HDSLR: Cheap Compact Flash vs. UDMA

I try to get the best image out of my Canon 7D when shooting video with it. Rumors were going around that using a UDMA high-speed compact flash card may increase image quality, bitrate and decrease the annoying rolling shutter effect. Since I just have used cheapo 133x Kingston CF cards until then, I ordered a SanDisk UDMA CF card with 60MB/s with 8GB – for starters.

The UDMA cards are very expensive compared to “slow” ones – the Sandisk UDMA 8GB is around 50 Euros, a cheap Kingston 133x 8GB is around 18 Euros.
I wanted to test if the investment into UDMA is worth the price. Here are my results: These are movies I shot with my UDMA CF. Roll over the images to see the same image taken with a slow CF.

Image 1: Canon 7D, 70-200mm f/2.8, 1/1000, ISO 800.

Image 2: Canon 5D Mark II, 70-200mm f/2.8, 1/1000, ISO 800.

Here are some screengrabs of the Quicktime inspector showing the bitrate of the original files off the compact flash. Interesting the 7D bitrate was improved slightly when using the UDMA, the 5D bitrate almost stayed the same and even decreased a bit.


Image 3: Bitrate comparison slow/fast CFs with the 7D footage.

Image 3: Bitrate comparison slow/fast CFs with the 7D footage.

Conclusion? In my opinion rolling shutter stayed the same, bitrate didn’t significantly change and color stayed the same. Only thing that is annoying with slower cards is that they need some time to buffer. So when you just inserted the card or started up the camera, push the record button to start buffering. After a few seconds the recording will stop due to buffering issues. After that the recording shouldn’t stop anymore because of that. I say shouldn’t because it happened to me once during an interview shoot. So to be on the safe side, use fast UDMA CF cards for critical shoots.