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09-04-2019, 11:40 PM   #1
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margin of error for shutter speed?

Does anyone know what the margin of error is for the standard K-5's shutter speed? I'm doing an experiment about how the amount of light in a photo is influenced by the amount of time the shutter was open, and I need some error bars. I assume it's the same for every speed value because it would depend on the processor speed. (I doubt it matters, but just in case, the resulting photos are 4928*3264 pixels.)

09-04-2019, 11:49 PM   #2
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Welcome to the forums

I can't help with the information you need, but just for clarification, are you looking for the inconsistency in repeated shots at the same shutter speed - e.g. 1/400s might be 1/394s, 1/408s, 1/402s etc.? If so, my guess is any slight inconsistency (and I'd expect it to be very slight) would be more to do with the electro-mechanical aspects of the shutter assembly than the camera's processing speed. Furthermore, I'd expect it to have far less influence than fluctuations in metering (if used) and any light source(s)...
09-04-2019, 11:52 PM   #3
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Modern shutters should be extremely accurate- or at the very least consistent between the different settings that are available, since the camera is capable of calculating and compensating for any error that might initially exist. I came across this thread which sheds a little bit of light on the matter (but unfortunately doesn't answer your question directly):
Shutter Speed Accuracy... | Amateur Photographer

One big thing to watch out for is that metering systems these days are stepless, so if you want to lock in an exact shutter speed, you should use M mode.

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09-05-2019, 12:50 AM   #4
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As noted above, shutter speeds should be both accurate and consistent when used in manual. The processor will be counting it's clock cycles and the only variation will be the mechanics of the shutter mechanism (which are likely to cancel each other out).

Even back in the 80s electro-mechanical shutters were very accurate. I have an LX test where they were well within a few percent, even though the mechanical speeds from 1/75th upwards were slightly less accurate.

In the precise measurement of light in an image, slight differences in transmission through lenses (i.e. accuracy of aperture positioning) is much more likely to vary. As is the actual brightness of the subject.

09-05-2019, 03:57 AM   #5
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QuoteOriginally posted by rekkandevar Quote
Does anyone know what the margin of error is for the standard K-5's shutter speed? I'm doing an experiment about how the amount of light in a photo is influenced by the amount of time the shutter was open, and I need some error bars. I assume it's the same for every speed value because it would depend on the processor speed.
I have a Calumet sensor that can measure actual shutter speeds in 35mm focal plane (and leaf) shutters. When focal plane shutters went from horizontal travel cloth types to vertical titanium metal alloy guillotine types, the accuracy improved. My exposure time reading device has an accuracy scale of zero error, +/- 1/6 EV and +/- 1/3 EV. As it measures down to tens of thousandths of a second, I have never seen a perfect shutter and the margin of error usually varies at different speeds. The faster shutter speeds have a smaller margin for error and therefore actually have a greater margin of error (percentage wise).

Also note that stated shutter settings are also rounded numbers. Although the camera shows "whole EVs" as 30", 15", 8", 4", 2", 1", 1/2", 1/4", 1/8", 1/15", 1/30", 1/60", 1/125", 1/250", 1/500", 1/1000", 1/2000", 1/4000", in reality it is giving you 32", 16", 8", 4", 2", 1", 1/2", 1/4", 1/8", 1/16", 1/32", 1/64", 1/128", 1/256", 1/512", 1/1024", 1/2048", 1/4096".

When testing shutter speeds, I usually either shoot with the lens aperture wide open or with no lens at all and the mirror up to eliminate the aperture closing to affect the test.

Also for high shutter speeds, you want to make sure you're using a continuous light source such as the sun or tungsten.

Last, you may want to research if digital sensors have "reciprocity failure" like film does as that may be another factor that could effect your measurements.

