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03-22-2012, 10:47 AM   #1
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Fast shutter speed accuracy problems

I'm experiencing shutter accuracy problems at fast shutter speeds with my K-r. The camera will underexpose at shutter speeds of 1/2000 and faster, progressively worsening as the speed approaches the 1/6000 limit.

The shutter count is 30,746. The images below are shot at 1/1600, 1/3200, and 1/6000, respectively.

Is this the result of shutter wear, and should I be concerned about this condition? Can anyone else reproduce this behavior? If so, note the shutter count of your camera and the shutter speed at which exposure accuracy begins to degrade.

--DragonLord

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03-22-2012, 11:00 AM   #2
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Hmm I had a problem with my K-r where it would randomly underexpose (pretty severely, very dark photos) in bright high shutter speed conditions.

Here is how I described it then:
"When out shooting in the daylight, I would take a photo of a subject (well lit, for example a no parking sign on a brick wall), sometimes the image would show as almost black (very underexposed) on my screen, next shot would show perfect exposure, but the ISO, shutter speed ,f stop, settings, lens and subject were all the same from one shot to another. AF, center point, jpegs. This happened with a couple of lenses (F28 and DA15) many times during a day of shooting, seemingly randomly, I dont think the AF was choosing a dif subject for focus. You could take 5 shots of the same point and maybe 3 would be black and two good, then you could take another 10 and they would be ok, it popped up randomly."

I couldnt find what caused the issue, neither could Pentax, so they just replaced it. I have a K-5 now

Not sure if this is the same issue or not. The thread for my issue is here, not much response to it and sadly I deleted the sample photos. But they were almost black. The camera would take great shots and then randomly produce a dark shot.
https://www.pentaxforums.com/forums/general-technical-troubleshooting/150836-...tos-black.html
03-22-2012, 11:10 AM   #3
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The problem I'm experiencing is not random, but is consistently reproducible and worsens with increasing shutter speed.

--DragonLord
03-22-2012, 11:12 AM   #4
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It also seems to look darker near the top of the images

QuoteOriginally posted by DragonLord Quote
The problem I'm experiencing is not random, but is consistently reproducible and worsens with increasing shutter speed.

--DragonLord
Likely best to just send it in if you have warranty left

03-22-2012, 11:16 AM   #5
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QuoteOriginally posted by Deimos Quote
It also seems to look darker near the top of the images



Likely best to just send it in if you have warranty left
The warranty expired 4 1/2 months ago.

As I stated before, the shutter is probably starting to wear out. In any case, I am upgrading to the K-5; I'm trying to see whether this camera can still be used as a backup.

--DragonLord

Last edited by bwDraco; 03-22-2012 at 11:24 AM.
03-22-2012, 11:21 AM   #6
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QuoteOriginally posted by DragonLord Quote
The problem I'm experiencing is not random, but is consistently reproducible and worsens with increasing shutter speed.

--DragonLord
Then the reasonable conclusion is that the shutter is not actually reaching those speeds. Reading your exifs, it looks like the aperture and ISO settings are correct for each stop of shutter speed on the same subject.

If you take teh 1/3000s picture and the 1/6000s picture and redo them to see what ISO settings are required to get the same shot as the 1/1500s picture (or even try pulling exposure up in Lightroom), you may be able to determine what the actual shutter speed is.
03-22-2012, 11:34 AM   #7
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QuoteOriginally posted by JinDesu Quote
Then the reasonable conclusion is that the shutter is not actually reaching those speeds. Reading your exifs, it looks like the aperture and ISO settings are correct for each stop of shutter speed on the same subject.

If you take teh 1/3000s picture and the 1/6000s picture and redo them to see what ISO settings are required to get the same shot as the 1/1500s picture (or even try pulling exposure up in Lightroom), you may be able to determine what the actual shutter speed is.
Using RawTherapee, exposure adjustment is +1 EV for the 1/3200s image (actual shutter speed 1/6400) and +1.5 EV for the 1/6000s image (actual shutter speed 1/16000). In addition, for the 1/6000 and 1/3200 images, the top is darker than the rest of the image after adjustment; the effect is more pronounced with the 1/6000 image. This is a clear sign the shutter is wearing out. As stated before, I am upgrading to the K-5.

