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09-08-2011, 12:29 PM   #1
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SR Question

Ever since Pentax introduced Shake Reduction, and also with the K-5, the user manuals advise us to switch off the SR when the camera is used on a tripod or sometimes when using a flash. I would like to have the reason for this explained. Even on a tripod there might be small vibrations due to mirror action or the wind and the SR should again be helpful in eliminating the effects from the photograph. What goes wrong when a tripod is used with the SR switched on? As I understand the SR has to do two things: 1. Sense the shake, 2. Shake the other way to compensate. So, when nothing shakes the SR should do nothing. Why can the SR not be on permanently? And what is the case when the camera is on a monopod, when only three of the six degrees of freedom are blocked? Shared wisdom will be appreciated.

09-08-2011, 01:04 PM - 1 Like   #2
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Tripod vibration is qualitatively different from hand vibration. It's higher frequency and lower amplitude. The SR system is designed to dampen hand vibration, not tripod vibration.

Why can't SR be on permanently, even when there's no shaking? Because of noise on the SR system. The gyroscopes or accelerometers or whatever they use to sense vibration will emit a bit of noise and that will translate to blur in the image. So SR *can* actually make things worse. I'm not sure about the magnitude of this noise problem, but I think that's the reasoning behind the recommendation to turn off SR on a tripod. The longer the focal length, the bigger the noise problem.

Monopod shake is qualitatively similar to free hand vibration. SR will be a net advantage on a monopod.

Sincerely,
--Anders.
09-08-2011, 01:06 PM   #3
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SR assumes you're handholding the lens and will shake it a little, so it tries to reverse-shake, WHETHER OR NOT you're actually shaking the camera. You can mount a lens on 'pods (tri and mono) and test this: shoot with SR off, then on, and examine the difference.

Or consider: On my K20D, I mounted my big Kenko 180 Fisheye adapter on a A28-80; total weight was >1500g. With SR on, I switched on LiveView and put the camera on a flat tabletop. The SR mechanism caused the camera to shake, and to move around the table.
09-08-2011, 01:12 PM   #4
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I believe it's only a problem if you combine a weak tripod with a large focal length, then the cameras rather powerful SR system might start to shake the entire rig. But with more modest focal lengths and sturdy tripods I doubt you will ever see a problem.

09-09-2011, 01:01 AM   #5
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QuoteOriginally posted by Gimbal Quote
I believe it's only a problem if you combine a weak tripod with a large focal length, then the cameras rather powerful SR system might start to shake the entire rig. But with more modest focal lengths and sturdy tripods I doubt you will ever see a problem.
correct, I ran this test on my tripods and found my small manfroto travel tripod is very shaky especially at full extension and the sr make it worse but on a big Velbon or my beloved Benbo monster it makes no difference
09-09-2011, 07:29 AM   #6
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Camera shake shouldn't be a problem at higher shutter speeds, right? If I'm shooting at 1/250sec then does the SR system do anything - or does it only do negative things at that point? Will I get sharper images without SR and shooting at higher speeds?

I think I should know the answer to this, but somehow keep double-thinking things.
09-09-2011, 07:36 AM   #7
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QuoteOriginally posted by TER-OR Quote
Camera shake shouldn't be a problem at higher shutter speeds, right? If I'm shooting at 1/250sec then does the SR system do anything - or does it only do negative things at that point? Will I get sharper images without SR and shooting at higher speeds?
Falk Lumo posted test results, probably over in the NEWS+RUMORS section, that IIRC showed that SR provides definite gains within a range of focal lengths and shutter speeds, and no IQ loss at higher speeds. So, unlike the old Chevy Corvair, Pentax SR is Safe At Any Speed!
09-09-2011, 07:57 AM   #8
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QuoteOriginally posted by TER-OR Quote
Camera shake shouldn't be a problem at higher shutter speeds, right? If I'm shooting at 1/250sec then does the SR system do anything - or does it only do negative things at that point? Will I get sharper images without SR and shooting at higher speeds?

I think I should know the answer to this, but somehow keep double-thinking things.
Probably as long as you keep it above 1/FL or even 1/(4xFL), it shouldn't do anything. However, if you are using a tripod, there's a good chance that it was because you couldn't use high shutter speed to avoid camera shake.

09-09-2011, 12:42 PM   #9
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QuoteOriginally posted by jcvs Quote
Shared wisdom will be appreciated.
Here is my "wisdom".

1. Much false speculation floats around.

2. Leaving SR on never is a problem except for really long exposures. Therefore, leave SR on when using a monopod.

3. For long exposures, leaving SR on introduces a problem known in engineering as underdampened zero-mode. This means that the sensor may slowly "crawl" away from its initial position. You can actually see this when using a long focal length and 10x magnification in LV on a tripod. There is a tiny and slow movement which disappears when switching SR off. However, using the same experiment, you'll see that walking besides the tripod even on concrete ground has a bigger effect. So, forgetting to switch off SR has no big negative impact. It probably is less than forgetting to use mirror lock up which actually turns off SR anyway. But with exposure times approaching a minute you better follow the user guide's hint.
09-09-2011, 12:55 PM   #10
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Apparently if you use the timer delay release the camera automatically turns off SR for that shot. Assuming you are using that shutter release for the tripod (which you would, unless you were using a remote, and apparently it shuts off SR for that also) then you don't really have to think about it.
09-09-2011, 01:07 PM   #11
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QuoteOriginally posted by GrantMeThePower Quote
you don't really have to think about it.
For really long exposures you have. Because initial trigger vibration damps off enough you don't need a remote, self timer or MLU. But you still would care about SR crawl.

Or with a wired remote. Or a wireless remote connected to the wired plug (these exist and some transmit the LV feed wirelessly which is kind of cool ...).
09-09-2011, 08:53 PM   #12
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SR takes a while to kick in. Even at high shutter speeds if you quickly pan the cam and take a shuit you can get blurred images. I leave it off unless I really need it. Of coure if yuo take soem time to compose your images before shooting then this doesn't' apply. but I'm an impulse shooter of candids
09-12-2011, 01:35 AM   #13
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Don't forget delta fluxus!
09-12-2011, 01:38 AM   #14
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How is it with use on monopod or with shuttertimes like 1/800th ?
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