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07-21-2010, 03:54 PM   #16
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QuoteOriginally posted by dlacouture Quote
What could be done by firmware would be to counter this curtain-induced sensor shake (taking into account the actual orientation of the camera), by mapping this shake with accelerometers and overlaying this to the SR loop...
Maybe they already do this and it's just not calibrated enough.

The do need to fix this as the K-7 has just become a no-buy for many people. It's definitely not a "pro" camera.

07-21-2010, 04:12 PM   #17
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Wow! Great job!

These results match my own observations quite well. I sometimes run into that kind of dreaded blur when using my K-7 with the 16-45mm, especially from wide angle to standard (16 to 35mm).

Since then, I've learned that I could work around that issue by cranking up the ISO to achieve higher shutter speeds when possible, (say from ISO 100 to ISO 200, to go from 1/100th to 1/200th of a second, for example), or by going for slower shutter speeds when boosting the ISO is not possible. I also noticed that this blur is more present on photos taken with the drive mode set to burst-Hi (5.2 fps)...

I must admit it took me quite a while to figure out that the blur was mostly present at these shutter speeds (1/90th, 1/125th, etc).

But most important, I did not understand the reasons why shutter speeds around 1/100th of a second were resulting in more blur than slower shutter speeds.

I thought my hand shake was most problematic around these shutter speeds, so I just tried to avoid these when I could — not much of an issue, since I often shoot in very low light (with shutter speeds around 1/50th or less) or in bright daylight (with shutter speeds in excess of 1/250th of a second).

This in-depth analysis of the issue sheds new light on the issue. Now I'll know exactly what to do when I run into these problems.

Thank you very much, Falk! Much appreciated!

Last edited by tigrebleu; 07-21-2010 at 04:17 PM.
07-21-2010, 04:15 PM   #18
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QuoteOriginally posted by Aristophanes Quote
Maybe they already do this and it's just not calibrated enough.

The do need to fix this as the K-7 has just become a no-buy for many people. It's definitely not a "pro" camera.
Oh yeah you're certainly right
07-21-2010, 04:26 PM   #19
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QuoteOriginally posted by Aristophanes Quote
Maybe they already do this and it's just not calibrated enough.

The do need to fix this as the K-7 has just become a no-buy for many people. It's definitely not a "pro" camera.
Well, they've made changes to SR firmware in the past, at least from their descriptions, so they apparently have the capability.

07-21-2010, 04:44 PM   #20
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Thanks for all your encouragement.

I'll go thru some of the questions now, trying to help out where I can.

QuoteOriginally posted by opiedog Quote
seems like this is a function of the higher FPS of both cameras. k20's much less affected and i haven't notice that on my k200.
I'm not sure why this is. The faster shutter by itself shouldn't cause more blur than a slower one. But a heavier one should (effective weight of moving parts). We don't believe that the shutter is this much heavier. Something else is involved. So, it isn't the faster FPS. Just bad luck.

QuoteOriginally posted by RonHendriks1966 Quote
Would putting the SR to off have any influence or is that not blocking the sensor at his place?

By the way do you have the report also as a pdf-download in Deutsche Sprache?
Switching SR on or off has no impact on the effect itself. We don't recommend to switch off SR as it does still reduce blur due to free hand shake.

To help understand: the movements due to SR are slow and large compared to the movements of the camera body during the time the shutter moves (fast and small).

Sorry, report's original is English language. Would be German if Leica had the problem though

QuoteOriginally posted by philbaum Quote
Of course, what Wikipedia doesn't address is the impact of the shutter motion on the SR behavior of Pentax like cameras. But it certainly supports Falks report conclusion that shutter motion is involved in the problem.

Questions:
1. It seems to me that Pentax's decision to go to higher shutter speeds (which of necessity would speed up the first and second curtains as a constant, i think) contributed to this problem - am i right on that?
K20D: max shutter speeed 1/4000
Kx: max shutter speed 1/6000
K7: max shutter speed 1/8000

2. If Pentax wanted to eliminate this nick blur problem, could they issue a firmware change that would reduce maximum curtain speed and of course, reduce maximum shutter speeds. (On the Kx, this would also have the likely side effect of reducing curtain noise as mentioned by Wikipedia)

3. Is it practical to use Live View as a way of eliminating first curtain vibration and mitigating this problem as suggested by the Wikipedia article. The K20 doesn't have good Live View implementation so i can't address this. I'm so used to a good optical viewfinder, not sure i would want to use Live View for framing.

