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Old Apr 17, 2006, 6:33 PM   #1
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i heard that the 5d can shoot at a lower iso (or faster shutter speed, or smaller aperture) than the 30d in the same lighting conditions because the 5d has a full-frame sensor. how true is this?
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Old Apr 17, 2006, 7:12 PM   #2
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Absolutely not true.

The same settings will produce the same exposure on both cameras.
The digital noise in the image might be better on the 5D than the 30D. If so, that means you could increase the ISO as get the similar amounts of noise. If that is true, then you could increase the shutter speed and increase the ISO and get the same exposure (but less motion blur because you're using a higher shutter speed.)

But I don't know how good the 5D is on noise. If its better than the 5D, I don't know if it's "enough better" that you could increase the ISO by 1 stop and match the 30D's noise.

Did that make sense? I could explain it in more detail if you want.

Eric
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Old Apr 17, 2006, 8:16 PM   #3
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ISO is a standard measurement, so at the same ISO and in the same lighting conditions, both cameras should be using the same shutter speed/aperture (or a combination thereof) or something would be wrong with one of them. In other words, what you heard is not true.
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Old Apr 17, 2006, 8:16 PM   #4
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Oops, posted twice...
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Old Apr 17, 2006, 8:49 PM   #5
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ok i get what ure saying eric and michi. makes sense to me. let me provide a link to the original post at another website. maybe i didnt understand what they were saying over there.

http://dyxum.com/dforum/forum_posts....&KW=photov

the first reply by kiklop says:

I have decided to stay with KM and buy 7D primary for the best ergonomic. So, AS was never a reason but rather a bonus (despite the fact that I had A2).
But, after almost a year with 7D, I can only say that I hardly can't imagine owing a camera without AS.
FF or AS?
Tough one. I'm hopping for FF not only because wide angle, but also because FF will bring back (hopefully) the big large viewfinder dynax 7 have. But if I must choose, then I guess AS would be my choice.
But if FF means two stops of advantage because ISO 1600 will be equally good as ISO 400 on cropped camera, then I would choose FF without any doubt

so...maybe this means something else?
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Old Apr 18, 2006, 9:11 AM   #6
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They mean what I said.

It's a secondary effect of the larger sensor. It isn't "Because it's a larger sensor you can use a higher shutter speed" They are really saying "Because the larger sensor has less noise I can increase the ISO and get the same image quality - this will let me use a higher shutter speed."

The thing on the sensor that samples the light is called a photosite. The general rule is that the closer you pack them together the higher the noise is. Another general rule is that the smaller the photosite the more noise you get. More noise means reduced image quality (masks detail... and just looks bad.)

If you keep the same number of photosites and spread them out over a larger sensor (in this case a full-frame sensor) then you should reduce the amount of noise. If you can reduce it enough, you can use a higher ISO setting and get the same image quality. Getting that much less noise might not happen, but there should be less.

So if you take the picture at ISO100 1/200 f5.6 with a smaller-sensor camera and you find that ISO200 on a different camera looks just as good noise wise, then you could take the same image at: ISO200 1/400 f5.6. Doubling the shutter speed could be the difference between capturing or throwing out the image.

Now the above statement is true even if the sensor isn't larger. Companies get better at reducing the effects of noise all the time. The noise on the Canon 20D was better than the noise on the Canon 10D. And the 20D had more photosites on the same size sensor! This statement holds true no matter what the sensor sizes are:
ISO100 1/200 f/5.6
ISO200 1/400 f/5.6 or ISO200 1/200 f/8
If both of those produce an acceptable quality image, then shoot at ISO200 and either get a higher shutter speed or use a larger aperture. It gives you flexability to get the shot that you want.

On my camera, ISO200 is good enough for me. I almost never use ISO100, even though I have it. This is because the noise isn't that bad at ISO200, and I need the shutter speed to stop the animals in motion.

Eric

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