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Device to measure FPS


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#1 Roland Morgan

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Posted 18 March 2014 - 01:59 PM

02-254I6101.jpg Hey guys,

 

I'm having trouble identifying something and would just like to know the general reference to this piece of equipment. Any thoughts?


Edited by Roland Morgan, 18 March 2014 - 02:00 PM.

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#2 Glenn Brady

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Posted 18 March 2014 - 04:12 PM

I'm not sure what you mean by ". . . would just like to know the general reference to this piece of equipment."  Guessing you're asking about how the device works, I can say it's intended for use with motion picture cameras having a reflex viewfinder and mirrored shutter.  The LEDs illuminate in sequence, their speed determined by the speed selected (viz, 24, 25, or 30) on the Media Logic device.  When viewed through the reflex viewfinder, the LEDs will appear to stand still when the camera's speed has matched the speed selected on the Media Logic device. 


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#3 Roland Morgan

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Posted 18 March 2014 - 04:43 PM

I'm sorry, let me clarify my question: what is this called? I wanted to be able to find one to purchase, however I am unsure how to name the item in my search.


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#4 Glenn Brady

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Posted 18 March 2014 - 05:04 PM

I think it's called a speed checker.  They appear from time-to-time at eBay; I'm not sure if they're available new.


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#5 Chris Millar

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Posted 18 March 2014 - 05:05 PM

Maybe you're well aware but this sort of stuff is easily made nowadays with cheap microprocessor development boards... If you have no luck try an arduino forum, with a weee bit of experience it's the kinda thing that could be made in 5~10 mins... For *any* FPS a mirror shutter camera can shoot ;)
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#6 Randy J Tomlinson

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Posted 19 March 2014 - 06:27 AM

i used to build such stuff with atmega microprocessors.


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#7 Phil Rhodes

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Posted 19 March 2014 - 07:09 AM

It's easy to do these days, but you need to be a bit careful: for a precision measurement device, the sort of everyday quartz clock crystals that are used on most microcontroller implementations aren't really good enough. They're not good enough for jam sync timecode devices, for instance, which require a drift of perhaps a frame in 24 hours (which is better than 0.2 parts per million in a worst case of 60fps whereas an everyday crystal is probably 100ppm). Temperature-compensated crystal oscillators (TCXOs) are just about good enough - 1.5 to 3ppm - and relatively easy to use.

 

Better than that starts to require things like a temperature-controlled crystal (oven-controlled or OCXO) which can be very slow to start up and power hungry. And then you're on to rubidium frequency sources that take a week to stabilise, draw 5A off the mains and come in a foot-deep, 4U rack case. But that's a proper atomic clock.

 

P


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#8 Chris Millar

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Posted 19 March 2014 - 06:51 PM

By then the frame to frame timing variation would make the precision redundant anyway?

Even the position you held the LED in frame would show up the slight inconsistencies in the shutter blade manufacture/design ? Actually, no - whoops - that'd just appear as phase and duty cycle variation... Which you'd see as a 'speed' change as you moved the LED, but not in the static sense...

Interesting stuff
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