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Thread: time conversion

  1. #1 time conversion 
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    Hi there
    By my own admission I'm not good at maths and need some help in converting something. Basically I'm using Audacity (sound recording software) to check the time that a camera shutter is open, to check the accuracy of cameras. Audacity provides the time in a decimal format eg 0.010 seconds. I need to convert that to fractions of a second eg 1/100th of a second in this case. The example I've given you is correct but I can't work out how you do this. Any help would be much appreciated. Thanks, Julian


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  3. #2  
    Brassica oleracea Strange's Avatar
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    You can use a computer to do the work for you, for example: rationalize 0.765 - Wolfram|Alpha


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  4. #3  
    Genius Duck Dywyddyr's Avatar
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    Quote Originally Posted by tawnyman View Post
    0.010 seconds. I need to convert that to fractions of a second eg 1/100th of a second
    How much do you have to multiply by to get rid of the decimal places?
    To use your example 0.01 - multiply by 10 = 0.1 seconds, another 10 = 1 second. Therefore it's 1/(10 x 10) = 1/100.

    Or Strange's example 0.765 is, similarly, 765/(10 x 10 x 10) = 765/1000. Which is 153/200.
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  5. #4  
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    That's great. Now, shutter speeds are always expressed as 1/ number so how would I go about converting, in your example, 153/200 to 1/ number? I'm sure I did this at school but that was nearly 30 years ago now! Thanks, Julian
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  6. #5  
    Genius Duck Dywyddyr's Avatar
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    Quote Originally Posted by tawnyman View Post
    That's great. Now, shutter speeds are always expressed as 1/ number so how would I go about converting, in your example, 153/200 to 1/ number?
    You can't!
    Well you can, but...
    Just divide both values by the numerator (153) = (153/153)/(200/153) = 1/1.3.
    But that doesn't give you what you actually want (in this case) since you're looking for the denominator.
    See below:

    According to Wiki the most common shutter speeds are

    • 1/1000 s 0.001
    • 1/500 s 0.002
    • 1/250 s 0.004
    • 1/125 s 0.008
    • 1/60 s 0.0166
    • 1/30 s 0.0333
    • 1/15 s 0.0666
    • 1/8 s 0.125
    • 1/4 s 0.25
    • 1/2 s 0.5
    • 1 s 1

    so in this case you'd be looking to change 153/200 into the closest of those values.
    Your best bet is to do it the other way round - convert the shutter speed to a decimal value (added in blue), and then look for the closest.
    In the case of 0.765 it's (slightly) closer to 1 than 0.5.
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  7. #6  
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    Thank you, that's very useful. I've now proven that my camera is running slowly, mind you it is 60 years old and probably needs a clean! Julian
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  8. #7  
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    Thanks, Dwywddyr, yes, I had that list to consult but wanted to get a more accurate idea of the speeds that fell between those numbers. I realise now that having 1 on the top of every fraction will give some decidely non-whole numbers on the bottom. I was trying to get my head around 1/1.19th before I realised this!
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  9. #8  
    Genius Duck Dywyddyr's Avatar
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    Glad to have been of some help.
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