03-19-2015, 04:32 AM
IS works pretty "simply." Some physical method controls the position of the IS unit - be it an EM field, actuators, etc. All brands have different patents (well, sigma stole OS from Nikon VR, so they mostly have all unique methods) that give them rights to do it differently.
When the IS unit is initialized, it centers the IS group. Then a gyro collects movement data for frequencies between some range (canon IS is about 0.5Hz to 20hz) and initializes the movement in the opposite direction.
Traditionally the section of the lens that has the largest "sectional focal length" (i.e does not focus or diverge light or does this to a minimum) has been selected to turn into an IS unit, as the beam of light traveling through the lens will move the least if that section is disturbed. Those sections are also usually fairly stable re: aberrations, so it make sense. Recently canon developed an afocal IS unit, so it may be dropped into any optical system that can accommodate its size.
The IS unit may rest centered, or not. Depends how it is held. Often in optics spring tension systems are used to hold things still, so it is possible the IS unit is suspended in a net of springs that hold it very close to centered, and then it can measure the EM field to find the exact center and will move there upon initialization.
When the IS unit is initialized, it centers the IS group. Then a gyro collects movement data for frequencies between some range (canon IS is about 0.5Hz to 20hz) and initializes the movement in the opposite direction.
Traditionally the section of the lens that has the largest "sectional focal length" (i.e does not focus or diverge light or does this to a minimum) has been selected to turn into an IS unit, as the beam of light traveling through the lens will move the least if that section is disturbed. Those sections are also usually fairly stable re: aberrations, so it make sense. Recently canon developed an afocal IS unit, so it may be dropped into any optical system that can accommodate its size.
The IS unit may rest centered, or not. Depends how it is held. Often in optics spring tension systems are used to hold things still, so it is possible the IS unit is suspended in a net of springs that hold it very close to centered, and then it can measure the EM field to find the exact center and will move there upon initialization.