Published: May 5, 2015
The Canon Rebel T6i and T6s (750D/760D) cameras are a major update to Canon's entry level EOS Rebel DSLR. The T6 cameras offer a 24.2MP megapixel APS-C sensor, an upgrade over the 18MP sensor found in the T5i (700D). The AF system has been improved to 19 cross-type sensors in addition to on-sensor phase detection. The T6i/T6s use the DIGIC 6 image processor and are capable of up to about 5 frames per second in continuous shooting. A single memory card slot accepts standard SD, SDHC and SDXC memory cards and supports UHS-I.
Write speed and continuous shooting performance were tested using a total of 52 SD cards. Both the T6i and T6s were tested and the results were essentially the same in both cameras. The following results are for the T6s. The write speed results are provided for RAW images. The continuous shooting results are provided for RAW+JPEG, RAW and JPEG image modes. After the results an analysis has more details and observations from the tests. Recommended SD cards for the T6i/T6s are provided for the fastest write speed and best value.
When testing the T6i and T6s an unusual result was observed. In most cameras the write speed during continuous shooting for a given memory card is usually similar when shooting different scenes and is only slightly affected by file size (smaller files typically reduce write speed slightly). When the T6s and T6i were tested using a detailed test scene that created large files (33.7MB RAW) the average write speed was around 49MB/s with the fastest card, while a less detailed scene averaged 74MB/s write speed (26.5MB RAW files). Tests with the lens cap on (22.2MB RAW files) averaged 71MB/s write speed. Shooting detailed scenes can reduce the in average write speed of the T6i and T6s. All cards were affected by this reduction, not just the fastest ones. The camera is probably not writing continuously or at its highest rate when it processes large, detailed images.
For these tests the camera is mounted on a tripod and focused on a static test scene under controlled lighting. The test scene used is of average detail. (This differs from other tests that use a detailed scene because the T6s/T6i write speed was limited when using highly detailed scenes.) The camera is operated by a remote timer that provides 30 second intervals.
Write speed is determined by a new method that eliminates the use of the card access light. Write speed is the rate at which the buffer clears after the buffer has reached capacity. The buffer full condition begins when the buffer has reached capacity and is unable to sustain the full frame rate. The first shot at the lower frame rate until the last shot is the time interval used (range 25.8 - 28.4 seconds). The total bytes written is the number of shots during this interval (less one since the beginning and end are determined by shots) multiplied by the average file size (recalculated for for each card). Comparing results using the new method to the method using card access light shows the access light consistently adds about 0.7 seconds (resulting in about 2.2% lower apparent average write speed). While the access light provides a consistent and easy measurement, it is illuminated as soon as the shutter is first activated, not after the first shot is processed and written.
The continuous shooting test measures the number of images taken in 30 seconds. Three image modes are used for this test: RAW+JPEG, RAW, and JPEG. The JPEG setting is large, fine quality. The Canon T6s is set to continuous high release mode. The subject is a test scene of average detail (with this camera the write speed is limited when using highly detailed scenes). The average RAW file size is 26.5 MB, average JPEG file size is 6.2 MB.
The Canon T6s/T6i can use UHS-I SD cards, and support the fastest SDR104 bus mode. While many Canon cameras support UHS-I, only recently have they supported SDR104. Earlier cameras such as the Canon 6D and 70D do not support SDR104 and are limited in write speed. The Canon 7D Mark II also supports SDR104. It and the new Rebel T6i and T6s support higher SD card write speed than most previous Canon cameras (excluding those that support CF cards).
The T6s and T6i both have a relatively small buffer. The term "Buffer capacity" usually means the number of shots before the frame rate slows. In this definition it is not a static number, but can change depending on the write speed of the card, the subject of the shot (file size) and camera settings. In these tests the buffer capacity ranged from 6 to 7 shots RAW+JPEG, 7 to 9 shots RAW, and 23 to infinite JPEG. This range is due to different SD card write speeds; faster cards allow more shots at full frame rate because they clear the buffer faster during continuous shooting.
Card write speed affects the frame rate when the buffer is full. In these tests in RAW+JPEG mode, frame rate with the buffer full varied from 0.4 to 1.6 fps, depending on card speed. RAW frame rate varied from 0.4 to 2.8 fps. JPEG was 1.6 to full frame rate (4.7 fps). In addition to the card write speed, frame rate depends on camera settings and image subject. The subject in this test created 26.5 MB average RAW files and 6.2MB average JPEG files. (This subject differs from the detailed subject used in earlier camera tests so these results should not be used to compare different cameras. This information is provided to illustrate the difference between memory cards in this camera.)
The fastest SD cards for the Canon T6s and T6i are the SanDisk Extreme Pro 95MB/s UHS-I 64GB SDXC Card and Lexar Professional 2000x UHS-II card. Both cards performed at 73.8 MB/s average write speed during continuous RAW shooting. The T6i and T6s only support UHS-I. In these cameras UHS-II cards operate in UHS-I mode and offer no write speed advantage. However in a UHS-II card reader the UHS-II cards offer much faster download speed. The Lexar Professional 2000x UHS-II card averaged around 250 MB/s downloading images to a computer. The Extreme Pro 95MB/s UHS-I card is no slouch either, it provided 90MB/s download speed. It should be noted the SanDisk Extreme Pro 280MB/s UHS-II card was much slower in UHS-I mode, only reaching 41.1 MB/s average write speed (the card does not support the faster UHS-I mode SDR104).
There are many cards that offer high write speed at a relatively low cost. One example is the Kingston Class 10 64GB SDXC card (SDA10/64GB), which is a "second tier" card but offers nearly the same write speed as the fastest cards in the T6s (note the 32GB capacity card did not provide the same write speed). Depending on price the Samsung PRO SD cards offer fast write speed (both 32GB and 64GB cards averaged 69MB/s) and frequently go on sale at Amazon.
The T6s and T6i have a USB 2.0 port on the camera that can be used to download images. Using the SanDisk Extreme Pro 64GB SDXC card and copying 3GB of RAW images from the camera to a computer with a SSD drive, the transfer averaged around 31MB/s. This is good performance for USB 2.0, but well short of what can be achieved with a USB 3.0 card reader. In a separate USB 3.0 card reader, UHS-I cards such as the SanDisk Extreme Pro 95MB/s provide actual download speeds of about 90 MB/s. UHS-II cards like the Lexar Professional 2000x UHS-II can reach around 250 MB/s when copying actual RAW files. Further card reader tests and benchmarks can be found in the Card Reader Reviews.