Image Stabilisation

[klindup]

It is now almost a month since there were any new postings to this forum so for the benefit of those of us who miss activity I pose a question.  Given the improvements in noise levels at higher ISO settings that mean that we can use higher shutter speeds; do we still need image stabilisation in our lenses?  Are there any downsides to image stabilisation apart from cost?

Ken Lindup

[KeithB]

Any time you introduce a new element, there is going to be some image degradation, but one can only hope that Canon keeps that to a minimum.

I think IS still has value, because while ISO is improving, the zoom lenses we seem to like are pretty slow. If you shoot fast primes, it is a different story.

[Frank Kolwicz]

First, as an addendum to Keith's remarks "If you shoot fast primes (. . .), it is a different story.", I have to add ". . . wide open" where I inserted the parentheses.

I shoot what should qualify as a fast prime, Canon 600/4 (fast for it's type, certainly), on a tripod or window mount and almost always use f/8 or smaller apertures. IS makes it possible to reliably use shutter speeds down to at least 1/50th sec. for birds at 20 feet where the subject allows. I have been able to use shutter speeds down to 1/125th occasionally without IS and at 20 feet, maybe double that would be practical, but not reliable.

Just for the hell of it one day, I hand-held my 600/4 (briefly and very wobbly!) while standing on a dock for an egret that landed practically in my lap (that is at the minimum focus distance) and got acceptable focus with speeds around 1/1000th. The image was very noticeably jumping around and I had trouble framing the bird, but it worked.

[Bob Atkins]

It's not always true that adding elements results in optical degradation. You can have too few elements as well as too many! If the lens is well designed, the moving group in an IS system is part of the overall lens design and so it's possible to have an IS lens that's just as good as a non-IS version. These days the IS groups are usually part of the lens design, not just extra elements added on to the back of a non-IS lens. In practice I don't think there is any real optical downside to IS. The only problem (and I've experienced it myself) is when you have the camera on a tripod and you are shooting at very slow speeds and forget to turn the IS off! In that situation the IS can cause a slow image drift which causes blur. Many of the larger lenses with IS will automatically turn IS off if they sense no movement, but that's not the case with all IS lenses (and none of the lower cost consumer IS lenses).

Whether it's useful on not on fast primes shot wide open depends on what you are shooting. There will always be times when even with a fast lens and high ISO you're at a shutter speed that's too low for handholding without IS. Alternatively IS may let you shoot at ISO 400 rather than ISO 3200 and so get an image with lower noise. Or it could allow you to shoot at f8 if you needed extra depth of field. Assuming of course you don't need a faster shutter speed to freeze action. So my take is that IS would be useful, even on a 50mm f1 lens. It's just that you'd probably need it less often than you would on a 50mm f2.8 and much less often than a zoom with a maximum aperture of f5.6 at 50mm.

The only real downside to IS is it adds some cost to the lens, though if Canon can put it in a $200 18-55 IS lens then the added cost of the simple IS system can't be much. IS also adds some complexity, i.e. it's one more thing that can break. That being said I don't remember hearing of many IS problems. Focus failures are rare, yet they are still much more common than IS failures. And even with failed IS you can probably still use the lens.