Open Photography Forums  
HOME FORUMS NEWS FAQ SEARCH

Go Back   Open Photography Forums > Digital Camera Discussion > Imaging Technology: Theory, Alternatives, Practice and Advances.

Imaging Technology: Theory, Alternatives, Practice and Advances. This is a brand independent discussion of theory, process or device. Ignore this forum unless this matters to you!

Reply
 
Thread Tools Display Modes
  #1  
Old January 27th, 2010, 08:42 AM
Doug Kerr Doug Kerr is offline
Senior Member
 
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,565
Default Camera shake

We are all aware of a hoary guideline regarding the choice of shutter speed to keep to an acceptable degree the "image smearing" caused by movement of the camera during the exposure.

The guideline, initially articulated in the context of full-frame 35-mm photography, suggests that:
With a lens of focal length f, the exposure time should be no greater than 1/f.
When we take into account the effect of image size on the matter, we can say that this guideline (for better or worse) can be restated as:
With a lens whose full-frame 35-mm equivalent focal length is f', the exposure time should be no greater than 1/f'.
We recognize that this guideline is very simplistic, and does not take into account any of the following:

Variations in the "steadiness" of the photographer.
The moment of inertia of the camera (which comes from its mass and its shape). [A camera with a higher moment of inertia will displace its pointing axis less in the hands of a given photographer.]
Our criterion for acceptable smearing of the image, including what fraction of the time will we attain it (given that the phenomenon is random).

So the guideline essentially adopts assumptions for all of those (although those are probably not stated anywhere - the guideline was adopted empirically).
[Before I proceed, let me note that here I will only deal with shake due to "angular" displacement of the camera axis; I do not deal with "translational" displacement, in which the camera shifts its position. This is in fact of practical consequence in the case of objects at a short distance. But here I exclude that situation.]
All that having been recognized, and accepted (since we don't really know how to take account of any of those), we need to recognize a further fundamental assumption of the guideline: that the degree of displacement of the camera's pointing axis (perhaps the standard deviation of that displacement, recognizing its random statistical nature) is proportional to the exposure time. We can recognize this in the guideline through the following train of thought:

We have a certain situation (with regard to the photographer, moment of inertia of the camera, and so forth). With a focal length of 100 mm, the guideline recommends a shutter speed no slower than 1/100 sec.

That means that the angular displacement of the axis that occurs during 1/100 sec shifts the image on the focal plane by an amount that we consider to be "just acceptable smearing".

If we then consider a focal length of 200 mm, because the distance from the second principal point to the focal plane is now twice what it was before (we assume focus at a substantial distance), that same angular displacement will now cause twice the shift of the image on the focal plane (representing twice the acceptable smearing).

To restore "just acceptable smearing", we must cut the shift of the image in half; thus we must cut the angular displacement in half.

If in fact displacement over the duration of the exposure is proportional to exposure time, we can do that by cutting the exposure time in half.

Since that is in fact how the guideline works, then we can reasonably say that it is predicated upon the fact that displacement over the duration of the exposure is proportional to exposure time.
[In fact, that relationship is intuitively a little hard to swallow. It essentially assumes movement of the camera axis in the same direction at a fixed rate for the entire duration of the exposure. It might apply if the camera was on a tripod which was falling over.]
Doubtless the major players in today's camera industry have recently developed well-founded, sophisticated models of camera shake behavior, in connection with their work on image stabilization systems. But I suspect that little of this has been published.

A recent article, though, by three "camera phone" researchers at Stanford University, reports their development of such a model, essentially "from the ground up". They needed to do this because:

The traditional guideline was not based on any real model at all.
Models developed of late by the "Tokyo club" have not been revealed.
Camera phones typically have dramatically lower moments of inertia than the cameras presumed by the traditional guideline.

The article is here:

http://scien.stanford.edu/jfsite/Pap...ameraShake.pdf

I will be reviewing it over the next little while, and will perhaps "publish" here my detailed observations.

One result, though, seemed worthy of reporting now. The work of this study showed that, rather than the amount of displacement of the camera axis during the exposure (actually, the standard deviation of the instantaneous displacement) being essentially directly proportional to the exposure time, it is actually essentially proportional to the exposure time to the 0.56 power.

