Optical illusion or what? Re- IS

[Nathaniel]

I find that I appear to get sharper images with the IS turned off on my 70-300 L lens when shooting at speeds of say 1/1250 & above. Therefore do members recommend me to continue to turn off IS when shooting at those speeds?

Many thanks

Nat

[El Sid]

Re: Optical illusion or what? Re- IS

At that kind of speed I'd be doubtful that the IS has any effect regardless of whether it's on or not. At speeds above 1/1000th a vibration would need to be very fast and quite strong to cause any softening. My feeling is that the high shutter speed is the reason the images are sharp rather than the lack of IS...

[Enigma]

Re: Optical illusion or what? Re- IS

I'm a little surprised that IS degrades your images but agree with El Sid regarding its impact above 1/1000. Unless using low shutter speed deliberately (prop blur / panning / water etc) then I always use aperture and ISO to give me as high a speed as possible. However, no rules so do whatever gives you the best results ...

[Nathaniel]

Re: Optical illusion or what? Re- IS

Thanks Nigel and Enigma. I posed my question as I had read somewhere that one should switch off IS when taking pics at fast shutter speeds as the IS could cause the image to be "soft". I don't know whether this is old wives tales or not.

[El Sid]

Re: Optical illusion or what? Re- IS

Thanks Nigel and Enigma. I posed my question as I had read somewhere that one should switch off IS when taking pics at fast shutter speeds as the IS could cause the image to be "soft". I don't know whether this is old wives tales or not.

Sounds like internet twaddle to me. There used to be an issue with IS mounted on tripods causing uncontrolled feedback that led to soft images but that's because the lens was actually too stable. Handheld even at high shutter speed the IS is still doing what it should even if it's not required. I suppose there's an outside chance that if the mechanism hasn't steadied there may be the outside possibility of image movement caused by the mechanism - even then I would expect a fast shutter speed to negate this plus the IS seems pretty fast to react, especially with L lenses.

[@imagesBV]

Re: Optical illusion or what? Re- IS

Hmmmm...I'm thinking that if IS is designed to look at multiple oscillations of movement (shake) then at high shutter speeds its probably not fast enough and works on only a partial oscillation which may cause it to malfunction. i.e if it has five whole up and down shake cycles to work on it knows what correction to apply....but with fast shutter speeds it will have less than a whole oscillation to work on and therefore gets it wrong.
I used to be an electronics engineer so I know that I think I know what Im talking about.

[El Sid]

Re: Optical illusion or what? Re- IS

But the IS works independently of the shutter and is activated when the shutter button is partially depressed. Granted it does take a short time to settle but even so I can't see how it could possibly be oscillating fast enough to cuase softening at high shutter speed - if it did then I can't see how it could possibly be effective at slow speeds...

[the black fox]

Re: Optical illusion or what? Re- IS

A typical example is myself today .lovely weather blue skies so I popped down the castle on the estuary over high tide .not much about so in the end I took practise shots of the ever present gull population ,camera was set at 1/2000th sec f8 auto ISO . 9 points a/f selected .on review most shots looked soft ,I even mulled over selling the lens and getting a lighter one .THEN the penny dropped check the focus points on screen .missed the focus on each shot that was soft .
Point of post it's often far to easy to blame our equipment when it's often user error behind it

[antoeknee]

Re: Optical illusion or what? Re- IS

Another point is that the IS steadies the image on the sensor allowing a greater degree of accuracy for the AF.

Seem to recall this was a much debated topic when IS was in its infancy and there seemed to be no conclusive proof.

Given the different modes available for IS these days I'm doubtful there is an issue.

[colin C]

Re: Optical illusion or what? Re- IS

so I know that I think I know what Im talking about.

Classic Brian.

I fall more into the "I don't know what I don't know" category!

