Tuesday, 31 May 2011

GH2: Buffer flush speed

The Panasonic Lumix GH2 is currently the top Micro Four Thirds camera. Still, it is not a camera with pro features, in my opinion. Of course, there is no firm definition about what constitutes a pro camera. But I would expect to find features like weather sealing, built in remote control receiver, wireless TTL flash control, twin control wheels, all of which are missing on the GH2. Another annoying feature is the slow buffer cleaning speed when using RAW images.

Single exposure

When taking a single exposure and saving both JPEG and RAW images, the delay from taking the image until playback is available is four seconds. I used a SanDisk Extreme Class 10 SD card. See the video below for a demonstration:



As you can see, pressing the PLAY button does not bring up the playback until the buffer has been flushed, which takes four seconds. Without RAW images enabled, this is pretty much instantaneous.

Multiple exposures

Using a fast SD card, the camera can take seven consecutive images in the high speed mode, at 5 FPS, when recording both JPEG and RAW images. But after this, it takes a very long time before you can review the images.

One could speculate that a high quality SD card could be better in this respect than a lesser quality one. I decided to test this, but trying two different cards. Below are two Class 10 SD cards at 8GB each, the premium SanDisk Extreme, and the value Transcend card:


I tested it by putting the GH2 on a tripod, turning off autofocus, and setting the aperture to the max, to avoid any delay caused by changing aperture. I used the Lumix G HD 14-140mm lens.

Here's a video recording of the experiment:



The results speak for themselves. The time from the first picture was taken until the playback was available was: 34.5 seconds (Transcend Class 10), and 24.5 seconds (SanDisk Extreme Class 10).

You can still take more images

While waiting for the buffer to clear, you can still take more images, even if you cannot enable the playback. After the buffer is filled initially, the camera will take one image approximately every third second. So this is not such a huge problem as it may seem like.

Here is a demonstration:



Auto review

Even if you cannot enable playback until some delay, the camera can still show a quick preview after capturing the image. This feature is called "Auto Review". You can find it in the "Setup" menu:


The Auto Review is a simple playback, and does not allow zooming in, for example.

Conclusion

The result surprised me. I was expecting to find that a Class 6 card is sufficient for use with the GH2, and that any faster card is a waste of money. Quite to the contrary, I find that using a more expensive premium Class 10 card actually has some real benefit, when recording RAW images.

Another conclusion is that even with a high end SD card, the buffer flush delay is significant with the GH2. 24 seconds is a long wait. Of course, when taking many exposure one could consider to turn off RAW recording, which would solve the problem.

The Panasonic GH1 has also got a slow buffer clearing speed. I haven't tested them head to head, but they feel pretty similar.

If you only use JPEG images, you don't get these significant buffer clearing times. In that case, you can basically ignore this test.

So do you need to use RAW? I find that if I have a good exposure and the correct white balance, I can use the JPEG image straight from the camera with no problem. But if the exposure is tricky, or the white balance is off, then having the RAW file comes handy for getting the best results. So for low contrast images at daytime, using RAW has little benefits, I'd say.

7 comments:

  1. How fast can you write to the cards if you connect them to your computer using a card reader?

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  2. Excellent, even-handed description of gh2 behavior.

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  3. I did a recent comparison myself with the GH2: http://forums.dpreview.com/forums/readflat.asp?forum=1041&message=38752119

    Quoting some of it here:

    Burst shooting, RAW format, 7 shots
    Three different SanDisk Extreme SD cards

    Timing how long from the shutter press to the "writing to flash indicator" goes off

    1) SanDisk Extreme III 30MB/s SDHC C6 16GB = 22s
    2) Sandisk Extreme 30MB/s SDHC C10 16GB = 23s
    3) SanDisk Extreme Pro 45MB/s SDHC I U1 32gb = 22s

    The Class 6 versus Class 10, and the 30MB/s versus 45MB/s does not appear to have any measurable difference on the GH2 shooting RAW in burst mode.

    All tests run multiple times. All with the same lighting and 20mm Panasonic lens. All with freshly wiped (i.e. "delete all photos") SD cards.

    My advice from this simple test: The "Pro" card isn't worth it for the GH2, because the lag to flush the buffers to the card appears to be in the camera, and not between the camera and the SD card.

    (Obviously, there may be benefits for video, or other types of shooting.)

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  4. Which one is faster for a finepix hs 20.

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  5. I don't understand that question.

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  6. Very nice analysis. I thinnk I will buy the class 10 even if not necessary because I seem to keep memory cards longer than I keep cameras (LOL) and the class 10 might be better when and if I buy an upgrade in the future (GH3?)

    Peter F.

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  7. The point in getting the Pro is to allow for shooting higher bit rate hacks. My 30MB/sec card can't handle certain hacks, but the Pro can. Plus the 16GB Ext Pros are like $13 now at Frys.

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