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Old Jul 15, 2006, 12:43 AM   #1
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How does Canon's IS work (how to operate it)?

Say you are shooting a building at 400mm with IS off and you have a correct exposure using f/5.6 @ 1/400sec.

You turn IS on; it doesn't have any effect on shutter speed, does it? It simply allows you, when you shoot at f/5.6 @ 1/400sec (say the IS provides 2 full stops), to shoot at the same aperture and shutter speed...only the picture result is as if you shot it at 2 full stops faster than 1/400sec.

Is this theory correct?

I'm having a hard time wrapping my head around this (what's new!).
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Old Jul 15, 2006, 11:37 AM   #2
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IS simply helps tocancel out minor shake caused by the hands moving when taking the shot. Not sure if the entire sensor moves or just the bit of the focus where the light is directed onto the sensor , still it works nicely for roughly 2 stops, maybe even 3 ..

The old rule (*) was the minimum speed to shoot at to have no hand shake burring the pic was 1/focal length

Eg shooting at 400mm ? then you need 1/400s or faster.

Modern cameras with ISgive 2 stops (maybe 3)

So, at 400mm , 2 stops would enable you to shoot at 1/100s

If you already have the correct or faster shutter speed for the conditions then fine, IS will not need to do a lot, but you might as well leave if on, its not going to hurt.

Some people and some manuals say turn the IS off when on a tripod, never noticed a difference off or on in this case , so I just leave IS on all the time and forget about it.



(*) The old rule was of course developed by people who have the camera in classic photographer pose, ie arms into the chest, camera hugged to the face , as they looked through the viewfinder.

If you are using the modern way of shooting, arms length looking at the lcd, one handed, while the other handwaves at friends, then all bets about minimum shutter speed to reduce shake are off ! :G

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Old Jul 16, 2006, 2:10 PM   #3
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If you are talking about Image Stabilization in their SLR lens line (which you can use on a DSLR as well) then I can help you out there a little bit.

The lens has an element which can be moved by micro motors to bend the light back and remove the shake. It compensates for the shake by changing the light path, nothing more. The lens also has gyros built in that to detect the shake and then drive the motors to compensate for it.

The lens element is "locked" into place (it can't move) when IS is turned off or when the shutter is not pressed.

It has absolutely no effect on shutter speed. Some people say it effects the starting of AF, some day it doesn't. I don't know which is true.

The claims about it making your camera work like it has a faster lens is really just marketing speak to an extent. If you could take the image at f5.6 1/400 (your example) with a 400mm lens then the average person won't have any camera shake issues. What IS is claiming is that you could also take the picture at f4 1/200 @ 400mm and you also wouldn't have any shake issues. It doesn't make the lens faster, adjust the shutter speed or anything like that. It just dampens/removes the effect of motion blur that would otherwise occure when shooting at 400mm @ 1/200th.

Does that help?

I know that I live by IS on my big lens. I have so much magnification that even a strong wind would mess up my picture. I regularly take good pictures at 840mm at 1/400th of a second.

Eric
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Old Jul 16, 2006, 2:21 PM   #4
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Thanks for that eric, that explanation did help.
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Old Jul 18, 2006, 1:09 PM   #5
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Glad to help. I read an article about Canon's IS awhile back, but didn't save a link.

I can't wait until Canon is forced into putting IS into the camera its self (assuming it works just as well as what they have now.) But it isn't in their interest to do it, only ours. Maybe some day...

Eric
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