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

Started Apr 6, 2013 | Discussions thread
Re: LX7 - does its IQ compete with e.g. Sony RX100?

Cyril Catt wrote:

ultimitsu wrote:

But we are not comparing a fixed unit area, are we? we are comparing the entire image.

No. we ARE comparing the amount of light falling on a unit area, which results in a specific brightness of illumination, and therefore a specific exposure value.

That maybe what you are doing. that is not what I am comparing. There is no value in comparing the amount of light falling on a unit area. What gets compared ultimately is the image, which uses the whole sensor area. and that area is different on RX100 and LX7.

If you spread that light over a greater or lesser area the brightness, and hence the exposure vale, will be different.

But what do you mean by "exposure"? if the hole is the same sive, FOV is the same, SS is the same, the only thing is different is ISO, but the IQ will be the same.

As the brightness of the illumination on the sensor depends partly on the distance of the diaphragm from the sensor, it is meaningless to consider only the absolute area of the aperture and to ignore the focal length of the lens. An aperture with an area of 10 square centimetres at a distance of 100 metres from the sensor will provide far less illumination to the sensor than a smaller aperture of one square centimetre at a distance of 10 centimetres from the sensor.

That is correct. because the FOV is vastly different, meaningful comparison can only be done where FOV is the same or at the least similar.

NO. It is related to the inverse square law, which reduces the brightness of illumination in proportion to the inverse of the square of the distance between the diaphragm and the sensor.

This piece is incoherent.

As Wikipedia states it: “A lens with a larger maximum aperture (that is, a smaller minimum f-number) is called a "fast lens" because it delivers more light intensity (illuminance) to the focal plane, achieving the same exposure with a faster shutter speed.”

That is only true where FOV and sensor size are the same or similar.

NO AGAIN. The FOV and sensor size are irrelevant. The brightness of illumination of the sensor, and hence the required exposure, is related to the  f-number, which is calculated from the focal length of the lens and the effective diameter of the aperture. If the lens is a good quality one it will illuminate the centre and the edge of a large sensor with more or less similar brightness. So if you substitute the sensor with a smaller one, it will also be illuminated with a similar brightness.

But the FOV will be different thus it cannot be compared. if FOV is the same then lens is different.

May I suggest you look at an exposure meter and take note of the relationships between shutter speed, f-number, ISO, and illumination.

I suggest you do the same.

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