Last edited by Alex645; 09-05-2019 at 10:18 AM.
09-05-2019, 06:55 AM - 2 Likes   #6
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QuoteOriginally posted by Alex645 Quote
Last, you may want to research if digital sensors have "reciprocity failure" like film does as that may be another factor that could effect your measurements.
If properly designed, they shouldn't - the CCD just counts arriving photons. There is, however, significant non-linear scaling in DSLR camera software.

QuoteOriginally posted by Alex645 Quote
Also note that stated shutter settings are also rounded numbers. Although the camera shows "whole EVs" as 30", 15", 8", 4", 2", 1", 1/2", 1/4", 1/8", 1/15", 1/30", 1/60", 1/125", 1/250", 1/500", 1/1000", 1/2000", 1/4000", in reality it is giving you 32", 16", 8", 4", 2", 1", 1/2", 1/4", 1/8", 1/16", 1/32", 1/64", 1/128", 1/256", 1/512", 1/1024", 1/2048", 1/4096".
For more on this, see my actual measurements: True Shutter Speeds compared to Nominal Shutter Speeds - Actual Measurements - PentaxForums.com

I have made a lot more measurements since with a better LED array (256 LEDs; need to make a big report one of these days!). For all cameras measured (Canon G15 and low-end DSLR (from a friend - don't remember the model number) and Pentax Q7, K3, and K1), the shutter speeds are exceedingly accurate - much less than 1% error, except for the Pentax DSLRs which have a very systematic error when used in the 1/3 shutter speed step mode. In this case, the standard values (such as 1/8 second) are about as close as you can measure (I can get to 1/4%), but when you go up or down 1/3 speed step and the errors are +3% and -3% !
09-05-2019, 09:41 AM   #7
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FYI:

1) The Topcon SLR came with a negative test strip allegedly taken with that particular body along with a list of actual shutter speeds for each nominal speed on the shutter speed dial.
2) The vast majority of us can just barely distinguish a difference of 1/4 EV exposure in a pair of images.
3) How an image is rendered, how bright the highlights, how dark the shadows, how much in shadow, how much contrast, how much saturation (generally less with overexposure, more with slight underexposure), is very subjective and among any ten Pentaxians looking at an image, there will almost always be some who will want it a shade brighter, a shade darker, with highlights pulled down a bit, with more detail in the shadows, with deeper blacks, with brighter whites. That being the case, there cannot be one single correct right-for-all shutter speed (time value) within plus or minus one half or even three-quarters of an EV step.
4) Post processing can change the recorded exposure by multiple EV steps up or down, washing out everything or turning everything almost black, plus every minute step between. PP can darken highlights, pull detail out of shadows and otherwise modify exposures over a range that makes mockery of concern over 1/3 an EV step of time value when the shutter was tripped.

Back in the film era a piece of advice constantly given: record your exposures so you can get perfect exposures next time. Aside from the huge waste of time of carrying notebooks and jotting down AV, TV and subject every time the shutter release is pressed, which subject and which exposure used six months earlier, or six years earlier is a match for what you are photographing today? Is the tonal range the same, the sun in the same position, the same angle, the same amount of cloud cover or atmospheric haze, is there the same amount of shadow, the same amount of highlight? Is the subject and lighting so nearly identical that only the identical exposure used 12 years before is correct? I always thought that advice the height of absurdity - a pointless waste of time better used to take more pictures, or just to enjoy the place and time

Our digital cameras instantly and faithfully record AV and TV. How many Pentaxians have gone into the EXIF of their own image files to determine an exposure for a picture they are about to take? I think I know how many.

Worried about the accuracy of your shutter lest it give an incorrect exposure? Then turn on auto-bracketing!
09-05-2019, 10:30 AM   #8
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QuoteOriginally posted by WPRESTO Quote
Back in the film era a piece of advice constantly given: record your exposures so you can get perfect exposures next time. Aside from the huge waste of time of carrying notebooks and jotting down AV, TV and subject every time the shutter release is pressed, which subject and which exposure used six months earlier, or six years earlier is a match for what you are photographing today?
For my beginning B&W Film Photography students, I still recommend that they use a photo log but not for the reasons stated. I recommend beginners shooting in manual exposure mode to keep a photo log so that:
a) I can verify that they are shooting the assignment correctly. For example, are they bracketing exposures enough?
b) If something is amiss but they technically used the correct shutter speed and aperture, then this may indicate a problem with the aperture or the shutter.
c) It reinforces the beginning photographer's awareness of their shutter, aperture, and ISO settings and discourages a snapshot approach.

