Why is image stabilisation making images unsharp?

Question

During vacations and travel I tend to use my Nikon D90 and a 18-200 VR (image stabilisation) lens.

I was very annoyed (and had no explanation) when I found images to be unsharp, which had be made in wide (20-30mm) and very fast shutter times (1/800s).

The images obviously had been unsharp from camera shake, but this was improbable if not impossible at 1/800s and 30mm using an VR/IS Lens.

Later someone told me he read somewhere in the internet that VR lenses tend to blur pictures at very short shutter speeds like mine.

I paid more attention to it, and my blur problems all are with VR lenses at very fast shutter speeds.

So I'd like to know: why to VR lenses blur pictures? At what speed do they ruin my pictures? Is there anything to do about this apart from disabling VR or better not buing lenses with VR/IS?

(interesting side note: as far as he told me only systems with VR/IS in the lens are prone to this problem. Systems with IS/VR in the DSLR Body do not have this problem).

Answer 1

Using lenses with IS can take a little practice to get used to and use effectively. There are times when IS/VR may actually add blur to your images, due to the way it functions. Generally, if you are using a lens with image stabilization, you need to make sure that IS is active and tracking before you fully press the shutter button. If you make the mistake of fully pressing the shutter from a fully depressed state, IS will kick in as the shot is being exposed, which results in either blur, or possibly a slight double-image. This can occur at any shutter speed, slow or fast, since it is the lens group inside the lens itself that is causing it when it moves once IS is activated.

The solution is to make sure you have the shutter button partially pressed when you are tracking and framing your shot. Use the IS feature to help you frame your shots hand-held, and when you have it framed, fully press the shutter without lifting your finger first. This will keep the IS active while the image is exposed, and only disable it after you depress the shutter button. If you are using a tripod, you may need to disable your IS/VR feature on the lens. Some lenses have tripod-sensing IS, or mutli-modal IS. If you have either of these, you should be ok to leave IS on while on a tripod, however it is best to take a couple trial shots to determine that for certain. If you have a modal IS feature, you may want to change the mode if there is a tripod-specific mode. If you have any blurring trouble while using an image-stabilized lens on a tripod, it is best to just disable it and go without IS. At times, you may find that you have trouble focusing a shot with a telephoto lens on a tripod, and that IS is the only thing that helps. I regularly enable IS to frame and focus, then disable it (carefully as to not change my composition) and use a cable-release to actually trigger the shot.

Answer 2

As it is when questions are burning me, I searched the web for more information about this and found a very good article by Thom Hogan explaining the Nikon VR system (and it's limits):

His findings explain my problems: he says to be careful with VR with shutterspeeds of 1/500s and below, since these are prone to problems since they come too close to the sampling rate of the VR system.
Due to the pitfalls of the VR system he recommends disabling VR if you don't need it.

The article is a very good read, it explains a lot of details of VR, the difference between normal and active VR, VR and the new VR II, how to use VR when panning or standing on a moving platform...