BeachTog757 wrote:
This may seem like kind of a newb question but I am in what is for me uncharted territory.  I have a Canon EOS 5D Mk3 and several lenses.  My long lens until recently has been a Sigma 70-200mm F2.8 HSM which I absolutely love.  Yes I know it is old but it does the job and has become like an old friend, hard to walk away from.

I just bought a new lens, the Canon 70-200mm F4 USM IS.  I haven't used it at a photo shoot yet but so far the photos I have taken in my back yard have been pleasant.  I have a question about the IS.  I know what "IS" is and how it works but I am a little in the dark as to when to use it.  A few photographers I have talked to tell me to leave it on all of the time which I don't know if I agree with.  I am used to increasing the ISO when I need higher shutter speeds and /or f-stops.  I do a lot of sports, Soccer, Baseball, and Motorcycle Racing to name a few.  At 7:00AM I normally have my ISO set at 800 or 1000 to give me shutter speeds of 1/500 sec or 1/1,000 sec at f4.0.

I am guessing that the prevailing wisdom is saying to use the IS on my lens but I have to ask why if I can get what I need the conventional way.  Thoughts are appreciated.  Thank you.

I have EOS 5Ds, Mark II, III and just got a IV. All my glass has the little red ring around them. Each of those lenses arrived with IS turned on and I have never turned the feature off. Whether it's a model in front of me, a landscape or the occasional trip to Laguna Seca, I leave IS on.

I have never had a focusing problem. Occasionally, in low-light situations, the camera thrashes itself trying to focus but nothing too annoying. One thing I do in my set-up is I have just the center focusing point active, I turn off all the others. Just my preference.

Rick

SayCheeZ!  wrote:
The rule of thumb is to use on the IS when hand holding the camera for a shot that's fairly still
or in low light or scenes that require slow shutter speeds.

Turn it off when it's mounted on a sturdy tripod or when shooting the sports or races that you've mentioned (especially when panning).

This is the correct answer. Basically what's happening with IS is that it keeps elements inside the lens in a state of floating, per se, so that when you are holding the lens it's compensating for you making subtle motions with your hands. Thus, it is compensating for your motions and helps to keep the image more stable. This allows less motion blur in your photos and also helps with lower lighting conditions as well. There should be different selectors as to what type of IS setting you want to use on the lens, usually it's something like fast action, panning only, etc. I'm not familiar with Canon's methodology on those but that's generally the gist of it. If anything, read what the manual tells you. It's pretty straight forward.

However, any time you have the camera on something very stable, like a tripod or monopod or are bracing it against a wall or something like that, you need to turn the IS off. Basically it will cause instability in your shot and will be literally working against you as the lens is trying to compensate for a problem that no longer exists in this case. So anyone who's telling you to leave it on all the time is giving you bad advice. It will even tell you this specifically in the manual, I'm sure.