# Verifying DSLR shutter speeds



## 480sparky (Apr 14, 2012)

Other than checking the exif data and assuming it's correct (i,e, 1/100 sec is truly 0.01 sec.), does anyone have a method of actually _measuring _the shutter speed of a DSLR?


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## minooo (Apr 14, 2012)

maybe comparing the exposed image with a similar camera at the same settings.
Or, if you know how to expose manually, I mean like you did on a mechanical camera... then do so and see if the picture came right.


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## Tony S (Apr 14, 2012)

I tried it once with a yard stick....... but it ruined the shot when I couldn't get the lens on.


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## Garbz (Apr 14, 2012)

Shoot something that is moving at a known pace and measure? 

The trick to test cameras back in the day was vary the shutter speed over the aperture. If the shots were not consistently bright you've either got a sticking shutter or a sticking aperture blade. To what end do you want to measure it? 

The scientific method would be to record the sound your camera makes. High gain and at a very high sample rate. We use a system like this at work to measure precisely when valves on a compressor are opening and closing with an ultrasonic probe. The other way I've seen it done is using a sensitive accelerometer mounted to the camera. The results are usually one huge spike (mirror slapping up), two smaller ones (shutter opening and closing) and one huge one to finish (mirror returning).


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## 480sparky (Apr 14, 2012)




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## Garbz (Apr 15, 2012)

Again, why? Is your camera producing inconsistent or widely varying exposures? Send it in. If not you don't have a problem. If you're doing science then you shouldn't be using a DSLR anyway, there's specialised cameras for you to buy there.


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## Helen B (Apr 15, 2012)

Folks who don't have an old shutter speed tester could use the mic input on their PC with a photocell. The mic input is a high impedance voltage driven ADC, so it can be used to measure any (small) voltage, such as that across a phototransistor. Because the mic input is most likely to have a small bias voltage across it so that it can power electret mics you may be able to connect the phototransistor directly across the mic input with no other circuitry being necessary, if not you can use the USB voltage. In the past I have found a sound board's clock to be accurate to about 5 ppm at worst - good enough for shutter testing.

I would expect the main error in the system to be the tuning of the shutter blade position with respect to the signal - I would expect that measured speed would often be longer than the actual speed. This is because the exact blade position at which the meter responds is not known. You might want to use a laser, possibly attenuated, so that the response is more precise.


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## 480sparky (Apr 15, 2012)

Garbz said:


> Again, why? Is your camera producing inconsistent or widely varying exposures?



Ever hear of _Predictive Maintenance_?.  Not _Preventative Maintenance_, like changing your motor oil regularly.  Predictive, as in knowing a given shutter speed is slowly over- or under-exposing.  Ever check your tire's air pressure?




Garbz said:


> Send it in.



If a problem is known, it's easily corrected in the field.  No need to.




Garbz said:


> If not you don't have a problem.



And how do you know you do or don't?  An error may not be so obvious when you're shooting a wide variety of subjects, using a different shutter speed every actuation.




Garbz said:


> If you're doing science then you shouldn't be using a DSLR anyway, there's specialised cameras for you to buy there.



I can give you my PayPal account email.  You can send me the funds to purchase these specialized cameras.  Or you can send me a bank check or money order.  Makes no difference to me, it's your money.


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## 480sparky (Apr 15, 2012)

Helen B said:


> ........I would expect the main error in the system to be the tuning of the shutter blade position with respect to the signal - I would expect that measured speed would often be longer than the actual speed. This is because the exact blade position at which the meter responds is not known. You might want to use a laser, possibly attenuated, so that the response is more precise.



The photocell is in the rear of a small brass tube.... so literally it has it's own 'lens hood'. So it's not 'seeing' the entire sensor.  I've considered a laser, but simply used the modeling lamp in my monolight to test the theory.


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## Garbz (Apr 16, 2012)

480sparky said:


> Ever hear of _Predictive Maintenance_?.  Not _Preventative Maintenance_, like changing your motor oil regularly.  Predictive, as in knowing a given shutter speed is slowly over- or under-exposing.  Ever check your tire's air pressure?



Electrical reliability engineer is my day job. I live and breath predictive maintenance. I've just never heard anyone do it on consumer gear 



480sparky said:


> And how do you know you do or don't?  An error may not be so obvious when you're shooting a wide variety of subjects, using a different shutter speed every actuation.



Using the method I was talking about. Pick a stable subject in a stable lighting condition and fire off shots altering the aperture. This will expose errors relative to shutter speeds or aperture blades and if you have a problem investigate further. 
A lot of people concern themselves with absolute values. Personally I couldn't care less if my shutter speed is 3 times slower than it's supposed to be, providing it is repeatable, works consistently, and the camera meter has taken the speed into account (maybe via a factory calibration, or my own setting in the menu). Any deviation would then be shown by the test above. 

Predictive maintenance is used to find out when a device will fail. It is used on devices that fail during the normal course of use. i.e. Transformer oil. You want to monitor the oil moisture because you know it has a limited lifetime after which it will cause catastrophic failure, or motor vibrations because motor bearings do not last indefinitely and you want to know when it is most economical to overhaul it. 

DSLRs don't have an economical time to replace a shutter. The vast majority of DSLRs will be sent to some Chinese electronic scrap yard with perfectly working shutters. It is fully expected that the camera will not fail in the time you own it and as such predictive maintenance stops being worth the time taken to perform. Shutter failures are rarer than you think and unless you long term trend your camera you're not going to get any useful data out of it.


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