# CoC equivalent for motion blur?



## [dh] (Jan 11, 2013)

Hi all,

A bit of a theoretical question, rather than truly tech support... but figured this was the best place for it. I was thinking about whether there's some way of calculating minimum shutter speed for a moving camera or a moving object (or some combination of the two, obviously). When talking about depth-of-field, the circle of confusion (CoC) is used to quantify pixels in the image which are 'acceptably sharp'. 

Is there any equivalent concept for motion blur -- i.e., how many pixels an object can move in-frame and still be considered 'frozen' or 'sharp'? It seems like the CoC measure should apply equally (i.e., CoC tells us what the maximum blurriness of a spot on the image that is still perceived as sharp), since we're still talking about blur, just from a different source (motion vs. aperture). Does it make sense to apply the same concept to motion blur, or am I way off base?

Thanks,
-dh


----------



## [dh] (Jan 11, 2013)

Doing some more digging, it seems like there's at least (old) precedent for this. 

From Wikipedia:
The common 1/100 inch COC limit has been applied to blur other than defocus blur. For example, Wall (1889, 92) says:
_"To find how quickly a shutter must act to take an object in motion that there may be a circle of confusion less than 1/100in. in diameter, divide the distance of the object by 100 times the focus of the lens, and divide the rapidity of motion of object in inches per second by the results, when you have the longest duration of exposure in fraction of a second."_
http://en.wikipedia.org/wiki/Circle_of_confusion_diameter_limit#Wall_1889

Would still appreciate any insight that others may have into this, FWIW.

Thanks,
-dh


----------

