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Old Dec 6, 2009, 11:27 AM   #31
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The root issue is that if you want the maximum resolution with any given equipment, you will have to take the maximum practical care. To take full advantage of higher resolution equipment, more care is needed.
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Old Dec 6, 2010, 3:22 PM   #32
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Ok I understand that the 1/FL might not be enough without image stabilization,
so then my question is what does IS add.
I think that IS (in lens, or body) also has different results in function of the focal length.
What would make defining a new rule rather difficult.
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Old Dec 6, 2010, 4:50 PM   #33
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Ok I understand that the 1/FL might not be enough without image stabilization,
Not quite accurate. For the most part, the rule of thumb (Exposure Time = 1 / (Focal Length * Crop Factor)) is perfectly adequate. In some extraordinary circumstances (such as higher resolution image sensors or especially shaky hands) it won't be enough.

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so then my question is what does IS add.
In general, IS can quadruple the exposure time that you could use without it. That is, when using a 300mm lens on an APS-C dSLR, most people can get perfectly sharp images if they use shutter speeds faster than 1/450 second, without using IS. With IS, though, they can probably get similar results with shutter speeds as slow as 1/112.

But, if you've got a high resolution image sensor, or you're not very steady anyway, you may need to use an even faster shutter speed, such as 1/900 without IS or 1/225 with IS. So IS still gives you a 2 stop advantage, but that 2 stops is on top of what you would need to do, whatever that may be.

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I think that IS (in lens, or body) also has different results in function of the focal length.
Absolutely.

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What would make defining a new rule rather difficult.
As with any rule of thumb, it's a starting point. If it works for you, then fine. But if it doesn't, then you need to make your own allowances for it. The benefit you'll get from IS will still be the same 2 stops that everybody else gets; the difference will be how well the rule of thumb predicted the results you got.
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