ISO / Sensitivity accuracy
The actual sensitivity of each indicated ISO is measured using the same shots as are used to measure ISO noise levels, we simply compare the exposure for each shot to the metered light level (using a calibrated Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV.
We found the GF1's indicated sensitivity when shooting JPEGs (standard settings) to be just under half a stop averaging ~0.4EV) lower than the actual sensitivity (in other words, the GF1 is around a third of a stop more sensitive than it says it is). By comparison the Olympus E-P1's indicated ISO settings are an almost perfect match for its measured sensitivity (these days most digital SLRs mave fairly accurate ISO values when used at their default settings).
|ISO 100||ISO 125||ISO 100|
|ISO 200||ISO 250||ISO 200|
|ISO 400||ISO 500||ISO 400|
|ISO 800||ISO 1000||ISO 800|
|ISO 1600||ISO 2000||ISO 1600|
|ISO 3200||ISO 4000||ISO 3200|
|ISO 6400||n/a||ISO 6400|
* Approximate values, default settings (except E-P1, which has Gradation 'off').
What all this means is that at the same ISO setting the GF1 will require a little less exposure than the E-P1 to get the same result. For example the GF1 might use a 1/15 second where the E-P1 needs 1/10th (all shutter speeds are 'rounded' so these won't be the exact values). In truth you could simply under expose the E-P1 by a third of a stop and brighten a little in post-processing.
Such is the rather imprecise nature of ISO measurements when shooting JPEGs that you could also switch the E-P1's auto gradation setting on to get exactly the same middle gray value for the same exposure - in other words you'd get essentially the same ISO values). It's certainly not worth worrying about.
ISO Sensitivity / Noise levelsISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. This works by turning up the "volume" (gain) on the sensor's signal amplifiers (remember the sensor is an analogue device). By amplifying the signal you also amplify the noise which becomes more visible at higher ISO's. Many modern cameras also employ noise reduction and / or sharpness reduction at higher sensitivities.
To measure noise levels we take a sequence of images of a GretagMacBeth ColorChecker chart (controlled artificial daylight lighting). The exposure is matched to the ISO (ie. ISO 200, 1/200 sec for consistency of exposure between cameras). The image sequence is run through our own proprietary noise measurement tool (version 1.5 in this review). Click here for more information. Room temperature is approximately 22°C (~72°F), simulated daylight lighting.
Panasonic DMC-GF1 vs Olympus E-P1 vs. Panasonic LX3 vs. Canon EOS 500D
- Panasonic DMC-GF1: Olympus 50 mm F2.0 Macro lens (via adapter), Aperture Priority, Manual WB,
Default Parameters, Noise Reduction Standard (0), JPEG Large / Fine
- Olympus E-P1: Olympus 50 mm F2.0 Macro lens (via adapter), Aperture Priority, Manual WB,
Default Parameters, Normal Picture Mode, Gradation Normal, Noise Filter Standard, JPEG Large / Fine
- Canon EOS 500D: Canon 50 mm F1.4 USM lens, Aperture Priority, Manual WB,
Default Parameters, Standard Picture Style, NR Standard, JPEG Large / Fine
- Panasonic DMC-LX3: Aperture Priority, Manual WB,
Default Parameters, Normal Picture Mode, Default Parameters, Noise Reduction Standard (0), JPEG Large / Fine
|Panasonic GF1||Olympus E-P1||Canon EOS 500D||Panasonic LX3|
Up to ISO 400 there's not a huge difference in noise levels (or the visible effect of noise reduction) between any of these cameras (even the small sensor compact, the Panasonic LX3, is pretty close). Once you get to ISO 800 and above the output starts to diverge, with the LX3 falling away rapidly (high ISO performance is still the Achilles' heel of compact cameras). Comparing the three large sensor cameras it's obvious they're all fighting noise pretty aggressively, and the main differences here are down to the type and strength of noise reduction being used. The EOS 500D does best balancing noise and detail (especially when you take into account its higher pixel count, which means a little less magnification is needed for the same reproduction size).
At higher ISO the difference between Panasonic and Olympus's approach to noise reduction is immediately obvious. Presuming that the amount of noise both have to deal with is roughly the same (it's essentially the same sensor), it's clear that Panasonic has chosen to concentrate (as usual) on chroma noise, leaving quite a lot of grainy luminance noise in the image (and therefore preserving more detail). By comparison Olympus has gone for heavier luminance noise reduction, producing a far smoother, but less detailed result.
Which you prefer is mostly down to taste as long as you remember two things: firstly, it's a lot easier to increase luminance noise reduction in post processing than it is to bring back detail never captured in-camera and secondly all these cameras offer noise reduction options that reduce the differences significantly.
|Panasonic GF1 vs Olympus E-P1 vs Panasonic LX3 vs Canon EOS 500D|
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.
Raw noise compared (ACR)
Switching to raw and converting using our benchmark developer (Adobe Camera Raw) - with all noise reduction turned off - reveals just how similar the GF1 is to the E-P1 and, for that matter, to the EOS 500D. We consistently measured the GF1 as slightly noisier than the E-P1 at anything over ISO 800, so to make sure we weren't seeing some Adobe Camera Raw issue, we tried again with several raw converters, including DCRaw. In every case the GF1 showed visibly more chroma noise, leading us to conclude that something in the signal pathway on the E-P1 is doing a better job at reducing - or not introducing - noise.
|Panasonic GF1 RAW||Olympus E-P1 RAW||Canon EOS 500D RAW||Panasonic LX3 RAW|
Four Thirds cameras compared (JPEG, default)
Before we move on let's take a quick look at how the G-F1 compares with the other two Micro Four Thirds cameras (the Panasonic GH1 and Olympus E-P1) - and the nearest Four Thirds camera, spec-wise (the Olympus E-620). Three of these cameras are presumed to share the same 12 megapixel LiveMOS sensor, with the GH1 sporting a slightly higher-spec multi aspect ratio version.
Unsurprisingly there's not a lot between them up to ISO 800. At higher settings it's all about the amount and type of in-camera noise reduction being applied (remembering these are all at the default setting), with the Panasonic GH1 probably the best of the bunch by a whisker. By default the E-P1 applies a little too much noise reduction for our liking, but this is easily changed in-camera.
|Panasonic GF1||Panasonic GH1||Olympus E-P1||Olympus E-620|