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07-22-2010, 03:29 PM   #46
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QuoteOriginally posted by nanok Quote
could this have something to do with the stopping action of the first curtain
We quote the first curtain stop event as one possible cause. Note however that you need an additional non-linear effect to cause a difference between a smooth and a hard stop. Both stops have the same "Kraftstoß" Ft (no direct English translation?).

It came as a surprise to us when the measurements revealed that the curtains are actively decelerated and that the "slit" doesn't have a constant width. The curtain stop events are loud but most of the energy was destroyed before.

QuoteOriginally posted by dlacouture Quote
Furthermore, from memory, the SR sensors can truly compensate for "rotational" shake only, not translations (I don't even know if gyros are capable of accurately detecting a translation!)...
Translations cannot be measured but could be compensated from a precomputed table. However, the SR control loop is designed with about 50 Hz bandwidth in mind while the sensor position control loop probably is hardwired in the KHz bandwidth range (guessing from our simulation). It would have to be made to respond faster.

QuoteOriginally posted by nanok Quote
i think they are using accelerometres to be precise
They don't. It's three semiconductor angular velocity sensors (gyros) measuring the Coriolis force. It's even depicted in the study where we cite the SR patent. The exact make and perfomance of these sensors have been discussed elsewhere already.

07-22-2010, 04:12 PM   #47
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QuoteOriginally posted by falconeye Quote
Blur at 300mm and 1/100s is not dominated by shutter blur.
I meant ineffective above 1/100s, not at 1/100s, like focal lengths of 300mm. I'm assuming shutter speeds of around 1/300.
QuoteQuote:


Look, to see this in detail: shutter blur depends on the exposure time and maxes at about 1/100s. But it is almost independent of focal length and of shake reduction in operation or not. Call this blur B(t).
Side question: why is it independent of focal length? If the magnitude of the shake of the camera (say, distance where the sensor is) is fixed above 1/100s, a larger focal length will still magnify the image (and thus the shake) linearly, as with your later a*f*t term. If it is because you say it decreases proportionally with the exposure time due to it not capturing all of the shutter-induced-shake, it is misleading to say it is independent of focal length: when you increase focal length, you do not necessarily decrease exposure time.
QuoteQuote:

Free hand shake is mostly from camera rotation. Mostly proportional to both, focal length f and exposure time t. It is reduced by shake reduction where SR may reduce this to say 1/3. Call this blur A. With A = a f t. And shake reduction may reduce a to a' = a/3 or so.

Together, you have B(t) + a f t or B(t) + a' f t.

So, if you measure the sum, it may be that B(t) is too large to see the difference between a and a'. And because you cannot increase t (B(t) becomes 0 for large t) you have to increase f to see it. This is what you do when using a 300mm lens.
This is what I was getting at, unless I am still missing something. I stated that if it is shutter blur dominated (B(t) is too large to see the difference between a and a'), how can you say
QuoteQuote:
Early efficiency tests of the K-7 shake reduction suggested that it may be ineffective at fast shutter speeds as required for long focal lengths. This was a preliminary conclusion we proved to be wrong. The Pentax shake reduction is effective even at 1/500s!
?

Yes, the conclusion is wrong, I would agree with that. But my understanding is that due to ambiguities, the test is inconclusive. But you state the reverse of the original conclusion: it is effective even at 1/500s. So there's my original question: what lets you assert that SR is effective at 1/500s?

Last edited by Eruditass; 07-22-2010 at 04:35 PM.
07-22-2010, 04:19 PM   #48
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Just a bit of stuff

Interesting patent

Focal Plane Shutter Device For A Camera - Patent 5489960
07-22-2010, 04:30 PM   #49
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QuoteOriginally posted by dlacouture Quote
I'd say that shake blur is slow and of great amplitude, whereas this shutter blur is ultra fast and small, so they are pretty different.
I said empirically impossible, as in you can measure them separately. I believe my statement is true (you can't measure them separately, both are functions of t and f)

I agree that they are quite different other than that.
QuoteQuote:

Another thing to take into account is that this effect will be smaller for every addition of weight, and long lenses often are heavier than wide angles.
I've seen this blur from time to time with my 18-55 (especially in the portrait orientation), but never with the hefty 70-200/2.8...
Makes sense, there is probably a fixed amount of force induced by the shutter. Newton's Second Law.
QuoteQuote:

Furthermore, from memory, the SR sensors can truly compensate for "rotational" shake only, not translations (I don't even know if gyros are capable of accurately detecting a translation!)...
This was a misprint from a K10D document, only(?) the K-7 has rotational compensation, the rest are translational.


