The big question, what to buy? I typically take photos of fast moving kids, nature, the stars, and some time lapse work, so burst mode and an intervalometer are my friends. The tom's hardware review I went to back in 2011 to initially choose the Lexar is still the most current roundup of SDHC cards as of this writing. Of course, in a year, SDHC prices have fallen, especially for the speedier "ultra high speed" UHS-I models. The Sandisk Extreme Pro 16GB UHS-I from the review is now marketed as just a Sandisk Extreme 45MB/s (SDSDX-016G-AFFP) and can be found online for about $18, oddly less expensive than my old Lexar. In terms of camera speed, the metric I was interested in for the memory card was the sequential write speed, and the Sandisk was reportedly 1.74x faster for writes. The SDHC comparison used benchmarks for the computer world, so how does this translate to cameras?
Test equipment:
Panasonic DMC-G3
Panasonic Leica Summilux DG 25mm f/1.4
AC/DC adapter
Intervalometer/remote
Timer
Lexar Professional 16GB SDHC 133x Class 10
SanDisk Extreme 45MB/s 16GB SDHC
Camera setup:
mode: manual
focus: manual
aperture: f/1.4
shutter speed: 1/125
white balance: sunlight
continuous shutter burst, high
format: 4:3, 4592x3448
Quality: JPEG (J), fine JPEG + RAW (J+R) or RAW (R)
Methods:
Memory card was formatted before each test.
For the first burst test, I held down the shutter button using the remote until the buffer filled and counted the number of photos taken. I repeated this three times and took the average of measurements.
For the second burst test, I held down the shutter button using the remote until the buffer filled (7 shots), started the timer, and counted the number of photos taken in 1 minute. I repeated this three times and took the average of measurements.
For the intervalometer test, I set the intervalometer to a 1, 2 or 3 second interval, unlimited shots. I counted the number of pictures taken with the interval over a given length of time. I repeated this three times and took the average of measurements.
Results:
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| Bookshelf. Originally 4.6 MB before rotation. |
Burst test - capture rate (J):
JPEG image size: 4.5MB
Lexar - 9.0 images. Sandisk - 13.0 images.
Burst test - post buffer capacity(J+R):
JPEG image size: 4.6MB
RAW image size: 19.3MB
Lexar - 15.0 images/minute, 5.98 MB/s. Sandisk - 23.0 images/minute, 9.13 MB/s.
Intervalometer test:
JPEG image size: 6.2MB
RAW image size: 19.4MB
| Interval (s) | delta T (min) | theoretical max shots | Lexar (J+R) | Sandisk (J+R) | Lexar (R) | Sandisk (R) |
|---|---|---|---|---|---|---|
| 1 | 1 | 60 | 20.3 | 26.0 | 27.0 | 35.0 |
| 2 | 1 | 30 | 20.6 | 26.0 | 27.0 | 30.0 |
| 3 | 2 | 40 | 35.0 | 40.0 | 40.0 | 40.0 |
| 4 | 2 | 30 | 30.0 | 30.0 | N/A | N/A |
The Panasonic DMC-G3 camera, as well as many cameras, have a "burst" mode to quickly capture a series of photos. The photos are temporarily stored in an internal memory buffer before being written to media. While holding down the shutter button in burst mode, the camera will take as many pictures as it can as fast as it can until the buffer is full. While still depressing the shutter button, subsequent photos are taken when enough memory has cleared from the buffer (i.e., a photo has been written to the media card). Therefore, after the buffer is full, the rate at which photos subsequently are taken is dependent on the speed of data transfer to the memory card.
In the first burst mode test, the Sandisk UHS-I card handily beat the Lexar, capturing 4 more images before the buffer was full. Since the buffer capacity is constant, this means that the Sandisk was able to offload data from the buffer faster, thereby giving more room to acquire more photos in the buffer. No big surprise.
In the second burst mode test, the Sandisk UHS-I card again beat the Lexar, capturing 8 more images per minute. Since we were capturing photos in JPEG+RAW mode, the combined data size per image was 23.9 MB. Based on the recorded transfer rates, 4 and 2.6 seconds per image are required to transfer each photo of this size for the the Lexar and Sandisk, respectively.
In the interval test, values less than the theoretical maximum indicate that the buffer has filled and shots are missed/skipped while space is being made in the buffer for the next shot. The interval data corroborates the second burst test. In JPEG+RAW mode, even up to a 3 second interval, the Lexar cannot empty the buffer fast enough to prevent shots from being skipped, but the card does fine at 4 second intervals. The Sandisk handles 3 and 4 second intervals without trouble, but below 3 second intervals the card cannot keep up with the data. When in purely RAW quality mode, the Sandisk can handle 2 second intervals without filling the buffer, and the Lexar has improved to handle the 3 second intervals. These results point to the Sandisk as having a 9.7-11.1 MB/s data transfer speed, while the Lexar is just 7.5-8.7 MB/s.
We can learn a few things from these results. First, the computer benchmark comparison between the cards translates moderately well to cameras (at least the DMC-G3). In the burst test, the Sandisk card was able to acquire images 1.5x faster than the Lexar. In the interval test, the Sandisk was about 1.3x faster in transferring data. Second, the speed of the Lexar card rather than the camera hardware is limiting the data transfer rate. This may also be true for the Sandisk, but we cannot tell until a faster card is tested or we use other methods.
As an aside, I was hoping against hope that the Sandisk UHS-I card would get me at least one more JPEG+RAW photo in the buffer before capacity was reached (i.e. that one more photo would be written to the card from the buffer) but that was not the case. In J+R mode, I was still stuck with 8 images, but for Fine JPEG only mode, more images could be caught. Of course, a longer shutter speed would increase the time available to write to the card - possibly a benefit for time lapse photography but a burst shutter mode is usually meant for capturing quick action.
Conclusion:
Definitely pick up a Class 10 UHS-I SDHC card versus a standard Class 10. The SanDisk Extreme 45MB/s 16GB SDHC card did not live up to the 45MB/s label, but it was quite a bit faster than the older 133x Lexar and could handle short-interval time lapse photography better. If you need to take a lot of consecutive shots in burst mode, you are better off switching off RAW mode. Either card will handle short bursts in JPEG+RAW, but the UHS-I will allow for quicker, repeated bursts.