The implication of this can be grasped from this numerical example:

If for a focal length of 100 mm, with a shutter speed of 1/100 sec (following the "guideline"), the smearing is in fact "just acceptable", then:
For a focal length of 200 mm, the "fastest" shutter speed to attain the same smearing criterion would need to be about 1/350 sec (not 1/200 sec, as produced by the "guideline").
For a focal length of 50 mm, the "fastest" shutter speed to attain the same smearing criterion would need to be about 1/30 sec (not 1/50 sec, as produced by the "guideline").

The article also has very interesting material on criteria for assessing image smearing, and how the pixel resolution of the camera impacts the perceptual implications of a certain degree of image shift. But that is beyond the scope of this note.

That's about it for now. Stay tuned.
Reply With Quote
  #2  
Old January 27th, 2010, 12:01 PM
Nicolas Claris Nicolas Claris is offline
Administrator/Moderator
 
Join Date: Apr 2006
Location: Bordeaux
Posts: 5,772
Default

Thanks Doug!

we all sing together for you: 'shake baby, shake!'
;-)
__________________
WEBSITE - FACEBOOK - INSTAGRAM
Please do no repost my images elsewhere than OPF without my permission.
Reply With Quote
  #3  
Old January 27th, 2010, 12:19 PM
Asher Kelman Asher Kelman is offline
OPF Owner/Editor-in-Chief
 
Join Date: Apr 2006
Posts: 34,782
Default

Quote:
Originally Posted by Doug_Kerr View Post

One result, though, seemed worthy of reporting now. The work of this study showed that, rather than the amount of displacement of the camera axis during the exposure (actually, the standard deviation of the instantaneous displacement) being essentially directly proportional to the exposure time, it is actually essentially proportional to the exposure time to the 0.56 power.

The implication of this can be grasped from this numerical example:

If for a focal length of 100 mm, with a shutter speed of 1/100 sec (following the "guideline"), the smearing is in fact "just acceptable", then:
For a focal length of 200 mm, the "fastest" shutter speed to attain the same smearing criterion would need to be about 1/350 sec (not 1/200 sec, as produced by the "guideline").
For a focal length of 50 mm, the "fastest" shutter speed to attain the same smearing criterion would need to be about 1/30 sec (not 1/50 sec, as produced by the "guideline").

The article also has very interesting material on criteria for assessing image smearing, and how the pixel resolution of the camera impacts the perceptual implications of a certain degree of image shift. But that is beyond the scope of this note.

That's about it for now. Stay tuned.
Then, Doug,

IF the conditions you have outlined for acceptable smear are in play, then, for an example, for a 70-200 mm 2.8L IS zoom, for example, very roughly, if one is satisfied with the anti-shake performance at 100 mm then one would go 3 times faster at least at 200 mm and 3 times faster at 70 mm.

IOW, anti-shake shouldn't be considered a fixed remedy for remedy of camera movement.

Another result could be suggested:


Stitching a night panorama:

If one has a "super-fine" lens and a "super-fine" sensor, for example a 24mm T/S II, (manual lens), on a 5DII, it might be better to hand hold at low speeds then a 50 mm manual lens in making a hand held panorama in low light where slower speeds are needed.

Asher
__________________
Follow us on Twitter at @opfweb

Our purpose is getting to an impressive photograph. So we encourage browsing and then feedback. Consider a link to your galleries annotated, C&C welcomed. Images posted within OPF are assumed to be for Comment & Critique, unless otherwise designated.

Last edited by Asher Kelman; January 27th, 2010 at 01:44 PM.
Reply With Quote
  #4  
Old January 27th, 2010, 01:17 PM
Doug Kerr Doug Kerr is offline
Senior Member
 
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,565
Default

Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post
IF the conditions you have outlined for acceptable smear are in play, then, for an example, for a 70-200 mm 2.8L IS zoom, for example, very roughly, if one is satisfied with the anti-shake performance at 100 mm then one would go 3 times faster at least at 200 mm
Well, none of this takes into account in any way, or has anything to do with, image stabilization features - do you mean with the IS off?

Then going from 100 mm to 200 mm, you should consider a shutter speed at least 3 times as fast; going from 100 mm to 70 mm, you could consider a shutter speed half as fast.

Best regards,

Doug
Reply With Quote
  #5  
Old January 27th, 2010, 01:49 PM
Asher Kelman Asher Kelman is offline
OPF Owner/Editor-in-Chief
 
Join Date: Apr 2006
Posts: 34,782
Default Here's the related but manual operation question

Hi Doug,

While we are dealing with keeping smearing degradation of images as low as we can in ordinary shooting conditions, the discussion you have instigated has implications on taking hand-held pictures. After all, out muscle systems are our own biological image stabilization system, (albeit imperfect).