Last edited by Eruditass; 07-22-2010 at 04:37 PM.
07-22-2010, 04:31 PM   #50
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QuoteOriginally posted by jeffkrol Quote
We came across this stuff in our research as well. Counterbalanced shutters are heavier overall though and haven't been a large success it seems.
07-22-2010, 04:31 PM   #51
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I will wait for the next rainy day to read all the posts. Just curious, what temperature and humidity did you conduct this "simulation". Did you have a chance to try this with the grip attached and maybe loaded with heavy Eneloops. I wonder if this might change the window of unwanted oscillations.

Cheers, Mike.
Just read the part about 6 eneloops. Never-mind.

Last edited by Ex Finn.; 07-22-2010 at 04:51 PM.
07-22-2010, 04:39 PM   #52
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QuoteOriginally posted by Eruditass Quote
So there's my original question: what lets you assert that SR is effective at 1/500s?
If you look at cluttered Fig.3 ( http://www.falklumo.com/lumolabs/articles/k7shutter/images/extrablur.png )

and try to single out the four 300mm curves, you see that it works pretty well at 2ms. This is possible because shutter blur (the B(t) term) is almost zero for small t<1/200s too. At the time the earlier and wrong conclusion was drawn, we did not have this data.
07-22-2010, 05:14 PM   #53
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Just glanced at your test report, well done.
I was wanting a second K-7 body for cheap, cant wait for the price drop.

Cheers, Mike.
p.s. thank god for focus-magic.


Last edited by Ex Finn.; 07-22-2010 at 05:26 PM.
07-22-2010, 05:32 PM   #54
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QuoteOriginally posted by Eruditass Quote
Side question: why is it independent of focal length?
Thinking outloud: This suggests that the perturbation is not of rotational nature. Otherwise, focal length should have a significant impact.

The blur caused by a translational displacement (camera move as a re-actio to the shutter move) depends on the magnification. The latter not only depends on the focal length but also on the distance. From the top of my head I'm not sure to what extent the study went into this issue.

It probably is the case that the blur is created through a combination of effects and that it might not be entirely independent from focal length (just not dominated by it).

QuoteOriginally posted by Eruditass Quote
...the K-7 has rotational compensation, the rest are translational.
Just to clarify this: To the best of my knowledge Pentax SR detects yaw and pitch rotation and compensates it with a 2D displacement of the sensor. The K-7 is the first to also compensate roll rotation (which is obviously compensated by sensor rotation, not displacement).
07-22-2010, 05:33 PM   #55
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QuoteOriginally posted by Ex Finn. Quote
p.s. thank god for focus-magic.
Good advice. Don't forget to use the motion blur module...

Attached: the study's opening image. Then treated with Focus Magic. This will blur the text of course as it wasn't blurred before. So, look at the image, not the text.
Attached Images
View Picture EXIF
PENTAX K-7  Photo 
View Picture EXIF
PENTAX K-7  Photo 
07-22-2010, 05:45 PM   #56
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QuoteOriginally posted by Class A Quote
It probably is the case that the blur is created through a combination of effects and that it might not be entirely independent from focal length (just not dominated by it).
Yes. I wrote about it a bit here (in German language): DigitalFotoNetz.de :: Thema anzeigen - LumoLabs: Verschluss-induzierte Unschärfen bei der K-7

The exact treatment requires a classical mechanics calculation I was too lazy to do. I think the ratio of distances from the focal plane to 1. center of gravity and to 2. nodal point comes into play here. This ratio should change more slowly than the focal length itself.

