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Old Feb 1, 2008, 8:17 AM   #1
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Hi all,

Most posts I read concerning using tripods and IS equiped digicams say to turn off IS. Why? I know IS is less important when using a tripod but wouldn't it help none-the-less? Can IS change/degrade a photo where the camera is held absolutely steady?I'm confused, once again.

Dennis
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Old Feb 1, 2008, 9:06 AM   #2
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I have taken photos where the camera is mounted on a tripod, and I forgot to turn off the IS. Most come out fine, but occasionally I've gotten one that contained motion blur due to camera shake, despite the best efforts of the IS system. I was puzzled by this, and suspect that the explanation is this:

The human body will absorb most shake frequencies, and will only transmit, or induce,certain shake frequencies to the camera. My guess is that IS systems are tuned for camera shake when handheld, but other shake frequencies may be outside their range. When a camera is mounted on a tripod, and the tripod receives a sharp blow, it will vibrate at a frequency that may be outside the range that the IS system is capable of dealing with.

I would, of course, be pleased to read what others might think.
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Old Feb 1, 2008, 11:08 AM   #3
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While I in no way disagree with TCav the explanation I have read is that the IS system itself introduces vibrations. It seems conceivable that hands normally absorb these vibrations whereas tripods do not.

Unfortunately I see no way to get any closer to reality without a vibration analysis lab.

This is also an area that I haven't explored having never switched off IS nor usedmy cameraon a tripod. I have used it handheld+monopod but there was enough opportunity for subject motion blur that one couldn't have made any IS judgements anyway.
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Old Feb 1, 2008, 12:29 PM   #4
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Google can be your friend - and something I should have done prior to my post. :idea:

This article refers to in-lens IS and self-induced image blur when the camera is stabilized and IS is on:

http://digital-photography-school.com/blog/image-stabilization-on-tripods/

I now wonder if it's the same for in-body IS? I'll call Olympusand post again.

Thanks for your help TCav and ac.smith.

Dennis

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Old Feb 1, 2008, 1:27 PM   #5
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The link you provided contains the following quote:

"The IS mechanism operates by correcting shake. When there is no shake, or when the level of shake is below the threshold of the system's detection capability, use of the IS feature may actually *add* unwanted blur to the photograph, therefore you should shut it off in this situation. Remember that the IS lens group is normally locked into place. When the IS function is active, the IS lens group is unlocked so it can be moved by the electromagnetic coil surrounding the elements. When there's not enough motion for the IS system to detect, the result can sometimes be a sort of electronic ‘feedback loop,' somewhat analogous to the ringing noise of an audio feedback loop we're all familiar with. As a result, the IS lens group might move while the lens is on a tripod, unless the IS function is switched off and the IS lens group is locked into place."

That quote is attributed to Chuck Westfall of Canon.

It would seem to me that, if Canon knew about it, Canon would have done something about it, which makes me doubt this explanation.

Another explanation I've read is that the gyroscopes that measure camera shake will induce the camera shake. This explanation is absurd because there are no gyroscopes in IS systems. They use strain gauge accelerometers to measure camera shake, and strain gauge accelerometers don't have any moving parts (or, more precisely, the parts that move are microscopic, and the movement is so small an opticalmicroscope wouldn't detect it.)

And wheneverI read either of those explanations, the question that immediately pops into my head is this: Once the camera is shaking, whether the shake originated from the camera itself or not, why wouldn't the IS system compensate for it?
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Old Feb 1, 2008, 2:31 PM   #6
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TCav wrote:
Quote:
The link you provided contains the following quote:

"...When there is no shake, or when the level of shake is below the threshold of the system's detection capability, use of the IS feature may actually *add* unwanted blur to the photograph, ...


It would seem to me that, if Canon knew about it, Canon would have done something about it, which makes me doubt this explanation.


And wheneverI read either of those explanations, the question that immediately pops into my head is this: Once the camera is shaking, whether the shake originated from the camera itself or not, why wouldn't the IS system compensate for it?
The quote from Canon suggests to me that they've designed an unstable or marginally stable circuit (using positive feedback rather negative feedback) to speed circuit response time. In the absence of signal the circuit drops into oscillation and the blur is caused, notby inducing vibration of the camera but rather uncommanded movement of the correcting lenses.

Canon has recognized their problem "Yes, there is always an exception to any rule and in the case of IS it is important to know that there are some DSLR lenses that can actually sense and account for when you're using a tripod (Canon calls it tripod detection - a feature that was added in 2000)"

This points to another factor that may make for variability observed between different systems. Themass of the moving elements in P&S lenses will be less than those in DSLRs so it should be simpler to design a fast, stable OIS circuit in a P&S. Likewise I suspect the sensor in a DSLR could be lighter than the correcting lens elements yielding apractical advantage to the sensor movement systems.

Again I'm speculating without access to the engineering white papers.

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Old Feb 2, 2008, 12:19 AM   #7
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TCav wrote:
Quote:
And wheneverI read either of those explanations, the question that immediately pops into my head is this: Once the camera is shaking, whether the shake originated from the camera itself or not, why wouldn't the IS system compensate for it?
The answer is in something called 'dither'. In either system, there has to be mechanical movement to compensate for the camera shake. Any mechanical system has friction. The two basic types of friction are static and dynamic. The force required to overcome static friction is considerably greater than that required for dynamic, therefore the motion control systems are designed with a small, high frequency motion built in, so the compensating movements have only to overcome the dynamic friction, requiring a simpler control algorithm. Many people notice a slight 'buzz' when the IS system is operating.

Designing a system to exactly counter external movement is quite a difficult task, and when you add in the requirement of minimal power use for hand held cameras it could be quite frustrating. In any case, turning off the IS when you don't need it will prolong your battery life.

brian


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Old Feb 2, 2008, 1:35 AM   #8
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i use a tripod with my canon S3. and never had the IS turned off. and i love using the zoom. to take pictures of birds. and i haven't notice any blurring. i will have to take picture with it on and off. to see if i can see a difference.
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Old Feb 2, 2008, 11:28 PM   #9
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I have just completed a series of tests with my Kodak Z612. I mounted the camera on my lightest weight tripod, a35 yr old Sunset GD-3000 and took pictures with the IS set to continuous, single-shot and off. Each series consisted of two shots fired by the self-timer and an 8 shot burst which required me to keep my hands on the camera. The test was then repeated with my heaviest tripod, a 30+ year old Quick-Set Highboy IV. Both tripod were extended to put the center of the lens at 5'1" from the floor (my eye level).

I examined all photos and could find no discernible difference whether IS was on continuously, single-shot or off. The exposure time was on the order of 1/10 sec. and the lens was zoomed to about 155mm equiv. These results can't be extrapolated to any other system and may not even be extrapolatable to slower shutter speeds on the z612 however I doubt I'll be concerned about turning IS off when using a tripod.

I won't load all the photos but I will load a 100% crop of one in each state of the IS.

The first photo is the overall scene. EXIF available on all photos.
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Old Feb 2, 2008, 11:32 PM   #10
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100% crop, IS - continuous, self-timer triggered, Quick-Set tripod.
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