How effective is IS?

How effective is IS? For example, assuming the subject is stationary, which lens would experience less camera shaking used by the same person:

70-200mm f/2.8 or 70-200mm f/4.0 IS ?

If f/4 IS is more stable than f/2.8 without IS, then, how far can go down in aperture with the IS version to be equivelent to f/2.8?

It's not as straightforward as that. Depending on the conditions you're in, the extra weight of the f/2.8 may be easier to hold steady, or if you've been out for a while and are getting tired the lighter f/4 may be less fatiguing. Under the same lighting conditions, the f/4 IS will generally do better, and, if Canon's to be believed, it will have 2-3 stops advantage over the f/2.8 non-IS (after allowing for the slower max. aperture).

You see the thing is, with either lens if you have a shutter speed greater than say about 1/400 you won't notice any improvement with IS.

Now lets say that you set both lens at f/5.6 and you need a 1/160 shutter speed for proper exposure. OK, no problem with the IS lens, however not so good with the non-IS. So you bump up your ISO or open up the aperature, now you can raise the shutter speed and get a good sharp image, but at the cost of shallower depth of field or more noise in the picture.

I would estimate that about 10-20% of my photos are better because of IS. That is not a huge amount because most of my shots are either outside with good light or inside with flash or strobe - in other words IS doesn't help. However, sometimes IS is the difference between good shot and no shot.

Depends very much on what you need and technique - if you need a 2.8 aperture to freeze motion no amount of IS is going to do that.

I recently had to send a 100-400L IS in to Canon for an alignment. They ended up replacing the whole IS unit inside, and cleaning and aligning the lens. Yes, it was better when it came back. But now, how long will it last before it needs it again? One bump, two? No bumps and good for a couple years? No telling.

But for me, I am going to stay away from IS in the future and just buy faster glass and live with it.

Just get the 70-200mm f/2.8 with IS and don't worry about it

IMHO, the 70-200 f4 IS is way overpriced. Considering you can get a new one, non-IS for around $520, is $700 more really worth it. I think if you are going for the IS, get the 2.8 IS, unless WEIGHT is the only deciding factor. f4 is too slow to use indoors or a wedding, with-IS or not. Unless you shoot everything outside, then it's a good buy, but then again, do you really need the IS?

I had the 70-200 f4 and 2.8 versions, and I loved the weight of the f4 version. The 2.8 version is really heavy, heavier than my personal tastes. I might be purchasing it for the next wedding season, but I really really dread that it's so heavy.

We've only 2 IS lens - 70-200 f 2.8/ 24-105 f 4. Easily hand hold the 70-200 to 1/50 sec - 24-105 to 1/15 sec. Shootng on 1D platforms (1.3) - suspect one could drop lower w/FF gear + and would need to 'go up' somewhat on a 1.6 platform - but that is just a guess!

Assuming that you're shooting stationary targets, I've tried the 100-400L IS and gotten clear images at around 1/50 sec at 400mm. Turn the IS off, and I had to shoot at 1/300 of a sec or so. In that respect, IS can be very helpful especially since it's only f/5.6 at 400mm.

blackshadow wrote in post #2207181
Depends very much on what you need and technique - if you need a 2.8 aperture to freeze motion no amount of IS is going to do that.

20 stop IS would

Also depends a lot on which IS unit. The newer ones are truly amazing. The 100-400 IS is certainly helpful but not as good as the 70200 2.8 or 24-105.

AdamJL wrote in post #2209580
20 stop IS would

Not really. Unless you mean freeze the motion of your arms drifting.

20stop IS would just allow you to shoot ridiculously slow shutter speeds, something like 20" haha...

24-105 hand-held for 0.4sec... IS is pretty effective, I'd say.

KevC wrote in post #2210483
Not really. Unless you mean freeze the motion of your arms drifting.

20stop IS would just allow you to shoot ridiculously slow shutter speeds, something like 20" haha...

That is correct and most do not get the correlation. IS allows you to hand hold at slower shutter speeds. In order to gain the stops, you have to have the stops in the first place. IS does not miraculously give you stops.

...not to mention is keeps your viewfinder from bouncing all over the place from camera shake...

IS also helps with panning shots in mode 2. It reduces the vertical motion so you get more panning keepers.