Thanks again, real progress of course in understanding the problem.
Ad Wikipedia: The K-7 and K-x don't use an electronic first curtain in Live view (LV) or mirror lockup (MLU). In LV, the shutter is closed first before the actual exposure starts with opening the first curtain again. So, the Wikipedia article does not apply.

Ad 1. Maxiumim shutter speed is controlled by the accuracy of the slit size, not the travelling speed. A higher speed shutter simply is more high quality precision engineering.

What requires a higher travelling speeds is a faster flash sync time (1/180s in all three cases). And possibly a very high FPS rate.

However, as said above, the travelling speed cancels out of equations. Mass and distance are the only parameters which matter. At least as fas as the effect of body movement is concerned. The non-linear effect is ... non linear. So here, speed and accelarations may indeed play a role.

Ad 2. In any case, we don't advise to change shutter curtain speed and BTW, it wouldn't be feasible anyway.

Ad 3. Like SR, LV and MLU have no impact on the effect.

QuoteOriginally posted by Gimbal Quote
One "non-linear term" that might cause problem for the SR is mechanical friction in the suspension of the image sensor plate. It can very well lead to small "jumps" when the SR system wants to move the plate a very small distance.

And there are friction as we can easily test by tilting the cameras and listen to the sensor sliding around, some cameras even needs to be knocked a little before the sensor starts sliding, "Starting friction" in action.
Unlikely but not impossible.

QuoteOriginally posted by dlacouture Quote
What could be done by firmware would be to counter this curtain-induced sensor shake (taking into account the actual orientation of the camera), by mapping this shake with accelerometers and overlaying this to the SR loop...

As it seems to be quite repeatable and constant from one camera to the next, it could work (if the SR loop is not hardwired!), but at the expense of a huge work by Pentax...

And even then, it will greatly depend on what you have on the camera at the time, I think : additional weight (think Grip, Flash and Lens here) will surely lessen the curtain effect by decreasing the curtain/camera weight ratio...

So, as much as I'd like to see this solved on both models, I don't have much hope...
I wrote something similiar elsewhere.

This is actually a nice aspect about SR: it could be programmed to counteract the shutter effect (cancellation approach). As you write, only perfect for a single body weight/lens combination. But should still help in general.


Let me complement with this thought:

If the body moves in counter reaction to the travelling masses of the shutter, then the magnetically floating sensor could just "slide" to not participate in body movement. The magnetic forces could be changed to just G-force with the feedback loop switched off (during the time a curtain travels). This should still be better than to try to follow the kick-n-stop body movement and to possibly overshoot afterwards (if this is what is happening).


So, a camera with a mechanical focal plane shutter and a floating sensor could be the perfect camera free of any shutter-induced perturbation.

Last edited by falconeye; 07-21-2010 at 04:49 PM.
07-21-2010, 06:14 PM   #21
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Your article is everywhere now. Any new models at Photokina will be scrutinized immediately for this effect. And Pentax has an issue that may cost $$$$$$$ to fix.

Oh, yes. And you just driven a dagger through current sales. Happy? :-)
07-21-2010, 06:25 PM   #22
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well, not all K7's nor all Kx's have the issue.

does the majority have it? maybe, maybe not. so there's yet another "unknown" factor.

i definitely would like the issue fixed.

will it affect sales, probably, but there's no need to be harsh

falk,
you mentioned that you gave a copy to pentax (germany, japan, france, us?). was it to a manager, tech, or engineer?
hopefully, someone high-enough in the chain to understand and make a difference.
07-21-2010, 06:31 PM   #23
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QuoteOriginally posted by Aristophanes Quote
Oh, yes. And you just driven a dagger through current sales. Happy?
We discussed the issue with Pentax first. It helps everybody.
QuoteOriginally posted by opiedog Quote
you mentioned that you gave a copy to pentax (germany, japan, france, us?). was it to a manager, tech, or engineer?
hopefully, someone high-enough in the chain to understand and make a difference.
Executive level manager, both acknowledging the problem and appreciating our work. One of the problems is that it may be a rare case where technical information flows in the "wrong" direction. They are working at that


