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dont get me wrong, f/2.4 is a great change from f/2.8, but i think it should be looked at as a whole. the combination of an f/2.4 with the sharper 8 megapixel camera, CMOS sensor, AND noise reduction....THAT is an upgrade. they all benefit from each other.

think of it this way...you can have a 70-200 f/2.8 on a cropped sensor. yeah it'll be cool and will work....but not nearly as amazing as a 70/200 f/2.8 with vibration reduction on a 5D Mark II or D700 full frame sensor.
 
There is quite a bit of confusion on this thread. Let me try to distill it for you:

the f/2.4 aperture is a half stop (of light) away from f/2.8 (http://en.wikipedia.org/wiki/F-number#Typical_one-half-stop_f-number_scale).

While this is good in that the camera will be able to take photos in slightly darker conditions..... it is also bad because the 4s now has 8 Megapixels instead of 5 MPixel with a camera sensor that is the same size.

The iPhone 4 camera is on par with low end, $80-$100 ultracompact point and shoot cameras (only with a worse flash and no zoom).

Aperture does not increase sharpness. Sensor resolution (MPixels) does not necessarily increase sharpness.

You will get a slightly better shutter speed out of the iPhone 4S because of the larger aperture. I expect that noise from poorly exposed areas will be noticeably worse due to the larger resolution.

I know that you guys love your iphone4 cameras.... but improving it is a lot like putting a wing on a Honda Civic. Window dressing that doesn't change the limitations inherent in the design of the hardware.
 
I've learned a lot from this thread.

Although it reads like a bigger number f stop would mean better depth of field for some scenarios for sharpness

Example http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

The first pic in the left looks better than the one of the right. As the iPhone has a smaller number appeture, you couldn't get the shot on the left. I have to remember though, it's only a phone...

what i meant but that is something like this pic:

Comparison of f/32 (top-left corner) and f/5 (bottom-right corner)

http://upload.wikimedia.org/wikipedia/commons/8/86/Jonquil_flowers_merged.jpg

you can see here that the f/32 is better than the f/5
 
Wow everyone has already replied with a whole wiki on f stops. :). As some pointed out already the iPhone 4s will have faster shutter speed but the sharpness could be a little lower depending on the subject and the distance. For example taking picture o a coliseum ( the round arena thing) from the front, focusing on the center, considering its a circular, the outer parts will be blurrier as the focus will be different with the bigger aperture on the sides. Saying that however it will all depend of the distance. So it's very circumstantial. Depending on composition you can get sharper or utter shots.
 
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