A sudy of the effectiveness of the K7 Shake Reduction


labnut

Link Posted 24/02/2010 - 12:08
Hi,
I know from the many posts there has been concern about the effectiveness of Pentax's Shake Reduction.

Like a lot of people I started to worry if I had a problem with my own camera.

My photos looked OK but still I wasn't sure. So eventually I decided to accurately measure the effectiveness of Shake Reduction in my K7. The project just grew and grew until in the end I had completed a large study.

The net result? Shake reduction in my K7 is very effective.

I would like to share the results of this study. You can find my report (pdf) at the following link(scribd.com):
Study of the Effectiveness of Shake Reduction in the Pentax K7
The main findings can be seen in the two graphs below, but see the report for more information
I welcome your comments. suggestions, critiques and ideas for improvements.




ChrisA

Link Posted 24/02/2010 - 12:32
A very warm welcome to the forum from me.

It's a great pleasure to see a careful look at a subject that, if you've been following the debates about SR here, you may know is quite close to my heart, not least because of all the shockingly bad science and anecdotal non-evidence that abounds and shapes people's views so easily.

I note your broad conclusions with interest, and when I get a chance, I'll read it in detail.

My particular hobby-horse, which I investigated for myself some time ago with the K10D, is the assertion from numerous quarters that the absence of shake itself causes the SR circuitry to cause unwanted sensor movement during the exposure.

I found no evidence of this in my experiments, which were nowhere near as quantitative as yours, but nevertheless careful.

I'd be interested in your comments on this.
.
Pentax K-3, DA18-135, DA35 F2.4, DA17-70, DA55-300, FA28-200, A50 F1.7, A100 F4 Macro, A400 F5.6, Sigma 10-20 EXDC, 50-500 F4.5-6.3 APO DG OS Samsung flash SEF-54PZF(x2)
.
Last Edited by ChrisA on 24/02/2010 - 12:34

labnut

Link Posted 24/02/2010 - 13:01
Thanks Chris. Yes I know that it is commonly asserted that SR should be off when mounted on a tripod. My tests were not mounted on a tripod but with the camera firmly clamped to a heavy workbench. Now I believed that assertion until I did my tests which show identical results between SR On and SR Off when clamped to a workbench.

See the graph below where I investigate this at 1/80 sec. Measured in the vertical direction image blur was 1.32 pixel with SR both on and Off. In the horizontal direction it was 1.26 and 1.29 pixel; a difference within measurement error.
By the way, I started out using a normal tripod but soon discarded that as my measurements showed a lot of residual movement in the tripod. The only way I could get a truly motionless camera was to clamp it firmly to a heavy workbench.

In the graph below I was looking for evidence of sensor vibration caused by mirror slap and concluded that it was no more than 0.21 pixel.

I should add that others have since pointed out to me that using a 50 mm lens is testing the K7 under favourable conditions and that I should use longer focal length lenses to subject the K7 to a more stringent test.


alun

Link Posted 24/02/2010 - 13:16
An impressive study.
However, if I understand your test correctly, is a camera 'firmly clamped to a heavy workbench' going to replicate what happens when the camera is on the relatively flimsy tripod? Afterall, would not a well fixed camera resist a sgnificant of external movement, let alone that generated by the movement of the internal sensor?

labnut

Link Posted 24/02/2010 - 13:27
Thanks Alun. With the bench mounted camera I was trying to get a really motionless camera where I could measure image blur free from added motion blur. This I called static blur (which is caused by resolution limits in the lens and sensor).

Then I conducted measurements with the hand held camera, again measuring image blur (with SR On and Off).

