Since its announcement exactly 4 years ago the GH5S has been an enigmatic and successful camera for Panasonic. Today 4 January 2022 it still retails at £1,899 and it has upheld price more than the original GH5.
You would wonder who would want to get a 10 megapixel camera without stabilisation and the answer is many people that are solely focussed on video. The camera has built a reputation for low light performance and dynamic range and has been praised for its ‘color science if there is such a thing.
So after using the GH5M2 for six months I decided to rent a unit from Wex Photo and run a side by side comparison for myself.
When I say side by side I do not mean just in theory I mean in practical with the cameras close to each other and shooting the same scene.
For my tests I used a light box and a set of grey, white and color checkers and the same identical lens Panasonic 30mm macro. And for the outdoor scenes I set the GH5s with a Panasonic Leica 15mm 1.7 and the GH5M2 with a 10-25mm. As the GH5S has a multi-aspect sensor I needed to zoom the lens to less than 14mm to get the same field of view.
Before getting into the actual tests it is time to debunk a few myths about the GH5s.
Less Pixels = Less Rolling Shutter not more Dynamic Range
Camera readout is limited mostly by the speed of the Analog to Digital conversion. So having less pixels helps readout and reduces rolling shutter. This is the reason why all camcorder and dedicated cinema cameras have the minimum amount of pixels required and nothing extra.
This is true for the GH5S, the reputable website CineD as well as dpreview show a benefit of a couple of milliseconds for the GH5S over other cameras with a 20 megapixels micro four third sensor. This may be important when doing panning shots or using the camera on a dashboard or gimbal.
On the bigger pixels helping dynamic range there are a number of sources that explain why this is not the case but more importantly the the GH5S sensor has actually a quad bayer structure with cells of 4.6 microns made of 4 pixels each. So in reality the GH5S sensor has 43.64 megapixels arranged in 10.91 million cells that give 10.91 megapixels in 4:3 aspect ratio 9.07 megapixels in the 17:9 wide format. So not only bigger pixels are no help to dynamic range but the GH5S sensor actually has more pixels.
The sensor in the GH5S does not have higher dynamic range than other MFT cameras
Photonstophotos managed by Bill Claff is the only site that has measures of almost all camera models. While engineering dynamic range is purely determined by the difference between saturation signal and lowest readable signal, photographic dynamic range is what we see and is generally determined from setting a defined SNR for the image scaled to 12″ size long or 8 megapixels. This is roughly the 4K video resolution so it is a good starting point.
From this graph we can see that the G9, although based on the same sensor of the original GH5, outperforms the latter and the GH5s when it comes to dynamic range.
I am always cautious with measures taken by others so I did a full test and asked Bill to check the difference.
While in some cases there was an improvement of 0.18 Ev this would not be sufficient to push this sensor above the G9.
So the Panasonic GH5S sensor does NOT have more dynamic range of other Panasonic cameras with more pixels on the same format although it does quite well and at high ISO outperforms the GH5 at RAW level.
The multi aspect sensor has a bigger size in video but this does not improve dynamic range significantly
Due to the multi aspect ratio it is true that the sensor does not loose from a crop when changing aspect however we need to understand more what the potential benefit is.
A higher megapixel sensor with pixel of 3.3 microns will use its whole width and a cropped part of the height. If we look at 5184×2916 pixels surface this measures (5184×3.3)x(2916×3.3)=164.62 square millimeters. The GH5S with a cell size of 4.6 microns will have a surface of (3840×4.6)x(2160×4.6)=175.5 square millimeters.
Considering that dynamic range is proportional to the square root of the surface the improvement would be SQRT(175.5/164.62)=1.032 which in Stops is 0.046. So the larger area does not really do anything in 16:9 aspect ration.
In 17:9 the situation is a bit different and this benefit is 0.14 Ev still nothing so large to have a very significant impact.
During my tests I found the change of horizontal field of view which is what really matters confusing so personally I like to have a standard sensor with crop considering the benefits of multi-aspect are really limited.
The sensor of the GH5S has higher sensitivity
One of the features that the GH5S has is the so called Dual Native ISO. This is a marketing term for the Aptina DR-PIX technology which has been implemented by Sony for some time.
A white paper is here as you can read the technology enables sensors to increase sensitivity at the expense of dynamic range. The potential improvement is up to 5 dB however this is only true for very low light levels. To give an idea at deep twilight there is around 1 lux so with an exposure time of 1/50 of a second we have 0.02 lux*s this is not in the core range for this technology so more is required.
