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jcolwell wrote:
Handheld panning with IS in Mode 1 is a definite detriment, too. It's not because of "vibration", it's because of how the IS system attempts to compensate for hand shake (or wind, or etc.). The IS system is designed to compensate for small, harmonic motions (i.e. back and forth). For example, the IS system compensates for lens movement a bit "to the left", by rotating the IS optical group a bit "to the right". When the motion to the left begins, the IS begins a small rotation to the right. This works well when the motions go a bit left, then a bit right (or a bit up, then a bit down), but this strategy fails if the motion to the left just keeps going (i.e. as when panning to the left). In this case, the IS optical group moves as far as it can to the right (which isn't all that far), and then it "hits the stops", and re-centres the optical group. This causes a glitch in the matrix (i.e. a visible shift in the finder), and does not provide good results if you press the shutter while it's happening.
IS Mode 1 attempts to stabilize in both horizontal and vertical directions, and IS Mode 2 senses in which direction you are panning, and stabilizes the other direction. IS Mode 2 only stabilizes in vertical or horizontal panning directions, and can 'fight' your motion if you're panning in a diagonal direction (i.e. it will stabilize one of the direction components, and not the other); resulting in glitches in the stabilized direction, when the motion just keeps going (same situation as panning in Mode 1). IS Mode 3 avoids these issues by not stabilizing until the shutter button is pushed, and so it avoids trying to compensate for motions experienced before the shutter button is pushed.
IS will provide sharper images at shutter speeds faster than the "rule of thumb" (shutter speeds slower than 1/focal length, for FF camera), just as mirror lockup or EFCS (electronic first-curtain shutter) will provide sharper images at higher and lower shutter speeds than the "rule of thumb" region of shutter speeds from say 1/2 sec to 1/30 sec. In both cases, the camera or lens compensation system can provide better results in many situations outside their "design domain", but they can also can make things worse in some situations. For "very active" panning, like close-by BIF and track-side motorcycle racing, I turn off IS, because the rapid-rotation movement that I make when panning actually helps to stabilize the camera, especially with a big lens, and I don't need IS. If I transfer the lens to a monopod to shoot a stationary subject, then I turn IS on in Mode 1, if I have time and if I actually remember to do it....Show more →
Agree especially about the warning regarding IS use with 'very active' panning. I like taking DIF (dragonfly-in-flight) shots, a bit similar to BIF but even higher (angular) subject speed, so even bigger camera/lens movements required. With my old 4/300IS this was impossible with IS engaged, try it and the lens produces really scary sounds from the IS system. Haven't tried yet with the 100-400II, maybe mode3 would work for this but I doubt it. So in general, I switch off IS for moving subjects (which usually means shutter speeds above 1/800sec or so).
I did some indoors testing with my new 100-400II on 80D camera regarding IS, mostly at 400mm focal length for static subject at 5-10m distance, and it's 'complicated'. Around 1/125-250s the IS wasn't very effective (probably due to mirror/shutter shock), at 1/20-1/100s it works great compared to no IS (plus of course the VF stabilization is a plus). At faster shutter speeds like 1/500-1/1250 the IS increases chances of a really sharp shot compared to no IS, but it's not a huge difference and sometimes images with IS have visible 'shake' as well.
Testing outside with wind, standing on less stable surface and maybe with a more tired photographer the results might be different again ;-)
For my DIF shots 1/2000s or faster is required for really sharp shots (= no IS advantage except stabilizing VF), but often the lighting conditions do not allow that. Also, I find images with some wing blur usually more pleasing, which requires shutter speeds of 1/250-1/800 (= some IS advantage)
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