LX7 - does its IQ compete with e.g. Sony RX100?

Started Apr 6, 2013 | Discussions thread
Sean Nelson
Sean Nelson Forum Pro • Posts: 12,944
Re: LX7 - does its IQ compete with e.g. Sony RX100?

ultimitsu wrote:

"Faster" refers to the ability to use faster shutter speed while maintaining the same IQ.

I know what you mean by "faster shutter speed to maintain the same IQ", but I doubt many other people think that way.   For example, does "same IQ" mean a shutter speed fast enough to eliminate motion blur?   No, that's not what you mean.   You mean a shutter speed that lets enough light hit the sensor to end up with the same amount of noise.   That's really not the way most people think about shutter speed.

For the record, a lens of f/2.8 aperture and the same field of view shooting the same scene at the same ISO setting can be used with the same shutter speed on cameras with varying sized sensors.  That's because lenses set to the same f/ratio illuminate the sensor with the same brightness per unit of area (number of photons per square millimeter, for example).

What ultimitsu is saying is that the smaller sensors won't collect the same total amount of light, and therefore their images will be noiser.   By "total amount of light" he doesn't mean the brightness of the image (that's solely governed by f/stop), he means the brightness times the sensor area.   A larger sensor requires more total light to illuminate because there's more area to cover - just like a 60" TV requires more total light to illuminate than a 30" TV, even if the brightness per square inch is the same.   You need more bulbs back there to illuminate the extra area of the larger picture.

We all try to use the lowest ISO possible to reduce noise, and by doing so we're forcing ourselves to use a wider aperture and/or slower shutter speed.   Conversely, a larger-sensor camera can (in theory) use a higher ISO and still keep noise under control - this means that it can use a faster shutter speed (or smaller aperture).   That's what he means by larger cameras being able to "use a faster shutter speed while maintaining the same IQ".

But once most people choose a camera, they stop worrying about comparisons with other cameras.   They decide how much noise they're willing to live with, choose a maximum ISO accordingly, and from that point on they only worry about f/ratio and shutter speed.

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