Now I could calculate motion blur by subtracting static blur from the image blur. This then gave me motion blur for both SR On and SR Off, allowing me to gauge how effective shake reduction really is.

alun

Link Posted 24/02/2010 - 13:59
OK labnut, thanks for the clarification. The bench mounted camera supplied your 'control' readings?

iceblinker

Link Posted 24/02/2010 - 14:18
So I take it that this test is not relevant to the argument about whether it is advantagous to turn off SR for tripod photography. It doesn't test the difference between the effects of SR with human shake and tripod vibration.
~Pete

labnut

Link Posted 24/02/2010 - 18:21
Alun, yes, the bench mounted readings were the control or reference set.
Pete,no it doesn't test the effects of SR with tripod vibration. Once could argue that if it made no difference with the bench mounted camera that similarly it would make no difference with the tripod mounted camera. But I suspect it is not as simple as that. For one, the bench mounted camera was very nearly motionless so the output of the motion sensors would be effectively zero. While I found I could always measure movement on the tripod mounted camera. This is what led me to abandon using a tripod and use the more extreme measure of really clamping the camera down on a work bench.

To understand this we really need to know more about how the circuitry works. It is rumoured that Pentax use the Murata Gyrostar angular motion piezoelectric gyroscope sensors. They seem straight forward enough, can sense angular velocity of up to 300 deg/sec and have a bandwidth of 0 to 50 Hz but are subject to temperature drift. But there is nothing in that which might suggest an answer. I can only think it is a damping problem. The control circuitry must be very sensitive to respond to hand movement but this makes it under damped when dealing with slower, lower amplitude movements on a tripod. At best I can describe my thoughts as uninformed speculation.

But I will test this.

imagesteve

Link Posted 24/02/2010 - 18:29
I am impressed with the effort of this study... very informative!
2x K10D bodies, 2x FA 28-200 3.8-5.6, DA 18-55, A 50 F2, 50mm Macro, 360 FGZ. Still saving for the 60-250 DA* Also have a Z10 35mm and a K1000 just for fun. IF PENTAX IS THE ANSWER, WHO CARES WHAT THE QUESTION IS...!
Quote:

robbie_d

Link Posted 24/02/2010 - 18:34
An interesting read, thanks for posting.
If you can't say something nice about Pentax, you won't say anything at all.

Apparently.

steveandthedogs

Link Posted 25/02/2010 - 08:42
An excellent study, well thought out and designed. SR is more effective than I realised, especially in the very low light situations.

labnut

Link Posted 25/02/2010 - 12:38
steveandthedogs wrote:
An excellent study, well thought out and designed. SR is more effective than I realised, especially in the very low light situations.

Thanks. After the many critical comments one sees about Pentax Shake Reduction it came as a surprise to see quite how effective it is. Though I should add this was done with a 50 mm lens and the picture may be different with a longer focal length lens. But I am going to test that.

I am attaching some links to key patents about Pentax's shake reduction technology.
They help to understand how it works.

Pentax-Shake-Reduction-Patent-Original-US7224893
Pentax-Shake-Reduction-Patent-7224893-Full-Text
Pentax-Shake-Reduction-Patent-20080226276-Full-Text
Pentax-Shake-Reduction-Patent-20080226276-Original

RichardDay

Link Posted 25/02/2010 - 12:56
Thank you for a very interesting and thorough study.

Have you posted this on the other "main" forums?
Best regards
Richard Day

Profile - link - (click on About for equipment profile) - My Flickr site - link

Greytop

Link Posted 25/02/2010 - 14:02
Very interesting Labnut, thank you for sharing, it certainly seems to correspond with my experience of Pentax SR which is very positive.
Using my K-7 I find it's quite possible to achieve consistently sharp shots below 1/10 second, even as low as 1/5 - 1/6 second with a little practice. This is generally with my 16-50 zoom walk around lens.
Regards Huw

flickr

Anvh

Link Posted 25/02/2010 - 14:46
labnut great study you've done here, you should try get some members so crazy to fund one of the new Sigma lenses with SR in the lens for you to compare if the SR in the lens is more effective or not
Stefan


K10D, K5
DA* 16-50, DA* 50-135, D-FA 100 Macro, DA 40 Ltd, DA 18-55
AF-540FGZ
Last Edited by Anvh on 25/02/2010 - 14:46
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