IS or not IS.

Discussion in 'Casual Photo Conversations' started by Nick D., Dec 12, 2017.

  1. The term, "spin up," may refer to a time early in the history of IS when Canon and Nikon used gyroscopes as accelerometers. Not only did it take time to bring them to speed, but they tend to precess, rendering the image somewhat unstable in the absence of motion. There were also "inertial" sensors which vibrated like tuning forks and were sensitive to motion outside the plane of vibration. Modern accelerometers are based on inertia of a fixed mass, measured by force transducers. These sensors are inherently stable and free from precession effects.
     
  2. How I wish for the option to automatically turn off VR when the shutter speed is faster than 1/focal length (or any other option I might choose like 1/2*focal length, 1/3*focal length, or a fixed shutter speed) and then engage again when the shutter speed becomes longer than that set point.

    I seem to recall having seen shots that had a weird background rendering allegedly caused by the VR working while using a "too fast" shutter speed (might even have been here on PN) but from what I recall it was not necessarily visible in every shot taken with the same set of parameters. More like a "bad luck" kind of thing.

    Nikon's various VR modes are poorly documented and one gains experience what works and what doesn't by trial and error. With some lenses, especially when panning with a relatively slow shutter speed of 1/125-1/200 when photographing propeller planes flying by, VR operation can cause a lot of images to be just slightly soft/blurry (of course, operator's lack of competence in panning just aggravates the issue).
     
    Last edited: Dec 20, 2017
  3. Ed, "spin up" is not a technical term, but it does accurately describe what I sense as my EF 500mm f/4L IS II USM gets ready for action. It's by no means instantaneous. If you mount the rig on a big, steady tripod (Arca-Swiss/Wimberley head and Induro's heaviest), then turn on the IS, you'll see momentary movement of the image and then stabilization. I'd guess the time from actuation to steadiness is 1/4 to 1/2-sec.
     
  4. Even if you use an accelerometer, there is noise in the data and the corrective action is affected by this noise. If the desire is for a more accurate reading of acceleration, this probably involves a longer reading time and so the corrective action is also delayed relative to the original movement. This kind of thing will never perfectly compensate all the shake, it involves a noisy measurement and some kind of prediction or estimation of what the optimal corrective action is. So on a tripod if you have a perfectly solid tripod it makes sense to turn VR/IS off. If the focal length is very long (say, 500mm or 800mm) then likely there will be enough vibration so that the correction is more beneficial than harmful. So it makes sense to use VR with such long focal lengths even on tripod. At least for exposure times that are not very long.
     
  5. I find this to be true with my Canon 500/f4 II. It's easy to see in the viewfinder.
     

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