# Thread: time conversion

1. 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

2.

3. You can use a computer to do the work for you, for example: rationalize 0.765 - Wolfram|Alpha

4. Originally Posted by tawnyman
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.

5. 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

6. Originally Posted by tawnyman
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.

7. 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

8. 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!

9. Glad to have been of some help.

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