When IS goes wrong

Mike Jackson

Mike Jackson

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Mike
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Forgot to turn the IS off for a low light shot earlier this evening and got a really graphic illustration of what it does to images.







 
Are these cropped images? Wow, didn't know it had that much effect (if those were taken using a tripod).
 
Never seen this before, funny shot isn't it. IS is amazing, still don't how it works.
 
100-400 L mounted on a tripod at 400mm f/8 5 secs 400 ISO IS mode 1. I assume the IS was trying to counteract the effect of the shutter.
 
albabbaobab said:
Are these cropped images? Wow, didn't know it had that much effect (if those were taken using a tripod).
Click to expand...

No cropping, I've never seen it have that much effect. I took 2 before I realised what I'd done. I assumed I'd knocked the tripod first time.
 
this could be why I kept ****in up with my BigmOS 150-500 on a tripod with OS on!

Dork:nono:
 
Just remembered - the other time I spotted it was using video on my 24-105 and 5DII.
It was on a tripod so should have been rock steady but on playback there was a subtle circular hunting movement that didn't stop until I turned off the IS.

As I said in my earlier post - with my combo you gotta be pixel peeping to spot this, but it's still there.
 
My 100-400L did that. It's got an older IS system without tripod sensing and you can get a feedback loop betwen the gyro and the motors when there's no movement actually happening.

You can see it in live view on max magnification. The image stays still most of the time, then it sometimes drifts very slowly before coming to its senses again.

I used still used to leave the IS on a lot of the time, as it's very effective at killing mirror slap at those critical speeds between about 1/20sec and 1/8sec or so that show it most. But longer than that you have to balance the reducing benefit with slap against the increasing likelihood of IS interference.

As a guess, I would say longer than 1/8sec, turn IS off for sure. Even better, turn it off anyway and use mirror lock-up, or live view, or some other form of damping the mirror vibration such as a weighty bean-bag resting on top, or a very careful hand just to kill the vibes. Tricky business.
 
Andy said:
Never seen this before, funny shot isn't it. IS is amazing, still don't how it works.
Click to expand...

Apparently IS works by floating the lens elements and counteracting any shake. If you put the lens up to your ear you can hear the bits and bobs inside working, it's a very high pitched sound.

It's a great technology though - Ive taken handheld shots at 1/6 and managed it, in fact I've even taken a few at 1 or more seconds and they've came through ok. Then again, I reckon I have a steady hand as I can get acceptable photos on my non IS Sigma 10-20 at 1s...
 
This is a control problem I believe.

The motion sensors that feed information to software that decides how to counter-act shake also feed noise (as electronics do).
In a sturdy tripod, at rest in an environment without wind or vibrations (road nearby), the image should show no movement.
However the noise is still being fed to the system. The system which is not working out this fact (I think different system have the same issue), reads this as real vibration and tries to compensate. This introduces artificial vibration which needs to be counter-acted again...
A system can actually spin out of control completely if the right control protocol and parameters are not used.

There is another issue, which happen with Pentax (dunno if its the same with other systems). SR (shake reduction) is only put to action when the shutter is half pressed, and the shutter should only be released when a warning symbol pops up into the viewfinder. Presumably the software is reading the shake profile and determining how to act against it. Not sure how it is working, but if you press the shutter before this you either put wrong parameters into action, or no action at all.
 
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