My comment on manual focus is not for the IS off on the 70-20, rather to application of the sense of the matter to our shooting of panoramas in low light.

Quote:
Originally Posted by Asher Kelman View Post

Stitching a night panorama:

If one has a "super-fine" lens and a "super-fine" sensor, for example a 24mm T/S II, (manual lens), on a 5DII, it might be better to hand hold at low speeds then a 50 mm manual lens in making a hand held panorama in low light where slower speeds are needed.
__________________
Follow us on Twitter at @opfweb

Our purpose is getting to an impressive photograph. So we encourage browsing and then feedback. Consider a link to your galleries annotated, C&C welcomed. Images posted within OPF are assumed to be for Comment & Critique, unless otherwise designated.
Reply With Quote
  #6  
Old September 26th, 2010, 08:50 AM
Martin Evans Martin Evans is offline
Member
 
Join Date: Mar 2010
Location: East Anglia, England
Posts: 103
Default

A confused beginner's question: when is it a disadvantage to have a DSLR's 'antishake' 'image stabilizer' (or whatever the manufacturer labels it) turned on?
I ask this because I have seen the Pentax K-x criticised because it takes many clicks through the menu to turn the shake reduction function on or off, unlike other Pentax K models in which this function is controlled by a switch on the body.
Is there a cost in having the shake reduction always turned on, and if so when would one need to turn it off in a hurry?
Thanks,
Martin
Reply With Quote
  #7  
Old September 26th, 2010, 09:57 AM
Doug Kerr Doug Kerr is offline
Senior Member
 
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,565
Default

Hi, Martin,
Quote:
Originally Posted by Martin Evans View Post
A confused beginner's question: when is it a disadvantage to have a DSLR's 'antishake' 'image stabilizer' (or whatever the manufacturer labels it) turned on?
The main situation in which having the IS turned off used to be recommended is when the camera is on a tripod.

The servo system that compensates for lens axis motion, like many servo systems, may have a little bit of "hunt" in it (as a result of the designers wanting the fastest response). The amount of hunt is insignificant compared to the movement from camera "shake", so it is part of a good bargain.

But with the camera free of actual shake (as when on a tripod), then the small "hunt" adds blurring (a tiny bit) we otherwise wouldn't have, to no benefit. Thus the suggestion to turn IS off in that situation.

But many of the newer stabilized lenses (all the newer Canons) have logic that discerns when the camera is probably on a tripod (very little shake detected) and disables the servo (to dispose of the "hunting"). So turning the IS off is not really needed for such lenses.

Quote:
I ask this because I have seen the Pentax K-x criticised because it takes many clicks through the menu to turn the shake reduction function on or off, unlike other Pentax K models in which this function is controlled by a switch on the body.
If that body, like the Canon lenses I mentioned, is smart enough to disable the servo when it seems that the camera is on a tripod (I have no idea), then there would be rarely any need to turn IS off, and the fact that doing so was a little clumsy probably would not be a practical disadvantage.

Best regards,

Doug
Reply With Quote
  #8  
Old September 27th, 2010, 05:05 AM
Martin Evans Martin Evans is offline
Member
 
Join Date: Mar 2010
Location: East Anglia, England
Posts: 103
Default

Many thanks, Doug, for that very clear explanation.

Do you know what physical principle is used to detect camera shake? Does the system sense an inertial movement, or is instability of the optical image sensed?

I can see that in the case of a camera that is designed to be inexpensive, such as the Pentax K-x, it would be cheaper to enable/disable a function through software rather than through a separate hardwired switch. Especially if the switch etc was to be of professional quality, with gold-flashed contacts and stainless steel spring. Cheap switches often fail too soon.

Regards, Martin
Reply With Quote
  #9  
Old September 27th, 2010, 05:51 AM
Bart_van_der_Wolf Bart_van_der_Wolf is offline
pro member
 
Join Date: Jun 2006
Location: Netherlands
Posts: 4,054
Default

Quote:
Originally Posted by Martin Evans View Post
Do you know what physical principle is used to detect camera shake? Does the system sense an inertial movement, or is instability of the optical image sensed?
Hi Martin,

Detection is most likely all electronic, with accelerometers. Soft/firmware would be too slow if an optical image needs to be analysed first. From there on there is firmware involved to take corrective action.

