd still say ~1/200, instead of
    changing to ~1/400.

    Is this correct?

    If its not correct, then how is the 1.6x cropping factor from a dSLR
    body to be treatedly differently than from the geometric angle cropping
    from any (1.4x, 2.0x) teleconverter?

    Yes, they're a useful tool. However, since my question is to determine
    a baseline assumption starting point, modifications to said baseline
    (such as IS glass) are at this stage irrelevant.

    That's why its called a 'Rule of Thumb" :)

    Overall, please understand that all I'm really trying to do is to sort
    out the most basic effects of an introduction of a 1.6x crop factor
    into my existing equipment...not all of the refinements that will
    occur, such as IS and technique.

    My baseline assumption was to use '35mm effective equivalent' under the
    logic that its 1.6x geometric effect is pragmatically identical to a
    teleconverter, so it should be treated the same as a teleconverter.
    But your claim is effectively contrary to that by saying that it can
    effectively be summarily ignored...which would also suggest that I can
    ignore teleconverters too. Sorry, but that runs contrary to my
    experience with teleconverters.

    -hh, Dec 16, 2005
  11. -hh

    Paul Mitchum Guest

    A 2x teleconverter sucks two stops out of the available light. You
    *must* lengthen the shutter time to get the same exposure. A 200mm lens
    at 1/200 might be acceptable, but add a 2x TC and you'll get a dark
    frame. Therefore the comparison to a DSLR 1.6x crop factor isn't really

    But to get back to the rule-of-thumb: The issue isn't shake, it's
    sharpness. Minimal shake or mirror slap will fuzz up the sharpness, but
    only for certain *output sizes.* A postage-stamp-sized print won't show
    much shake at all. A 10-foot square blow up will. So the rule of thumb
    applies generally to an average size print, not a sensor or a lens. If
    you're shooting for a huge print, you better have a tripod handy (or a
    whole lot of light), regardless of focal length or format.

    This leads us back to the issue of depth of field. An image with really
    bad camera shake has no depth of field. As shake is minimized, depth of
    field increases to its optical limits.

    The 1/mm rule doesn't mean much. It's just a reminder that you're going
    to need shorter shutter times because longer focal lengths amplify
    Paul Mitchum, Dec 19, 2005
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