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12-10-2010, 08:54 AM   #16
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QuoteOriginally posted by Class A Quote
The SR mechanism can only compensate for rotational motion. Pentax cameras don't have sensors for translational shake.
AFAIK This was an old translation error. They only compensate for translational, until the K-7 (K20D?), which added rotational.

12-10-2010, 09:07 AM   #17
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Long article from Falk Lumo:
Falk Lumo: Pentax shake reduction revisited

Conclusion: SR only kicks in below 1/50 so they claim long lenses at high shutter speed don't benefit from Pentax SR.

Bob Atkins article:
How Slow can you HandHold a Camera

Class A is right, I reversed the two cases.

Bob points out that translation is insignificant at long ranges, so only rotation correction is required, however at macro distances, translation is VERY important, and only Canon corrects for this (with their new hybrid IS in the 100/2.8L IS USM macro).

I would assume that the K-7 added correction for translation (just as the new Canon macro has).
12-10-2010, 09:29 AM   #18
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QuoteOriginally posted by JHD Quote
Wow! That's exceptionally amazing... 300mm x 1.7 = 510mm @ 1/40th. That's about 3.5 stops, no?
closer to 4 stops, but this again is against the rule of thumb. I think the results of SR really depend upon the technique used and skill level. Clearly someone with no experience hand holding a long lens, using bad technique, or perhaps thinking they can properly aim a camera using live view with a 500mm lens, will never achieve anything like this.

SR is NOT a fix all for technique, but the shot I posted shows what SR and good technique can do. I am quite certain that I could not have held this shot without SR, and I an not sure what the minimal shutter speed I could have used would have been to get this shot without SR, or even if this shot would have been possible.

This was taken at dusk, at ISO1600 and about F5.6 (set on the lens) or F10 effictive aperture (to get enough DOF for the bird) at the shooting distance

If the shutter speed had to be bumped up for hand holding, without SR this shot simply would not have been possible.

Similairly, except for a few species of birds that actually sit still, while SR makes shots like this possible, AMY subject movement would have made the shot impossible.

SR is NOT a substitute in all cases for faster lenses.
12-10-2010, 09:52 AM   #19
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Part of that good technique people talk about must be don't drink too much coffee.

12-10-2010, 11:25 AM   #20
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QuoteOriginally posted by JHD Quote
Part of that good technique people talk about must be don't drink too much coffee.
I drink between 3-4mugs (8-12 cups) per day, I guess that this is not too much
12-10-2010, 04:17 PM   #21
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QuoteOriginally posted by Eruditass Quote
AFAIK This was an old translation error. They only compensate for translational, until the K-7 (K20D?), which added rotational.
The "translation error" was to claim "roll" compensation for cameras before the K-7. Personally, I don't believe in that story. Perhaps it was unintended advertising first but there was plenty of opportunity to put the facts right. However this never happened. Only when the K-7 needed to claim it as a new feature, older DSLRs were suddenly robbed of the feature.

All Pentax DSLRs with SR before the K-7 only compensated for "yaw" and "pitch" rotational shake. No Pentax DSLR will compensate for any translational shake you may expose it to. This is not a problem as rotational shake dominates image blur unless you enter the macro realm.

P.S.: Only "roll" motion is countered by rotating the sensor. The "yaw" and "pitch" motions are countered by shifting the sensor within its 2D plane. The latter may suggest that translational shake is compensated but this is not the case.

Last edited by Class A; 12-10-2010 at 04:23 PM.
12-11-2010, 05:55 AM   #22
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QuoteOriginally posted by orly_andico Quote
Long article from Falk Lumo:
Falk Lumo: Pentax shake reduction revisited

Conclusion: SR only kicks in below 1/50 so they claim long lenses at high shutter speed don't benefit from Pentax SR.
That conclusion is not right. Personally I believe Falk was tricked by the shutter blur issue and then extrapolated the result a bit to far without actually testing it. But I also believe/hope he will do a new test in the future.
12-11-2010, 06:51 AM   #23
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QuoteQuote:
Does SR's effective diminish with focal length?
Yes.

Its effect is to counter camera pitch or yaw by pitching or yawing the sensor in the opposite direction to compensate for image motion on the sensor.

For a given rate of pitch or yaw, image motion on the sensor is directly proportional to lens focal length (double the focal length, double image motion); there is a limit to how far and how fast the camera can move the sensor, therefore there is a focal length above which the SR mechanism cannot keep up.

The critical focal length depends on how fast the lens pitching or yawing (ie, how steady the camera is being held). Roughly,

Max_focal_length = (SR_Constant)*(Circle_of_Confusion)/ (Yaw_or_Pitch_Rate*Exposure_Time)

Dave

12-11-2010, 07:06 AM   #24
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QuoteOriginally posted by newarts Quote
Yes.

Its effect is to counter camera pitch or yaw by pitching or yawing the sensor in the opposite direction to compensate for image motion on the sensor.

For a given rate of pitch or yaw, image motion on the sensor is directly proportional to lens focal length (double the focal length, double image motion); there is a limit to how far and how fast the camera can move the sensor, therefore there is a focal length above which the SR mechanism cannot keep up.

