Speeds

Discussion in 'UK Photography' started by D.M. Procida, Sep 22, 2012.

  1. D.M. Procida

    D.M. Procida Guest

    In exposure control, everything can be conveniently managed by doubling
    or halving values - film speed, aperture, shutter speed.

    Even the most basic mathematician would notice though that the sequence
    of marked shutter speeds on most cameras:

    15 30 60 125 250 500 1000 2000

    isn't a doubling.

    Are the actual shutter speeds exactly the same as the marked ones, or
    close enough, or do the actual ones follow a precise sequence.

    Daniele
     
    D.M. Procida, Sep 22, 2012
    #1
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  2. D.M. Procida

    Rob Morley Guest

    On Sat, 22 Sep 2012 10:36:18 +0100
    With most mechanical cameras the shutter speed will vary from what it's
    supposed to be, but not by enough to cause problems with most films. As
    a camera gets older its shutter speeds will generally get slower - dried
    up lube and tired springs, possibly a bit of corrosion. If you're
    using colour transparency film you'll notice less than half a stop
    difference in exposure, b&w negs won't mind.
     
    Rob Morley, Sep 22, 2012
    #2
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  3. D.M. Procida

    Bruce Guest


    The shutter speeds are nowhere near as accurate as the precision of
    the engraving on the shutter speed dial might lead you to think.

    I still have a shutter speed checker which records the effective
    shutter speed in milliseconds and decimals thereof. 1/1000 sec is
    1.00 ms. 1/125 sec is 8 ms. It would seem logical to look at 1/60
    sec as 16 ms and 1/30 as 32 ms, even though the products of these are
    not 1000.

    Most cameras get within 20% of the correct speed. Ironically, one of
    the most problematic brands is Leica, whose 1/1000 sec fastest speed
    on any model from M3 through M1 to M7 and MP is likely to be nearer to
    1/700 sec, or 1.4 ms rather than 1.00. A newly serviced Leica M1 to
    MP might manage something closer to 1/1000 sec, but not much closer.
     
    Bruce, Sep 22, 2012
    #3
  4. D.M. Procida

    Woody Guest

    You need to understand a bit more about exposure, then it will
    make sense.

    Consider how film takes a picture in a water scenario. The film
    equates to a bucket and needs a fixed quantity of water to fill
    it, or in film terms a fixed quantity of light to expose it
    correctly. In water terms the size of the bucket is fixed - this
    the the film speed. The faster the film the smaller the bucket.

    You are now going to fill the bucket from a hosepipe. The large
    the diameter of the hose (the lens aperture) the quicker the
    bucket will fill and vice versa. Therefore double the area of the
    hose outlet and you will only need the water on for only half the
    time.

    The f-number on the lens aperture is the ratio of the diameter of
    the iris when it is shut down to the focal length of the lens.
    However the area of a (nominal) circle is related to the square
    of the radius, so for the aperture to change area by a factor of
    2 the radius must change by a factor of the square root of 2,
    i.e. 0.7 if going down or 1.4 going up. To put it another way if
    you change the aperture by two stops the f-number will double or
    halve accordingly.

    Hence you have apertures (in 'normal' steps) of 2, 2.8, 4, 5.6,
    8, 11, 16, 22 which are all changes by a factor roughly
    equivalent to the square root of 2.

    If instead of changing the size of the hose you do it by changing
    the duration, then the change in time is a simple factor of 2.
    Hence the shutter speed steps that you have quoted. The fact that
    there is a minor change of multiplication factor between 60 and
    125 is academic, it is near enough to be insignificant.

    This description equally applies to digital cameras as it does to
    film. However certainly for digital cameras, and for most
    electronically controlled film cameras made since about 1990, the
    camera can make a metering decision and set the aperture or speed
    steplessly. You might have an aperture of 5.9 (although in
    reality cameras often go in half-stop steps even though they
    could do otherwise) or a shutter speed of 1/168 of a second.
    Digital cameras record something known as the EXIF information
    with the picture - this info contains all the details of the
    picture, i.e. time and date taken, focal length of the lens in
    use, aperture, shutter time, and some other. If you use something
    like Fastone Image Viewer, a right click on the dark band at the
    right of the picture will show you all of these details.

    I hope that makes sense?
     
    Woody, Sep 22, 2012
    #4
  5. D.M. Procida

    D.M. Procida Guest

    Thanks for taking the time to offer the explanation, though the thing I
    was asking about was simply the:
    (which as you and others have pointed out, is quite satisfyingly a
    mechanical approximation of a theoretical ideal).

