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11-29-2010, 03:31 PM   #1
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Does Pentax sensor-based Shake Reduction produce image distortion?

Hi Everyone,

This is a question that i have been pondering for sometime now.

To me, it seems that if you change the plane of the sensor relative to the lens elements, you will introduce distortion to the image. Much like the keystone effect on data projectors (except much less pronounced of course!). Is this so? If so, how much distortion would be generated in the worst-case scenario? Is it noticeable / detectable? If we want the truest images, should we be turning off SR?

11-29-2010, 03:42 PM - 1 Like   #2
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No, there is no induced distortion. The sensor moves side to side only (or rotates on the K5 as well) so that the sensor is always in the plane of focus. I only turn off my shake reduction when I am on tripod, where the sensor may attempt to correct non existent movement and create some on its own.
11-29-2010, 03:53 PM   #3
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I'm sure it would be reported and debated to death if true.
11-29-2010, 03:56 PM   #4
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as canadian rockies said, the motions are all in the same plane as the focus, therefore no distortion,

THis is one of the failings of ALL image stabilization techniques, they only work in X and Y dimensions, not the Z axis or toward / away from the sibject.

However, lens based Image Stabilization probably does introduce some odd off senter distortion because there the camera is only moving some elements. I am not sure if anyone has looked into this.

11-29-2010, 04:11 PM   #5
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Thanks for the clarification. I thought the SR mechanism pivoted on the centre point of the sensor.

But even if there is only sidewards motion, the angle of light hitting the sensor will change slightly, won't it? Not as much as if the sensor pivoted from the centre though. I'm inclined to think that it would be negligible in this case though.

I am still curious to know whether anyone has tried to measure it.
11-29-2010, 04:25 PM   #6
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I would guess that very strictly speaking there should be an insignificant amount of distortion akin to using a perspective correction lens? OTOH moving an element/group in the lens as OS does has a similar effect in that it moves the projected image relative to the sensor (it also decenters the optics as mentioned causing further distortion). Here "distortion" is used in a general sense, not as a synonym to barrel/pincushion distortion.
11-29-2010, 05:00 PM   #7
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It doesn't, but do make sure the SR system is armed before shooting (presence of the hand icon).

Be a judge of how effective the system is yourself: Pentax K-5 Review | PentaxForums.com

4 stops is not an overstatement.

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11-29-2010, 05:18 PM   #8
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I would agree 4 stops is reasonable

I have posted this before shot with 300mmF4 and 1.7x AF TC for 510mm focal lenght, at 1/40 hand held

this is a 100% crop, the Night heron filled almost the entire frame of my K7



11-30-2010, 02:42 AM   #9
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QuoteOriginally posted by Lowell Goudge Quote
THis is one of the failings of ALL image stabilization techniques, they only work in X and Y dimensions, not the Z axis or toward / away from the sibject.
The K-7 & K-5 do stabilise against camera rotation in all three axes.

The Pentax sensor-based shake reduction doesn't address camera translation. That's fine for non-macro photography. I reckon the problem is not the stabilisation method -- sensor shifting should be ideal for countering translational shake -- but the fact that Pentax cameras lack the sensor to detect translational shake.

There are macro lenses whose stabilisation system is optimised for macro work so I guess it tries to counter translation-induced shake (as opposed to rotation-induced shake).


QuoteOriginally posted by jolepp Quote
I would guess that very strictly speaking there should be an insignificant amount of distortion akin to using a perspective correction lens?
Yes, there should be a (minute?!?) amount of a "shift" effect, as desired in tilt & shift lenses. I'd say it is negligible but I haven't done the math.
11-30-2010, 10:02 AM   #10
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QuoteOriginally posted by Class A Quote
The K-7 & K-5 do stabilise against camera rotation in all three axes.
I believe you will find that this does not address any movement in the Z axis (nearer to/further from the subject), but rather offsets not only left/right movement and up/down movement in the sensor plane but also corrects for rotation, but still in the sensor plane (left hand goes up, right hand goes down) and does not correct for to/from movement.
QuoteQuote:
The Pentax sensor-based shake reduction doesn't address camera translation. That's fine for non-macro photography. I reckon the problem is not the stabilisation method -- sensor shifting should be ideal for countering translational shake -- but the fact that Pentax cameras lack the sensor to detect translational shake.

There are macro lenses whose stabilisation system is optimised for macro work so I guess it tries to counter translation-induced shake (as opposed to rotation-induced shake).

Yes, there should be a (minute?!?) amount of a "shift" effect, as desired in tilt & shift lenses. I'd say it is negligible but I haven't done the math.
12-01-2010, 11:21 PM - 1 Like   #11
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Missing Posts

We seem to have lost Class A's reply, and my subsequent compliment - thanks to the server switchover, no doubt. I hope Class A will revisit this thread...
12-02-2010, 02:25 AM - 1 Like   #12
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QuoteOriginally posted by m42man Quote
I hope Class A will revisit this thread...
Thanks a lot for the original compliment and the invitation to repost.

QuoteOriginally posted by Canada_Rockies Quote
I believe you will find that this does not address any movement in the Z axis (nearer to/further from the subject)...
One has to distinguish between rotational movement (yaw, pitch, roll) and translational movement (left/right, up/down, forward/backward).

The K-7/K-5 only has sensors for rotational movement. That's fine because at larger distances camera shake that is of rotational nature will dominate image blur. Think of a light point painted by a laser pointer on a distant wall. Any yaw and pitch movement will be very visible whereas any translational movement will be negligible in comparison.

Yaw and pitch rotational shake will be compensated by shifting the sensor within its plane (compensating the shift of the image -> think of the shift of the dot painted by the laser pointer on the far away wall) and roll rotational shake will be compensated via rotating the sensor in its plane.

For macro work there is a different story. Here the translational shake dominates and Pentax cameras cannot compensate for it because they don't have sensors for detecting translational shake.

There are a few lens-stabilisation systems for macro lenses which are optimised for close focus distances. I'm assuming such lenses can sense translational shake. It would be great if future Pentax cameras were fitted with further sensors so that SR would be useful for macro work as well.
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