Back illuminated sensor give the additional sensitivity required as explained on Sony semiconductors page.
Now the combination of dual gain and back illumination means that the GH5S can do better at low light levels but also can tolerate very high levels of ISO. So the GH5S has additional high ISO capability for around two stops which means you can almost shoot in the dark. The key question is when does this matter when you have a fast lens.
Looking at an exposure waterfall calculator we can see that with an f/1.4 lens at 1/60 and ISO 3200 we can still cover twilight which is when public illumination is switched on.
In general terms all being equal the GH5S would have around 2/3 stops benefits in low light or in deep shadows compared to other cameras with MFT sensor.
This is quite interesting to test and quite simple using a color checker and a noise reduction software like neat video.
Here the first two samples are grey and black patches in VLOG at ISO 1600 using the Low Gain setting.
We can see that while the noise level on the middle grey is contained the black patch jumps to 4.4.
If we take the same reading manually selecting the High Gain range we can see how the situation changes.
On the middle grey we are in a very similar situation. However when we look now at the black patch we can see that the level of noise has dropped significantly.
So we can see that switching the camera from low to high gain at the same ISO has a significant benefit on darks in terms of noise.
VLOG to the rescue
With what we have said so far there has not been enough to substantiate why the GH5S would have more video dynamic range than the GH5 but VLOG comes to the rescue.
When Panasonic introduced the Varicam 35 in 2014 they were presented with the issue of having too much dynamic range.
Panasonic already have their CineLike Gamma that was able to manage 12 stops of dynamic range however this was no longer sufficient.
So the Varicam35 was provided with RAW output and with AVC Intra recording on their expensive expressp2 cards. VLOG provided an opportunity to compress the camera dynamic range in a 10 bit container that could then be recorded on card.
Panasonic made a first attempt to deliver VLOG to their Lumix with the GH4 however at 8 bit depth it did not work well. The GH5 is the first camera to have a 10 bit implementation however due to the smaller sensor it was limited to a smaller range called VLOG L which covers 12 stops of dynamic range.
A report by EBU indicates that the GH5S has more dynamic range in both CinelikeD and HLG modes compared to VLOG. Those are not scientific but are a suggestion that perhaps for a sensor with a maximum dynamic range around 12 stops VLOG is not the most efficient option. HLG presents challenges due to the color space and gamut differences however CineLike D does not require anything specific to process. Users have complained about the color accuracy of CinelikeD and generally Panasonic has been sponsoring VLOG and so have many websites under the assumption that this was the best way to preserve the full dynamic range.
While this may be true for larger sensors it would appear that this is not definitely true for the smaller MFT format.
In addition the implementation of VLOG among different camera is not the same as I already wrote here.
So in summary it is true that if you want to use VLOG the GH5S is a better option with a benefit that can be around 1 stop at high ISO over the best performing MFT camera at time of writing the GH5M2.
If you want to see the behaviour of the GH5S using a color checker you can appreciate the low level of noise at high ISO.
Color Accuracy and White Balance
I used a vectorscope to evaluate how the GH5S reproduces hues in VLOG. All tests done with factory settings and official Panasonic VLOG
You can see that the skin tone marker is exactly on target however red is more saturated than other colors and cyan is desaturated
The blue use is also shifted towards cyan.
This means that the GH5S can potentially produce a red cast and not give deep blue skies.
The weather was rubbish during my tests however from this example you can see how the red is definitely overboard by looking at the hat of the runner that comes on the scene.
This is something to watch out and a hue correction in post is required in most cases to bring things to normal.
Note that this issue with VLOG and the oversaturated red is also present in the GH5M2 that has very much the same color science or lack of thereof and will produce reddish tones on your skin that need to be corrected.
Take into account that hue correction is not resolved by setting a custom white balance.
For the hardcore pixel peepers I have shot a whole sequence of xrite color checker at all ISO steps
On a positive note the GH5S in VLOG meters correctly unlike the other GH5 siblings that are 1 stop overexposed.
You can see on the waveform monitor that setting the target at zero gives middle grey exactly on 50% on multi metering. On spot it will go at 45% which is what is expected.
Part 1 Wrap Up
From a series of quite simple tests done in a light box my expectation is that the GH5S will do ok but not sensationally in bright scenes and will do better in low light low dynamic range scenes.
In the next article I will analyse two side by side shots of the GH5S and GH5M2 in daylight.