I do agree it is a drudgery to record exposure data and I wish all film cameras were like the Nikon F6 and Pentax 645N that record exposure data on the film edge.
EXIF files are a blessing on digital files; they are invisible but if you need the info, it's there.

09-05-2019, 12:47 PM   #9
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QuoteOriginally posted by Alex645 Quote
For my beginning B&W Film Photography students, I still recommend that they use a photo log but not for the reasons stated. I recommend beginners shooting in manual exposure mode to keep a photo log so that:
a) I can verify that they are shooting the assignment correctly. For example, are they bracketing exposures enough?
b) If something is amiss but they technically used the correct shutter speed and aperture, then this may indicate a problem with the aperture or the shutter.
c) It reinforces the beginning photographer's awareness of their shutter, aperture, and ISO settings and discourages a snapshot approach.

I do agree it is a drudgery to record exposure data and I wish all film cameras were like the Nikon F6 and Pentax 645N that record exposure data on the film edge.
EXIF files are a blessing on digital files; they are invisible but if you need the info, it's there.

For teaching purposes, I can understand, but another point to the pointlessness of recording exposures for the sake of getting it correct later, if you cannot remember the exposure, can you remember which image it was, where and when you took the picture, and then, do you have the log book with you? How many old log books would you need to carry along in the field? It's really a methodology best suited to meticulous work, such as doing scenics or architecture or interiors or studio portraits with a view camera. In the film era, going on vacation I'd take along 30~40 rolls of film, 36 exposures each, roughly 1,000 to 1,400 exposures to record. NO THANK YOU.
09-06-2019, 12:45 AM   #10
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QuoteOriginally posted by WPRESTO Quote
For teaching purposes, I can understand, but another point to the pointlessness of recording exposures for the sake of getting it correct later, if you cannot remember the exposure, can you remember which image it was, where and when you took the picture, and then, do you have the log book with you? How many old log books would you need to carry along in the field? It's really a methodology best suited to meticulous work, such as doing scenics or architecture or interiors or studio portraits with a view camera. In the film era, going on vacation I'd take along 30~40 rolls of film, 36 exposures each, roughly 1,000 to 1,400 exposures to record. NO THANK YOU.
I thought the point of taking notes of the exposure data was to understand how the lens renders at different apertures, what shutter speed is short enough to avoid camera shake with one lens or another, to freeze subjects in motion etc. Not that we should trust notebook(s) rather than the camera for exposure value... But this probably not at all what the OP ("doing an experiment") was asking about.
09-06-2019, 04:57 AM   #11
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QuoteOriginally posted by Subjektiv Quote
I thought the point of taking notes of the exposure data was to understand how the lens renders at different apertures, what shutter speed is short enough to avoid camera shake with one lens or another, to freeze subjects in motion etc. Not that we should trust notebook(s) rather than the camera for exposure value... But this probably not at all what the OP ("doing an experiment") was asking about.
That's an interesting take on it = to "customize" how you use a particular lens based on your experience with it, but that is not what people advocating recording exposure data indicated was the purpose of such discipline back in the film era when I started in photography (late 1950's and especially 1960's onward). As to what shutter speed is suitable to freeze motion of a particular kind, that has surely been tested ad infinitum for many decades and guidelines are only a basic photo book or keyboard click away. My point: recording exposure data in little black books so you can go back and look up a perfect exposure achieved in the past to guide a present exposure for subject & lighting that is "the same" never was even vaguely reasonable. You must have those guidelines from past success in your head. If you don't, you'll never locate them in your stack of little black books.
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