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

Started Apr 6, 2013 | Discussions thread
Detail Man
Detail Man Forum Pro • Posts: 16,816
Sony RX100 compared to Panasonic LX7 - Pros and Cons

Mikedigi wrote:

Dunno, I don't have either, but these specs are intriguing:

LX7:       298g, 110x68x46mm, 1/1.7" (7.44x5.58mm) sensor, 10mp, 24-90mm efl.

RX100:   240g, 102x59x36mm, 1" (13.2x8.8mm) sensor, 20mp, 28-100mm efl.

One might say that the Sony's sensor area/weight ratio is impressive.

Compared the two cameras using DxOMark data at:


The rated pixel-pitches are 2.4 Microns for the RX100, and 1.96 Microns for the LX7. The native 3:2 aspect-ratio is 5472x3648 (19.961856 Mpixels) for the RX100, and 3776x2520 (9.515520 Mpixels) when selected for the LX7.

The ratio of the active area of the RX100 image-sensor (114.980 mm^2) divided by the active area of the LX7 image-sensor (36.555 mm^2) equals 3.1454.

DxOMark DR, SNR data takes Quantum Efficiency, Photon Shot Noise, Read Noise into account. It does not take any non-random, periodic Pattern Noise (banding phenomena) into account.

The same Saturation ISO (81 for LX7 at rated ISO=100, 81 for RX100 at rated ISO=80) means that the image-sensors received the same Exposure at maximum linear illumination levels.

("Screen" data) Dynamic Range and Signal/Noise Ratio was used, and normalized to the same display size using the square-root of the ratio of the different 3:2 aspect-ratio pixel-dimensions.

Under the above conditions, RX100 Dynamic Range measures 1.014 EV (stops) higher than the LX7, and the RX100 Signal/Noise (18%) measuress 0.601 EV (stops) higher than the LX7.

These conditions of comparison correspond to an equal-framing condition where the Depth of Field (DOF) of the RX100 is 1.77 times shallower than the LX7 - and the RX100 performs better.


Under equal-framing conditions with the same perspective (Camera to Subject Distance), the same Focal Length divided by F-Number ratio (the same virtual Aperture diameter), with the LX7 and RX100 lens-systems both at adjusted to 90mm FL - the Depth of Field (DOF) will be the same.

When the Shutter Speed used in both systems is the same, the Total Light will be the same. The Total Light illuminating each of the image-sensors is the product of the individual Exposures (amount of light per unit area) multiplied by the individual image-sensor active-areas. The amount of Total Light Transduced depends on the specific Quantum Efficiencies of the individual image-sensors.


In the equal Depth of Field (DOF) condition described above (where the same amount of Total Light illuminates both image-sensors), the required Scene Luminance will differ (because of the difference in the lens-system minimum F-Numbers, as well as any existing differences in transmission loss which cause the T-Numbers to be slightly different for the same F-Number).

At 28mm Focal Length (assuming that the minimum F-Number of the LX7 remains at F=1.4 at 28mm FL, which may not be the case, don't know), the RZ100 requires (as much as) 0.725 EV (stops) more Scene Luminance at the same Shutter Speed than the LX7 for the same Exposure.

At 90mm Focal Length (assuming the RX100 minimum F-Number has reached F=4.9 at 90mm, anyway, don't know), the RX100 requires 2.182 EV (stops) more Scene Luminance at the same Shutter Speed than the LX7 for the same Exposure.

However, the ISO Sensitivity of the the RX100 can be adjusted up to a Saturation ISO of around 164 (equal to slightly higher than the manufacturer-rated ISO=200) without having a lower Dynamic Range than the LX7 at manufacturer-rated ISO=100 (Saturation ISO=81), and the ISO Sensitivity of the the RX100 can be adjusted up to a Saturation ISO of around 186 (approximately equal to a manufacturer-rated ISO of around 230) without having a lower Signal/Noise Ratio (18%) than the LX7 at manufacturer-rated ISO=100 (Saturation ISO=81).


Summary: In relation to RAW-level performance (without regard for any differences between the in-camera JPG engines), at the same Scene Luminance and Shutter Speed, the RX100 operated at manufacturer-rated ISO=200 will have slightly higher Dynamic Range and Signal/Noise Ratio (18%) than the LX7 has when operated at manufacturer-rated ISO=100, ...

... for a Scene Luminance that is that is (at least) 0.275 EV lower than that needed by the LX7 at 28mm Focal Length, and (as much as) 1.182 EV higher at 90mm (35mm equivalent) Focal Length.

While the LX7 compares well with the RX100 in terms of Dynamic Range and Signal/Noise Ratio (18%) under the equal DOF conditions (which is an expected and commonplace result), the 45% higher pixel-resolution of the RX100's more than twice as many pixels is a tangible and significant advantage. The RX100's higher Color Sensitivity is also significant (see the relevant DxOMark data).

Further, if the user is willing to trade some of the LX7's rather copious Depth of Field for higher Dynamic Range and Signal/Noise Ratio, the RX100 can quite significantly outperform the LX7.

DM ...

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