Cheers,
Bart
Reply With Quote
  #10  
Old September 27th, 2010, 07:27 AM
Nill Toulme Nill Toulme is offline
Senior Member
 
Join Date: Jun 2006
Location: Atlanta, Georgia USA
Posts: 1,407
Default

As I recall, another important assumption that went into the formulation of the hoary old guideline was image size and viewing distance. I believe that guideline assumed a print size of no larger than 8x10, viewed at "normal" distance.

Larger prints and closer viewing dictate more rigor with regard to avoiding camera shake. This point has become all the more important in these troubled times of viewing 18MP images at 100% pixel size on 30" monitors...

Nill
Reply With Quote
  #11  
Old September 27th, 2010, 07:35 AM
Doug Kerr Doug Kerr is offline
Senior Member
 
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,565
Default

Quote:
Originally Posted by Martin Evans View Post
Many thanks, Doug, for that very clear explanation.

Do you know what physical principle is used to detect camera shake? Does the system sense an inertial movement, or is instability of the optical image sensed?
In most of the systems used in dSLRS, angular motion of the camera axis is detected (in the body or in the lens) with vibrating fiber gyroscopes. There do not have a rotating wheel, but rather a vibrating fiber. (During each half of its vibration cycle, it actually "rotates" about its fixed end, and then "rotates" the opposite way during the "back stroke".) Flies use a similar mechanism (halteres) for attitude control!

If there is angular movement, there is a "precession" force on the fiber (just as there would be on the wheel axis of a traditional gyroscope), which deflects the fiber, and that deflection is detected as its indication.

Some of the new Canon macro lenses detect (and correct for) both angular motion and "translational" motion (where the camera moves from side to side but without change in pointing angle - this can be consequential for work at close distances). I would assume that these might have both gyroscopes and accelerometers, although it probably could be done with two sets of accelerometers at opposite ends of the lens barrel.

I think that in some "compact" cameras this might be done by analysis of apparent motion of the image on the sensor, but I'm not sure.

Quote:
I can see that in the case of a camera that is designed to be inexpensive, such as the Pentax K-x, it would be cheaper to enable/disable a function through software rather than through a separate hardwired switch. Especially if the switch etc was to be of professional quality, with gold-flashed contacts and stainless steel spring. Cheap switches often fail too soon.
I think that is often a design consideration.

Best regards,

Doug
Reply With Quote
  #12  
Old February 20th, 2012, 06:50 AM
Adrian Wareham Adrian Wareham is offline
Member
 
Join Date: Jan 2012
Posts: 153
Default

An interesting read: http://en.wikipedia.org/wiki/Image_stabilization

Pentax, from what I read, moves the image sensor to compensate. Huh.

Anyway, reliability isn't a problem for most of the optical IS methods as most use Micro Electro-Mechanical Systems, so the sensor functions like many insects, but is entirely solid state. It appears the Canon-like sensors also don't "move" in quite that sense, but instead, are forced by the motion into a more energetic mode of vibration which, when brought back down to base, gives a measurable value for the energy gained, thus telling it exactly how much it was accelerated and in what direction on its plane.

-Adrian
Reply With Quote
  #13  
Old February 20th, 2012, 10:26 AM
Jerome Marot Jerome Marot is offline
Senior Member
 
Join Date: Jan 2011
Location: Munich, Germany.
Posts: 3,789
Default

Quote:
Originally Posted by Adrian Wareham View Post
Pentax, from what I read, moves the image sensor to compensate.
So do Sony (ex Minolta) and Olympus. This systems have the obvious advantage that stabilization works with any lens and the dubious inconvenient that the viewfinder is not stabilized.
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are Off
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
review day 1 Frank Doorhof Leaf AFi 7 review and opinions - By Frank Doorhof 11 October 2nd, 2012 08:33 PM
WB measurement from the camera position Doug Kerr CM Theory and Practice 4 November 3rd, 2009 11:17 AM
News: The Canon 7D is big news! Fast accurate focus and low light capability! Asher Kelman Breaking News 10 September 1st, 2009 10:09 AM
News: Camera that auto stitches and auto builds from multiple shots! Asher Kelman Breaking News 1 March 3rd, 2009 07:30 AM
The 50 D is here...where's the 5dMk2???? Kathy Rappaport Breaking News 30 August 28th, 2008 09:40 AM


All times are GMT -7. The time now is 07:32 AM.


Posting images or text grants license to OPF, yet of such remain with its creator. Still, all assembled discussion 2006-2017 Asher Kelman (all rights reserved) Posts with new theme or unusual image might be moved/copied to a new thread!