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Author Topic: My brain hurts. Anyone good at maths?  (Read 1581 times)

Pete_R

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My brain hurts. Anyone good at maths?
« on: November 03, 2015, 04:46:37 PM »
If I want to express a shutter speed error in terms of stops (or EV), how do I work out the error?

e.g. If a shutter is set for 1/1000 it should be open for 1ms. If it's actually open for 2ms that's +1 stop error. If it's open for 0.5ms that's -1 stop error. I need a spreadsheet formula that calculates this.

Anyone?
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Pete_R

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Re: My brain hurts. Anyone good at maths?
« Reply #1 on: November 03, 2015, 05:31:19 PM »
OK, I think I cracked it. Need to convert each value to EV first then just take one from the other.
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Francois

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Re: My brain hurts. Anyone good at maths?
« Reply #2 on: November 03, 2015, 09:21:34 PM »
calculating ev variation is one way of doing it... and probably the simplest especially when starting with a ms value.

Let me think...

nope... nothing better comes to mind

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Francois

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Jack Johnson

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Re: My brain hurts. Anyone good at maths?
« Reply #3 on: November 04, 2015, 06:39:30 AM »
Convoluted, and there's probably an easier way, but:

=(LOG(B2)-LOG(A2))/LOG(2)

...where column A has the target shutter speed and column B has the actual shutter speed. If you want that in the nearest third of a stop, that's left as an exercise for the reader. ;)
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Pete_R

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Re: My brain hurts. Anyone good at maths?
« Reply #4 on: November 04, 2015, 08:16:30 AM »
Quote from: Jack Johnson on November 04, 2015, 06:39:30 AM
Convoluted, and there's probably an easier way, but:

=(LOG(B2)-LOG(A2))/LOG(2)

...where column A has the target shutter speed and column B has the actual shutter speed. If you want that in the nearest third of a stop, that's left as an exercise for the reader. ;)

That works and would make my spreadsheet less complicated.
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Jack Johnson

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Re: My brain hurts. Anyone good at maths?
« Reply #5 on: November 08, 2015, 04:59:17 PM »
What are you working on?

The guy who CLA'd my Supermatic shutter gave me a handwritten note with the shutter accuracy (which I was extremely surprised by), but I've seen electronics projects to measure shutter speed, and it seems like having an Arduino in an Altoids tin that would spit out shutter accuracy in stops would be darned handy at a garage / boot sale. :)
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Pete_R

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Re: My brain hurts. Anyone good at maths?
« Reply #6 on: November 09, 2015, 09:26:10 PM »
Quote from: Jack Johnson on November 08, 2015, 04:59:17 PM
What are you working on?

Just posted some info over on the Articles board here http://www.filmwasters.com/forum/index.php?topic=8323.0

Quote
The guy who CLA'd my Supermatic shutter gave me a handwritten note with the shutter accuracy (which I was extremely surprised by), but I've seen electronics projects to measure shutter speed, and it seems like having an Arduino in an Altoids tin that would spit out shutter accuracy in stops would be darned handy at a garage / boot sale. :)

What I have is probably close to a "Arduino in an Altoids tin" but I don't think it would be usable in the field.
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