So I am sitting here during some rare free time, and I am reading a discussion on why Canon should put IS in body and I am kind of laughing to myself and decided to share some of my thoughts about IS here. For those who do not know, IS stands for Image Stabilization.
First of all, in my opinion, IS has limited uses. It is absolutely necessary, in my opinion, in long lenses starting at about 400mm. Even on a tripod or monopod, the lenses are so large and heavy that some camera movement is bound to occur, even at higher shutter speeds. Having IS in these lenses helps cut that down greatly. But having IS in other lenses does only two things.
1. Drain your battery quicker.
2. Empty your wallet quicker.
Now, I do very little landscape photography and focus mainly on action and news, but I honestly believe in the 1/focal length rule for the most part. What ever lens you have on, as long as you can keep the shutter speed at least at or above the focal length, a 200mm lens would be 1/200th shutterspeed, you are going to have a sharp photo. Using slower shutter speeds than this can introduce camera shake....if you are not careful. Holding your breath, using a wall, table, or chair to steady yourself, or using a bean bag, monopod, or tripod is going to be cheaper and do a better job. Most landscape shooters will use a heavy duty tripod, cable release, and set their camera up for mirror lockup. People seem to think that in camera IS will solve that problem, but it wont.
In order for the in camera IS to work, the sensor has to move around to adjust for camera movement. While this movement is only a millimeter or two, you are now making your sensor even smaller. What if you are trying to fill the frame with something specific and the sensor shifts that 2mm, and suddenly along the edge of your image there is something that you do not want, or, worse yet, looking through the viewfinder, you can not see that the IS is going to do this because it is no longer OPTICAL. With in lens IS, you can see the IS smoothing the bumps out. In camera, you will see nothing.
Also, in lens IS is more accurate. IS from a 600mm lens is different than IS from a 400mm lens. The 400mm is tuned to give the best possible results from the 400mm focal length. You put the 400mm IS into a 600mm lens and compare it to a 600mm lens with the 600mm IS mechanism in it, the one with the 400mm IS will be less accurate. Basically, in lens IS is fine tuned for the lens it is in. In camera, you are either going to have IS that falls short compared to lens based IS or you are going to see camera's that either loose some features to make room for the IS software and mechanics. There is only so much room inside the cameras for all the data they need to work, and only so much room for the processors that make this data work. So, you have a Canon 30D. Pretty good AF, quick, accurate. Buffer clears out ok, not super fast, but better than previous models. Suddenly Canon releases a 35D, basically a 30D with in camera IS. You think great! A camera that is killer already, now is even better. You go out and switch that IS on and the first thing you notice is that the autofocus is moving a bit slower, not too noticable, but it is a tad slower, and not locking onto subjects as quickly. Take a burst of 4 or 5 RAW photos and suddenly you notice the buffer is taking for ever to empty as the images are written onto the memory card. Now, I am not saying that this would happen, but in all honesty, the 30D has one main CPU to handle all the cameras processing. 1D series has two, one for AF, one for everything else. Adding in body IS is going to slow down the camera slightly.
Another item that people tend to over look is flash sync. I do not know why this is, but it appears that in camera IS reduces the flash sync. Most Canon cameras are either 1/200th or 1/250th of a second flash sync, with the original 1D at 1/500th of a second. Adding in camera IS will change this. I do not have the specs in front of me, but I remember the Minolta 5D had a 1/160th of a second X-Sync without IS, turn IS on, and that dropped to 1/125th of a second. Shooting in studio and using studio strobes to shoot high school sports, 1/500th on my 1D and 1/250th on my backup XT (I know it says 1/200th, but I have successfully strobed at 1/250th) is a major necessity for me. If in camera IS is going to slow down the X-Sync, then there is absolutely no way in the world I will get a in camera IS body.
I do see how IS can be useful for some sports shooters. Shooting a baseball game under sunlight and having to drop your shutter speed down to about 1/60th to quickly take a shot of someone in the dugout, IS would be a benefit, but for the most part, with the exception of long lenses, my opinion is that IS is a gimmick.
Some of the greatest photographs of all time were taken long before IS, Autofocus, even color film, and to get them, even if it meant having an assistant help you, a good, sturdy tripod was use, and in my opinion, there is no better reduction of camera shake out there than a good, heavy tripod with a very sturdy head.