FPS and IS

Since I have obtained my 1D III, I have noticed something about FPS that I have not seen anywhere else. I've searched google and the forums here, and cannot find any information to back up my findings.

Basically, I have the camera set to AF-on focusing and drive priority - Even in manual focus will it slow down the FPS. Just out of curiosity, I disabled IS on my 300mm F/4 and magically, it shoots the full 10 frames.
I produced the same results with a 28-135mm IS.
The same occurs even after waiting 1-2 seconds after triggering the start of IS.

However, my 70-200mm F/2.8 IS seems to have no effect on frame rates with IS enabled or disabled (which I thought was strange).

Weird enough, I also noticed a slowdown with the 50D and 300mm F/4 IS combo as well.

Has anyone else noticed this? If not, could this be the problem why some people are still having trouble with the FPS on the 7D or 1D cameras?

What shutter speeds are you using? You need to be up there to wring the max FPS from the body.

Bradfordguy wrote in post #10185850
What shutter speeds are you using? You need to be up there to wring the max FPS from the body.

Thanks for the reply.
Yes, I understand. However I am not having a problem with my bodies and am getting my full 10 frames. I'm merely presenting something that I had found by accident that may be a problem for other Canon users.

All shutter speeds are of at least 1/1000". and 100 ISO.

Well if you're using "One shot" AF that will slow things down as the shutter will not fire until focus is achieved. Probably not the issue since you seem to think the IS is the root of the problem.

flowrider wrote in post #10188931
Well if you're using "One shot" AF that will slow things down as the shutter will not fire until focus is achieved. Probably not the issue since you seem to think the IS is the root of the problem.

That and he said he had it on manual focus.

Stick it in AI servo and give it a try, I've never used IS so I couldn't comment.

If you're looking for max FPS, as has been said, you need a pretty fast shutter. Why is IS even turned on? That makes no sense to me. Obviously, anything extra that the camera needs to do before releasing the shutter is going to take away from the max FPS. Add IS into the mix (especially why you don’t even need it) coupled with needing to update focus for the next shot and waiting for the prior shutter cycle to complete, and you’re going to lose some speed.

IS shouldn't affect the shooting speed. The camera doesn't know the lens is doing IS, in the Canon EOS system there is no feedback to the camera body to tell it that IS is going on, none at all. The only possibility I can think of is that it might prevent focus from being achieved while it is "spinning up" but once it is locked on I can only think it will help the focus by holding the image steady.

The only thing I can think of for the OP is that the IS is taking additional battery power. The Mark III's 10 fps speed is so fast that it already stresses the battery. Have you checked to see if the battery light flashes when it is slowing down? The Mark III has a display on the top LCD which indicates that low battery power is causing lower drive speed to be used. Turning IS off would lower the total power requirements which could cause what you're seeing, especially if your battery is old or depleted.

flowrider wrote in post #10188931
Well if you're using "One shot" AF that will slow things down as the shutter will not fire until focus is achieved. Probably not the issue since you seem to think the IS is the root of the problem.

My fault. I failed to mention that the primary mode of focusing was in AI Servo. I guess I assumed you all would pick up on that from the camera being in Drive Priority.

I was shooting a PGA event and normally keep IS off. Somehow the 300mm F/4 brushed up on my side as I was running and enabled it. The FPS was slowed greatly, I reviewed my settings and the only change I had made was disabling the IS; needless to say, the camera was giving of max fps once again.

This is exactly why I thought it was so weird. The IS has no relay to the camera. Although, I haven't noticed the battery flashing, but power consumption is the only thing I can think of how it could possibly affect the camera itself. And it makes sense.

Like I said prior, I can only mimic this phenomenon with the 300mm F/4 IS and the 28-135mm IS. My 70-200mm f/28 IS has no effect on the FPS; the camera displays max FPS whether the 70-200mm IS is enabled or disabled.
And the 300mm F/4 also shows a slowdown in FPS even on the 50D (gripped) with IS enabled.