    Daniele
     
    D.M. Procida, Sep 22, 2012
    #5
  6. D.M. Procida

    Bruce Guest


    You're welcome.
     
    Bruce, Sep 23, 2012
    #6
  7. D.M. Procida

    Rob Morley Guest

    <snip irrelevant stuff>

    I'm sure he understands how exposure works - the question was about the
    accuracy of quoted shutter speeds.
     
    Rob Morley, Sep 23, 2012
    #7
  8. D.M. Procida

    D.M. Procida Guest

    Maybe, but if someone takes the time to explain something politely on
    Usenet, then good for them. And perhaps someone else will find it
    useful.

    The last thing we want is for people to be discouraged from being
    helpful and polite on Usenet.

    Daniele
     
    D.M. Procida, Sep 23, 2012
    #8
  9. D.M. Procida

    Rob Morley Guest

    Maybe, but if someone takes the time to explain something politely on
    Usenet, then good for them. And perhaps someone else will find it
    useful.

    The last thing we want is for people to be discouraged from being
    helpful and polite on Usenet.[/QUOTE]

    You're right, of course, I should have offered him a cup of tea before
    moaning about his post. And maybe gingernut too.
     
    Rob Morley, Sep 23, 2012
    #9
  10. D.M. Procida

    Bruce Guest


    The most discouraging thing about being helpful and polite on Usenet
    is not to be thanked for your efforts. (HINT)

    You're welcome.
     
    Bruce, Sep 23, 2012
    #10
  11. I used to notice in those camera reviews that actually bothered to test the
    shutter speeds that 1/1000 often fell far short of the claimed speed, and
    in fact there tended to be a progressive fall off of all the faster speeds
    with some cameras. It seems that just as it's best to avoid the biggest and
    smallest apertures on a lens it's also best to avoid the fastest and
    slowest shutter speeds on a camera if you can.
     
    Gordon Freeman, Sep 24, 2012
    #11
  12. D.M. Procida

    Bruce Guest


    Yes, that's a very good point, but I have never seen this problem with
    Nikon equipment. The shutter of my F801s was as accurate at its top
    speed of 1/8000 sec as my Leica M7 was at 1/500 sec, both being around
    15% slow.
     
    Bruce, Sep 24, 2012
    #12
  13. D.M. Procida

    D.M. Procida Guest

    I guess I could record my shutter on my computer, then look at the
    waveform, and using that get an idea of how long it's staying open. But
    that would only work for a focal-plane shutter for the slower speeds.

    Daniele
     
    D.M. Procida, Sep 24, 2012
    #13
  14. D.M. Procida

    Darkside Guest

    juice.co.uk>, D.M. Procida <real-not-anti-spam-address@apple-
    juice.co.uk> writes
    Usenet isn't what it used to be... grumble...
     
    Darkside, Sep 24, 2012
    #14
  15. On Mon, 24 Sep 2012 10:40:49 +0100,
    Google "shutter time tester"
    Fwiw, there's a guy in Romania, an occasional poster to a lens group,
    who makes and sells them for a very reasonable price. I'll have a look
    to see if he's still doing them.
     
    Grimly Curmudgeon, Sep 24, 2012
    #15
  16. D.M. Procida

    Geoff Berrow Guest

    Useful to me. My stepdaughter (doing photography at Uni) asked me why
    f numbers were so strange. I'd taken them for granted for so many
    years it hadn't occurred to me to find out how they were derived. I
    had meant to google it and you saved me the bother. :)





    Geoff Berrow
    www.slipperyhill.co.uk
    New CD, 'Gathering Speed' out now! Available
    on our website or from iTunes/Amazon
     
    Geoff Berrow, Oct 21, 2012
    #16
  17. D.M. Procida

    Vic Guest

    I would have thought this would be one of the first principles of optics
    that photogaphy students should be taught. Michael Langford's textbooks
    "Basic Photography" and "Advanced Photography" used to be (and still should
    be) the staple diet of anyone taking photography seriously. Maybe some parts
    concerned with the chemisty of film can now be omitted, but the laws of
    physics and optics do not change.



    --- news://freenews.netfront.net/ - complaints: ---
     
    Vic, Oct 22, 2012
    #17
  18. D.M. Procida

    Geoff Berrow Guest

    Yeah, you'd think so, but even though she's done two years of
    photography at college and left with Distinctions and Distinction*s,
    her technical knowledge is still very poor.


    Geoff Berrow
    www.slipperyhill.co.uk
    New CD, 'Gathering Speed' out now! Available
    on our website or from iTunes/Amazon
     
    Geoff Berrow, Oct 24, 2012
    #18
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