[colin C]

Re: Optical illusion or what? Re- IS

My understanding is that IS uses two miniature gyroscopes, one to control Yaw and the other to control Pitch. They take a second or so to spin up and when they are at full spin, you can feel some slight inertia when you move the lens left or right, up or down. One IS mode operates both Gyros and the other mode cancels one Gyro, to allow for panning a subject. If you have ever played with a full size gyro, you will recall how the inertial effect slows down and dampens any movement, so you can appreciate how to an extent, it smooths out your bodies minute movements on the camera when using slow shutter speeds.

Early versions gave you an extra stop of slow shutter speed, but were sometimes confused when used in a stable environment, such as a tripod. Effectively it was fighting to control something that wasn't there and sometimes gave you an unsharp shot, even though it was on a tripod. I understand that the very latest version can provide up to four stops and embedded electronics can detect the stable environment and override the IS effect.

Having had lenses with first generation IS, I am disciplined into only using IS when the shutter speed available to me is below the reciprocal of the lens, e.g. 1/500sec for a 500mm lens, 1/200sec for a 200mm lens, etc. So even though I know that the latest versions are clever enough not to fight against something that isn't a problem, I don't see the point in using it when I don't need it.

There is often confusion regarding what IS will achieve. It will minimise camera shake to a greater or lesser extent, but will have no effect on subject movement. The shutter speed you require to freeze the action is the shutter speed you need.

Here is something I found on a Canon site on the net. It doesn't mention the Gyros etc, but the real world comparison is interesting.


Many camera lenses come with some kind of lens stabilization technology. It’s usually called something different by every camera manufacturer (e.g. Nikon calls it “vibration reduction” and Canon calls it “image stabilization”), but they all have the same goal: helping to stabilize your lens.
It works great for those times when you’re forced to hand-hold your camera, but you should always make sure to turn it off when your camera is on a tripod.
The stabilization technology works by unlocking part of your lens, which allows the lens to “correct” movements. But, when your camera is sitting still on a tripod, the stabilizer will often look for movement that isn’t there, resulting in a blurry photo.
To illustrate this, take a look at the two photos I shot below. For both shots, my camera was locked onto a stable tripod. In the image on the left, I had the lens stabilization turned OFF. And, then I simply turned it ON for the image on the right.

Both photos above were taken with the same camera, lens, and tripod. The camera’s position did not move between the shots, and the aperture/shutter speed/ISO also stayed the same. The only difference between the two photos is that lens stabilization was turned ON in the photo on the right.
Interestingly, as I shot more photos with the lens stabilization turned ON (and the camera still in the same position locked on a tripod), the images got sharper with each shot. So, it seems like this particular lens was able to “learn” that the camera was on a tripod. But, every lens works differently, so it’s not safe to assume ALL lens stabilization works like this.
Some lenses claim to have the ability to always detect when your camera is on a tripod (and it’ll turn off the stabilization automatically), but I wouldn’t recommend relying on that feature. I’m sure that detection isn’t always 100% accurate (just like your autofocus isn’t always 100% accurate).
Plus, image stabilization uses up your battery. So, keeping it turned off will let you take more photos or shoot more video on one charge.

Hope that helps.

[antoeknee]

Re: Optical illusion or what? Re- IS

For the most part I tend to switch off IS when using on a tripod (talking landscape work) and particularly for long exposures. As Colin mentions modern lenses are supposed to 'sense' when a tripod is in use but I've never tested this.

Of course there are times I then forget to turn back on and wonder why some images aren't as sharp as I'd expect!

[Nathaniel]

Re: Optical illusion or what? Re- IS

Thanks folks for all your good advice. I think I am better off switching off IS when I use high speed but to turn it on for slower shutter speeds such as for concert or church photos.

[@imagesBV]

Re: Optical illusion or what? Re- IS

Sounds like a sensible conclusion.

[antoeknee]

Re: Optical illusion or what? Re- IS

Not too sure myself. You might find he lack of a stable image in the viewfinder at longer focal lengths is an issue.

Can't say I've ever seen any evidence of an issue with IS and fast shutter speed. Some of my last kestrel images were at 1/1000 and 1/1500 and they were sharp.

This juv wren was at 1/1000 with IS and there is plenty of detail
Juv Wren by tblake2007, on Flickr