Tuesday, 25 April 2017

GH5 e-shutter is slower!

The Lumix GH3 introduced a new concept in 2012: Electronic shutter. Meaning that you no longer had to rely on a mechanical curtain shutter in front of the sensor to start and stop the exposure, this could now be done purely electronically by the sensor itself.

The benefits are obvious: Less wear on the shutter if you want to make a time-lapse, for example. And a perfectly silent camera.

However, there was also a big downside: The sensor was scanned vertically during electronic shutter usage, and this scan was slow, taking a total of 1/10s. If you moved the camera, or the subject moved in this time, you would get skewed lines and weird effects. And can you hold the camera steady for 1/10s? No, that is impossible.

So the usefulness was rather limited. Future implementations increased the e-shutter scan speed, however, at the expense of the bit depth. Using only 10 bits rather than 12 bits normally, that would increase the scanning speed, but reduce the dynamic range capabilities. This was done, e.g., in the Lumix GH4, angering some users. And the scan speed was still quite slow, way slower than cameras from the Nikon 1 series, for example, with a 1/80s scan speed.

With this backdrop, the big question is: What about the Lumix GH5? What is the electronic shutter scanning speed and bit depth? Does it finally make the electronic shutter useful? That is what I will answer here, by comparing with two similar cameras:


Back: Lumix GH5 (left) and Lumix GH4 (right), and Lumix G85 in the front. Despite these cameras appearing to be the same size, they are in fact significantly different, with the GH5 being largest, and the G85 being smallest.

Speed of E-shutter readout


The Lumix GH3 electronic shutter had a readout speed of 1/10s, which is very slow. This leads to significant rolling shutter artifacts, that you can read about here. How do the cameras above compare?

One way to test the speed of the electronic shutter is to take a photo at a fast shutter speed in artificial light. For about a century or so, people have been using incandescent light bulbs for electronic indoor lightning. Even when used on alternating current (AC), the light is stable. Since the filament is heated, it emits light also when the alternating current is at zero.

However, traditional incandescent light bulbs are now being replaced with the energy saving fluorescent light bulbs. They tend to flicker at 100Hz (in Europe) or at 120Hz (in the US). The lights don't flicker at 50Hz and 60Hz, as you might expect. This is since during each period, the electrical current reaches two peaks, see the illustration below:



Here are images taken at ISO 3200, 1/400s with the three cameras:

Lumix GH5Lumix GH4Lumix G85

Each yellow row represents 1/100s of scan time, and the more rows, the slower. So there is your answer, the Lumix GH5 has the slowest e-shutter scan speed of the three. Who would have guessed?

By counting the lines more thoroughly, I get these approximate scan speeds:

Lumix GH5Lumix GH4Lumix G85
1/22s1/30s1/25s

Bit depth


Having answered the first question, what about the second? Do you lose some bit depth, and, hence, dynamic range, when using the electronic shutter?

To find out, I took the same picture using the three cameras, and I underexposed by two stops. Then I increased the exposure by three stops in a RAW editing program. That reveals how much details are left in the shadows. I used ISO 200, the base ISO, in all the cases.

Here are the pictures, after adjusting the exposure by +3 in post processing, using the RAW file:

Lumix GH5Lumix GH4Lumix G85
Mechanical shutter
Electronic shutter

They look quite similar on first look, but some crops at 100% reveals the difference. The top crops are from the mechanical shutter, while the lower are from the electronic shutter:


What we see here is that the Lumix GH5 has the same image quality using both the mechanical and electronic shutters. The other cameras, on the other hand, lose some details in the shadows in electronic shutter mode, indicating a lower bit depth.

So the Lumix GH5 prioritizes image quality over scan speed, which is why it is the slowest in my above test. Also, it has a higher resolution at 20MP, which slows down the sensor scan.

Keep in mind that these images were underexposed significantly, and then raised in post processing. So the image quality you see here is much worse than what you would get with normal use. In real life use, you would probably not see any difference at all between the electronic shutter and mechanical shutter images, using the Lumix GH4 or G85.

Also, when using a higher ISO, the lower bits are probably mostly noise anyway, meaning that there is little to benefit from the extra bits in the GH5 rendering.

Conclusion


The Lumix GH5 prioritizes image quality over scanning speed in electronic shutter mode. While this will make many fans happy, there is a downside: A slower sensor scan which leads to rolling shutter effects.

Here are some examples taken using the electronic shutter with the GH5. In the first, I pan the camera following the bird, which skews the building in the background:


In the second, a passing car is skewed, due to the speed:


The shutter speed is not relevant for these effects. Even if you set a very fast shutter speed, you would still get the skewing. It is the scan speed which creates these effects, and it cannot be changed. The only solution is to use the mechanical shutter.

But there is good news! If you use the 6K photo mode, then the camera is able to scan the sensor surface much faster, which should help avoiding the rolling shutter effects. It probably caps some bit depth, but as you don't get any RAW file anyway, I guess it doesn't matter much.

Here is the Joker picture taken with 6K photo mode, indicating a scan speed of 1/60s, quite impressive:


Lumix GH5Lumix GH4Lumix G85
Electronic shutter scan speed1/22s1/30s1/25s
Electronic shutter bit depth121010
6K Photo scan speed1/60sNANA
6K Photo bit depth10?NANA

So my conclusion is: If you want to use the electronic shutter and get the best image quality, make sure to keep your camera stable and use the ordinary electronic shutter mode.

If you are going to do actions shots, use the 6K photo mode, which does the same, but with a faster scanning, and without the RAW file output.

The really positive news here is that with the Lumix GH5, Panasonic gives us this choice.

Electronic shutter6K Photo
ProsBest image qualityLess rolling shutter effects, better for sports, animals, etc
ConsCan give skewed effects due to rolling shutterNo RAW output, however, the JPEG image is actually quite good. Be sure to get the exposure and white balance correct when taking the images

Out of the three cameras, I would recommend the Lumix GH5 if you can justify the investment, otherwise, get the Lumix G85. The Lumix GH4 is good for those who must have the V-Log functionality, but want the cheaper option.


9 comments:

  1. I read that Olympus E-M1 mkII has e-shutter speed around 1/60s with raw files. People report there is virtually no rolling shutter effect on moving objects.

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    1. Yes, 1/60s is quite good. Nikon 1 cameras have been at a 1/80s scan speed for years, even with 20MP sensor resolution. And it is enough for most uses.

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  2. I'm curious, what does rolling shutter look like when you use a long shutter speed? I'm thinking something like a timelapse of traffic where you use 1/2 to 1 full second shutter speed.

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    Replies
    1. The amount of skewing would still be exactly as in the example picture above, however, due to the long exposure, there would also be a blurring along the direction of travel. So one would probably not as easily notice the rolling shutter effect, even if it is exactly as with a fast shutter speed.

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  3. Welcome back to blogging Fredrik!

    ReplyDelete
    Replies
    1. Thanks! I have been here all the time, but not too active.

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  4. GH5 needs optional 10bit very fast e-shutter. It would be easy to add because 6k photo already has it. -Vesku

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  5. One GH5 user says GH5 e-shutter is faster with low iso (iso100-iso800 about 1/50s)?
    https://www.dpreview.com/forums/post/59729429

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  6. Very informative post! I like Sigma SD15 for photography as this camera offers best features.

    ReplyDelete