Last edited by falconeye; 07-21-2010 at 06:36 PM.
07-21-2010, 06:52 PM   #24
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Phenomenal work. I know the K20 did not exhibit the problem, but out of curiosity, did you mount up any other camera brands?
07-21-2010, 07:31 PM   #25
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Falk, as always I admire your scientific spirit. Your stellar work sounds like an elaborate proof of a good reason (among others) not to always prefer a smaller/lighter camera body - less mass to dampen vibration!
07-21-2010, 08:04 PM   #26
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QuoteOriginally posted by opiedog Quote
well, not all K7's nor all Kx's have the issue.

does the majority have it? maybe, maybe not. so there's yet another "unknown" factor.
I wonder if there's a human factor involved too, not just the camera? The blur seems to me to be a harmonic disturbance. Harmonics are generated under certain conditions. Change the conditions and the results change. The fact that a good tripod eliminates the problem points to the fact that grip is significant, and so is the 50% margin measured in the test.

I am an excellent shot with a rifle. I believe some of that technique also relates to photography. I tested my K-x at 1/60, 1/125 and 1/250s and none exhibited blur. That may be because my camera is different somehow, or maybe I hold the camera differently (softer, harder, looser, steadier?). Or maybe my testing wasn't thorough enough.


I suspect someone will use this work to criticize in-body shake reduction.... Fast shutter speed generates oscillation in the sensor, causing blur in the image.
07-21-2010, 08:08 PM   #27
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QuoteOriginally posted by KjetilH Quote
Use CTRL+F and type "rotat", at least there is claims from Pentax about 'rotational SR'. Seems to have been there from the K100D.
When the K-7 was released Pentax admitted that all models prior to the K-7 had the rotational compensation advertised but not implemented. Allegedly, the feature got into the adverts by a "translation error".

QuoteOriginally posted by Aristophanes Quote
The do need to fix this as the K-7 has just become a no-buy for many people. It's definitely not a "pro" camera.
Maybe Benjikan will switch to a K-7 now. He likes the blurred look he gets by dragging the shutter when using flash.

QuoteOriginally posted by opiedog Quote
well, not all K7's nor all Kx's have the issue.
How do you know?

QuoteOriginally posted by Aristophanes Quote
And you just driven a dagger through current sales. Happy? :-)
I think we all know that Falk only means well for Pentax. I also know that he has given them quite some grace period to react before he went public with the results.

QuoteOriginally posted by falconeye Quote
We discussed the issue with Pentax first.
Are you in a position to tell us what their reaction was? I hope Pentax Japan didn't ignore you.

The source of the problem might lie with Copal (who I understand manufacture the shutters for the K-7) rather than Pentax. Still something Pentax has to sort out. Also, it might be a matter of how the shutter is built into the casing.

EDIT: I just completely read the article (got side-tracked with the Understanding Image Sharpness White Paper) and agree that it is likely that the SR controller has a role to play as well.

P.S.: Amazing work. Chapeaux to all authors and co-authors.
One major result is clear: Real engineers shoot Pentax!

P.P.S.: Pentax needs to start selling "Class A" tripods. Surely people will buy more of these now. Looking at my username, perhaps I should start selling them?

Last edited by Class A; 07-21-2010 at 09:51 PM.
07-21-2010, 08:09 PM   #28
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Fascinating read.

Falk, you referred to a "static offset" blur component. If I interpret your charts correctly, it looks to cause on the order of 1px blur. Any thoughts as to it's origin?

Also, did you make any measurements with the camera in portrait orientation? One would expect the extraneous blur component to be midway between the 0 degree and 180 degree results, no?
07-21-2010, 08:24 PM   #29
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Interesting work. I am amazed that there isn't more of this kind of publicly available research on camera technology, and am grateful to you for doing this.

I wonder what other cameras use that Copal shutter? I imagine it is probably present in a few bodies from several camera manufacturers.

I also think this issue can't be that new. Fast, powerful Copal and other brand shutters have been around for a long time. Wouldn't it also have been present in the film days?
07-21-2010, 10:09 PM   #30
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QuoteOriginally posted by falconeye Quote
We discussed the issue with Pentax first. It helps everybody.

Executive level manager, both acknowledging the problem and appreciating our work. One of the problems is that it may be a rare case where technical information flows in the "wrong" direction. They are working at that
:standing ovation:

So this is what you referred to in your SR article comment?

I don't see how this changes the observation that SR was ineffective above 1/100s? Unless your data was simply extrapolated from 1/100s.

Actually that rings a bell.
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