--DragonLord

Last edited by bwDraco; 03-22-2012 at 11:44 AM.
03-22-2012, 11:39 AM   #8
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Actually, in thinking about it again - a shutter that is running slower than it should will expose an image brighter. You double the shutter speed, and the aperture halved in response (to get the same exposure). Therefore, if the picture is darker, the shutter speed must be even faster. And if you say it took +1EV to adjust it properly, that means your 1/3000s is actually shooting at 1/6000s, and the 1/6000s is shooting at 1/15000s. Which seems odd to me.

It's an interesting situation - I'm stumped.

03-22-2012, 11:47 AM   #9
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It seems the first curtain of the shutter is opening later than it should be.

Is anyone else able to reproduce this problem?

--DragonLord

Last edited by bwDraco; 03-22-2012 at 11:54 AM.
03-22-2012, 12:16 PM   #10
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QuoteOriginally posted by DragonLord Quote
The warranty expired 4 1/2 months ago.

As I stated before, the shutter is probably starting to wear out. In any case, I am upgrading to the K-5; I'm trying to see whether this camera can still be used as a backup.

--DragonLord
They say its good for 100k so perhaps it will be covered even if the 1 year is up?
03-22-2012, 12:43 PM   #11
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before you go running off to get a new shutter answer a few questions.

first of all, it looks like you used a tripod, did you cover the eye peice? that could really screw up anything you are doing.

next, turn off pattern metering and put spot metering on, this will avoiid any inconsistencies due to vignetting, which is clear in the lens.
It also might be more realistic to work between F4 and F5.6 because at F2.8 and below vignetting and other issues are worse, and the middle apertures are likely much more accurate. this is especially true since F2.8 is the maximum aperture, maximum and minimum aperture are the most likely to be slightly off on any lens,

use aperture only to offset shutter speed, not ISO, you are changing too many variables at once.

Having said all that, one thing I really miss in camera reports these days is the tests done on shutter accuracy. Popular Photography ( i think, or maybe Modern Photography) used to publish exposure accuracy curves, the top end of many cameras could easily be shown to be out by 1/3 or 1/2 stop in those tests.your drift from 1/6000 to 1/3200 ( which is not a full stop to begin with) is 25 greyscale, and that is about 1/2 stop) what is more of a concern is the over exposure at F4 and 1/600, shich is about 1.5 stops above where t should be.

did you shoot these in RAW or JPEG? they should be JPEG neutral, with no shadow or highlitght protection and no contrast adjustment

Last edited by Lowell Goudge; 03-22-2012 at 12:49 PM.
03-22-2012, 12:58 PM   #12
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QuoteOriginally posted by Lowell Goudge Quote
before you go running off to get a new shutter answer a few questions.

first of all, it looks like you used a tripod, did you cover the eye peice? that could really screw up anything you are doing.

next, turn off pattern metering and put spot metering on, this will avoiid any inconsistencies due to vignetting, which is clear in the lens.
It also might be more realistic to work between F4 and F5.6 because at F2.8 and below vignetting and other issues are worse, and the middle apertures are likely much more accurate. this is especially true since F2.8 is the maximum aperture, maximum and minimum aperture are the most likely to be slightly off on any lens,

use aperture only to offset shutter speed, not ISO, you are changing too many variables at once.

Having said all that, one thing I really miss in camera reports these days is the tests done on shutter accuracy. Popular Photography ( i think, or maybe Modern Photography) used to publish exposure accuracy curves, the top end of many cameras could easily be shown to be out by 1/3 or 1/2 stop in those tests.your drift from 1/6000 to 1/3200 ( which is not a full stop to begin with) is 25 greyscale, and that is about 1/2 stop) what is more of a concern is the over exposure at F4 and 1/600, shich is about 1.5 stops above where t should be.

did you shoot these in RAW or JPEG? they should be JPEG neutral, with no shadow or highlitght protection and no contrast adjustment
The camera was not on a tripod, but was simply supported on a railing. I was looking through the finder when I shot these images. The images were shot in JPEG, without any dynamic range adjustment.

--DragonLord
03-22-2012, 01:30 PM   #13
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OK that simplifies things, next is to do this in spot metering.
03-22-2012, 02:06 PM   #14
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If you purchased the camera new with a credit card it may have card insurance that extends or doubles the warranty period of anything bought with it. My visa is like this
03-22-2012, 03:03 PM   #15
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I'll use the procedure outlined at You already own a shutter tester to determine whether the shutter is indeed faulty. I have access to a functioning CRT TV at home, but I'm away at this time and won't be able to do this until later tonight.

--DragonLord
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