Also, as we define shutter blur for zero magnification (infinite distance), a pure displacement of the body does not create blur, but a soft-coupled sensor does.
07-22-2010, 05:46 PM   #57
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QuoteOriginally posted by falconeye Quote
Good advice. Don't forget to use the motion blur module...

Attached: the study's opening image. Then treated with Focus Magic. This will blur the text of course as it wasn't blurred before. So, look at the image, not the text.
That is a good demonstration. I personally use out of focus correction 98% of the time, 1 or 2 pixels usually. Hardly ever need the motion blur correction, effective as it is.

Cheers, Mike.
07-22-2010, 06:18 PM   #58
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falk: thank you for setting me straight. my appologies, i did mention i haven't had the chance to read the full article yet (i was at work, crazy day too). very interesting what you found out about the deceleration and the slit size (i expect it becomes smaller with the deceleration, to keep the exposure even across the frame?). i wonder if this wouldn't affect the shape of fast moving objects near the edge of the frame, at fast shutter speeds (the deformation happens anyway, with focal plane shutter, in theory). anyway, that's a different story.

i am wondering, is it possible that the added complexity of this active deceleration mechanism induced this "bug"? is there an easy way to determine if a k20d shutter behaves the same way, or is an "honest" vertical travel shutter instead?

coriolis sensors: hmmm, nifty, i didn't know that's what they used. a whole different discussion on it's own though. sorry for spreading wrong info.

i'll stop asking questions, and go read your full article first, before i become trully annoying. thanks for being so patient.

ps: kraftstoss: i would call it kinetic energy here, though i don't think it's anywhere near a direct translation. german is such a wonderfully precise language . if i understand correctly, dimesnionally it is impulse (so calling it energy is..ahem.. strictly wrong, but will probably get the point across), i guess it's "stopping impulse" or something like that.
07-23-2010, 06:48 AM   #59
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QuoteOriginally posted by Eruditass Quote
This was a misprint from a K10D document, only(?) the K-7 has rotational compensation, the rest are translational.
Beware! The sensor can indeed translate (and rotate on the K7), but this does not mean it can compensate for translations of the camera!

In fact, only rotations of the camera can be somewhat compensated, translations cannot, as it depends on others parameters (unknown by the camera).

Thinking of it, rotations can only be partially compensated, as you then fall into the optical problem met in panoramic shoots where you have to rotate your whole system around the lens' nodal point, else you'll have parallax problems...

Thankfully, we're talking about really small angular displacements here, so they can be handled by a mere translation of the sensor, but this is an approximation.

In fact, the sensor-based SR implementation would have been better suited for compensating translations of the camera, but those don't have any real impact on the pic except for macro work (and you would have to somehow input the focus distance and magnification anyway!).

Now, regarding the possible firmware fix (one can always dream) :
as they cannot possibly do a full study of all lens/grip/flash combinations out there, could it be possible to derive the needed SR countermove from the gyros readings?
Not for the actual shutter shake (as it seems impossible), but rather to have a pretty rough idea of how the camera is handled, and then adjust the shutter-shake pre-recorded removal pattern accordingly and send it to the SR module...

If the gyros are extra-still, then you can conclude we are on a super-strong tripod: Shutter-shake removal pattern for this shutter speed should be disabled.

If they are all over the place, then you have a light lens and/or a bad holding hand: Shutter-shake removal pattern for this shutter speed should be at full power...

If they are moderate, then you either have a bad tripod, or an heavy lens/flash/grip... The removal pattern would still be needed, but not as much...

With accurate mathematical modeling, I'm pretty sure they can pull this off... And the results would certainly be better than nothing.
07-23-2010, 09:42 AM   #60
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Gyros extra Stills?
Mmm my k7 on tripod (manfrotto 190db on very stable flood) with a tamron 500/8 was overcompensating to thé point the SR in LiveView wasoving all the time: inusable.
Deactivating SR cured the thing.

So I'm not sûre thé gyros are *that* reliable.
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