The critical focal length depends on how fast the lens pitching or yawing (ie, how steady the camera is being held). Roughly,

Max_focal_length = (SR_Constant)*(Circle_of_Confusion)/ (Yaw_or_Pitch_Rate*Exposure_Time)

Dave
Dave while this may apply to people with really bad technique, where the limits are hit at relitively short focal lengths, go back to my hand held post at 1.40th for a 510mm lens. If you have good technique SR remains effective even at extreme focal lengths, (I consider 500mm extreme).

Now the question is, can you hand hold a 1000mm lens at something in the range of 1/100? it will be really hard to tell beccause except for a mirror lens, no one can actually hand hold a 1000mm lens, they are just too big.
12-11-2010, 07:35 AM   #25
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QuoteOriginally posted by Lowell Goudge Quote
Dave while this may apply to people with really bad technique, where the limits are hit at relitively short focal lengths, go back to my hand held post at 1.40th for a 510mm lens. If you have good technique SR remains effective even at extreme focal lengths, (I consider 500mm extreme).

Now the question is, can you hand hold a 1000mm lens at something in the range of 1/100? it will be really hard to tell beccause except for a mirror lens, no one can actually hand hold a 1000mm lens, they are just too big.
Lowell, I'm not arguing with your technique example at all, just presenting some approximate physics that reinforces it.

Repeating the motion blur equation,

Max_focal_length = (SR_Constant)*(Circle_of_Confusion)/ (Yaw_or_Pitch_Rate*Exposure_Time)

The camera's pitch rate is in the denominator so as it approaches zero (by good hand-held technique, leaning on a tree, using a tripod, etc) the maximum lens focal length approaches infinity.

Dave
12-11-2010, 09:15 AM   #26
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QuoteOriginally posted by newarts Quote
Lowell, I'm not arguing with your technique example at all, just presenting some approximate physics that reinforces it.

Repeating the motion blur equation,

Max_focal_length = (SR_Constant)*(Circle_of_Confusion)/ (Yaw_or_Pitch_Rate*Exposure_Time)

The camera's pitch rate is in the denominator so as it approaches zero (by good hand-held technique, leaning on a tree, using a tripod, etc) the maximum lens focal length approaches infinity.

Dave
No argument there, I think the way to express it mathematically would be to add a constant for technique, because as you say in words, as technique improves, maximum focal length approaches infinity.

Maybe the constant is a function of each persons own performance i.e. focal length* shutter speed (in seconds) so that if I can hand hold a 500mm lens in 1/500 the constant is 1, if I can hand hold it in 1/250 the constant is 2 etc. this way, technique comes into the equation directly. no one will have an infinite focal length because that implies they don't need SR at all, which is what a tripod achieves
12-11-2010, 11:09 AM   #27
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QuoteOriginally posted by Lowell Goudge Quote
No argument there, I think the way to express it mathematically would be to add a constant for technique, because as you say in words, as technique improves, maximum focal length approaches infinity.

Maybe the constant is a function of each persons own performance i.e. focal length* shutter speed (in seconds) so that if I can hand hold a 500mm lens in 1/500 the constant is 1, if I can hand hold it in 1/250 the constant is 2 etc. this way, technique comes into the equation directly. no one will have an infinite focal length because that implies they don't need SR at all, which is what a tripod achieves
The "SR_Constant" term in the equation was intended to cover the camera's Shake Reduction function. The person's holding ability is in the "yaw_rate" variable on the bottom.

I'll try to rewrite things in a more intutive fashion.

Dave
12-12-2010, 06:20 AM   #28
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QuoteOriginally posted by Lowell Goudge Quote

Maybe the constant is a function of each persons own performance i.e. focal length* shutter speed (in seconds) so that if I can hand hold a 500mm lens in 1/500 the constant is 1, if I can hand hold it in 1/250 the constant is 2 etc. this way, technique comes into the equation directly. no one will have an infinite focal length because that implies they don't need SR at all, which is what a tripod achieves
Perhaps it is best to follow your example and use words and stops to describe the situation:

The average person can hand-hold a manual camera according to the old rule of thumb:

Shutter_speed ~ focal_length which can be modified as follows:
- an individual's skill in holding the camera steady can add (or subtract) speed stops.
- a camera's or lens' Shake Reduction function can add a few speed stops.
- enlarging an image 2x subtracts one speed stop.

This is the same as:

Shutter_speed ~ Focal_length*Enlargement/(Individual_skill*Camera_shake_reduction)
where Individual_skill = 1, 2, 3, etc., Camera_shake_reduction= 1(off), 3(on), Enlargement=1, 2, etc.

Dave
12-12-2010, 07:27 AM   #29
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SR's effectiveness isn't constant but it doesn't diminish with focal length.

This is what I posted earlier this month:
https://www.pentaxforums.com/forums/1288451-post4.html


QuoteOriginally posted by Gimbal Quote
That conclusion is not right. Personally I believe Falk was tricked by the shutter blur issue and then extrapolated the result a bit to far without actually testing it. But I also believe/hope he will do a new test in the future.
Gimbal is correct. I said so in the comments section of that article too. However, I relied on third party test data at 200mm (Colorfoto) too... I will pull this blog post as soon as I find time to redo it for the K-5. I already have the measurements for the K-7 and they have been published here:
[IMGWIDELEFT]http://www.falklumo.com/lumolabs/articles/k7shutter/images/extrablur.png[/IMGWIDELEFT]
http://www.falklumo.com/lumolabs/articles/k7shutter/images/extrablur.png

In summary:

While the sweet spot of Pentax SR may be around 1/15s, it works at 1/200s or 1/500s too.
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