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May 20, 2008

Shooting Raw Images with the Canon EOS 40D

OK, so my buddy Brian has convinced me that i need to be shooting Raw images with my Canon EOS 40D, instead of just shooting JPEG's which is what I had been shooting. Of course, ideally, what I'd like to shoot is RAW and JPEG, which is what I've been shooting lately, but now disk space and data transfer speed of the camera and the CF card become more critical. Brian asked me how shooting Raw + JPEG would affect the speed of the camera, so I decided to do some benchmarks.

On the website DPReview.com, to test how many frames a camera can shoot in a second, they hold down the shutter release button and make audio recordings of the camera. When you edit the audio recordings, you can then clearly see the shutter releases as a series of sound waves. So, I decided to do a similar test here in my home studio.

For the test, I wanted the camera to be very steady, with the auto-focus turned off, and a relatively fast shutter speed so that the camera could focus on taking as many shots as possible, without worry about waiting for a focus lock or waiting for the shutter to release, etc.

Additionally, I wanted to capture an image with a reasonable amount of detail, as opposed to shooting say, a white wall, as the .JPG files will be larger if there is more detail in the photo.

To perform the test, I used a Canon EOS 40D with a SanDisk 4GB Standard CompactFlash® Card.

For the lens, I used an mage stabilized, ultra-sonic telescopic zoom lens (EF-S 17-85mm f/4.0-5.6 IS USM). I mounted the camera and lens on an Italian Bogen - Manfrotto tripod with a Bogen - Manfrotto 3265 Grip Action Ball Head with Quick Release. Once the camera was stabilized, I connected the Canon RS-80N3 Remote Shutter Release so that I could trigger the camera without touching the frame.

I pointed the camera at a subject with some color and detail, to ensure that the .JPG files would be a reasonable approximation of normal shooting conditions.

Then I set the focal length on the lens to be a "normal" lens (50mm), and measured the distance to the subject (approximately 26"). I turned on the auto-focus, and allowed the camera to lock in, then turned the auto-focus off so that the camera wouldn't try to "hunt" for an auto-focus lock during the test.

I wanted a relatively fast shutter speed, so I set the film speed to ISO 1000 and the aperture to f/6.3 and the shutter speed to 1/100 sec. I calculated the Depth of Field to be approximately 2.4".

Then, I went into the camera's setup menu and reformatted the CF card and configured the camera to shoot only large JPEG files.

To record the sound of the camera's shutter, I used an M-Audio SoundCheck microphone connected through an M-Audio FastTrack Guitar/Microphone recording interface to an Intel Core 2 Duo 6600 @ 2.4Ghz computer running Windows XP Pro SP2 with 2 Gig of RAM.

For the recording software, I used Audacity version 1.2.6.
For a timer, I used Online Stopwatch.

The Canon EOS 40D has two continuous shooting drive mode speeds - High Speed (6.5 fps) and Low Speed (3 fps). After some experimentation, I decided to do three 30 second "High Speed" tests where I'd hold down the remote shutter release for 30 seconds in three different resolution modes: JPEG(.JPG), Raw(.CR2), and JPEG + Raw (.JPG + .CR2).

The results of the High Speed 30 Second Tests are as follows:

Test 1: Large JPEG(.JPG) files only. In 30 seconds, the camera captured 68 photos. Each image was recorded as a JEPG file of approximately 3.73 MB, for a total of roughly 253 MB. In this test, the camera captured 57 frames in under 9.5 seconds, and then 11 more frames at the rate of one frame every two seconds after the buffer filled up.

Test 2: Raw (.CR2) files only. In 30 seconds, the camera captured 22 photos. Each image was recorded as a Raw file of approximately 11.9 MB, for a total of roughly 262 MB. In this test, the camera captured 17 frames in under 3 seconds, and then 5 more frames at the rate of one frame every five seconds after the buffer filled up.

Test 3: Raw (.CR2) + Large JPEG(.JPG). In 30 seconds, the camera captured 18 photos. Each image was recorded as a Raw file of approximately 11.9 MB, and a JPEG file of approximately 3.7 MB, for a total of roughly 282 MB. In this test, the camera captured 14 frames in under 2.5 seconds, and then 4 more frames at the rate of one frame every seven seconds after the buffer filled up.

So, what we see in all three of these tests is that, once the buffer fills up,shooting slows down dramatically, as the weakest link in the chain is the speed that the camera writes data to the CF card. By my calculations, the data is being written onto the CF card at about 2 - 2.3 MB/sec. So, this is painfully slow.

Basically, what it looks like is I need to get me a faster CF card. Maybe something like this.

Part II

Buffer size

The buffer is the in-camera memory used to store images before they get written to the CF card. The buffer is high speed memeory, while writing to the card is a somewhat slower process. The 40D buffer can reportedly hold 75 large/fine JPEGs (the highest quality JPEGs) or 17 full size RAW files.

Based on my tests, I calculate the buffer size on the EOS 40D to be somewhere in in the neighborhood of 200 MB - 220 MB. Once that high speed buffer fills up, then the camera can't shoot until at least some of the data is written from the buffer to the CF card.

According to DP Review, the fastest speed at which the EOS 40D can write data from the buffer to the CF card
is about 7 MB/sec. "...with the best performing card (the SanDisk Extreme IV) we get over 7 MB/sec for both RAW and RAW+JPEG formats."

So, if the camera is capable of writing data to the CF card at 7 MB/sec, and my own benchmark tests with my CF card indicate a performance metric of closer to 2 MB/sec, then it would seem that there is some room for improvement. In theory, I should be able to buy a faster CF card and see an improvement in my continuous shooting tests.

What I have is the SanDisk Standard blue CF card, which is kinda gay. Not really my style. But which card to buy? The SanDisk Extreme IV? SanDisk Extreme III? SanDisk Ultra II?

Here are the speeds of the cards advertised by SanDisk.
SanDisk Ultra II "...15MB/sec Read/Write speeds"
SanDisk Extreme III "...an amazing minimum 20MB per second** sequential read and write speed (**Based on SanDisk internal testing)"
SanDisk Extreme IV "...extremely fast read/write speeds. (Up to 40MB/sec*) (*Based on internal SanDisk testing.)"

This website has a pretty meticulous comparison of the read/write speed of various CF cards.

This guy says he's shooting a 30D and a 40D, and that the way to go is the Extreme III:

"With a 40D, it can read and write at full speed with a III card. The only advantage of the limited capacity, more expensive IV cards with the 40D is that it is faster in card reader transfer speed, as the 40D does not support the new in camera transfer dynamics of thr Ext IV series cards."

I can pick up a SanDisk Ultra III 8 GB CF card for about $100.00, so maybe I'll pick one up.

Posted by Rob Kiser on May 20, 2008 at 9:54 PM


Where are you getting an 8GB Ultra III for that price? The closest price I've seen to that is an Ultra II for the same price, down at MicroCenter in the DTC. I haven't looked at ordering one online yet - I was looking for an emergency backup card yesterday since I had to shoot some sports stuff and I only had a 1GB card with me, which will only hold about 220 pictures.

Shooting with an Ultra II I haven't had my Digital Rebel XTi seize up from the buffer filling up while I've been the burst feature, but then, I'm not shooting in Raw.

Did I mention I'm jealous of your toy? I just got my XTi less than a month ago (my hubby ROCKS), and I'm already eagerly awaiting the GPS coordinate feature Canon's supposed to be adding in a year or so. So I can't quite justify going out and buying a new camera just yet.

Posted by: Alice H on May 25, 2008 at 1:10 PM

Oh, and obviously the 40D's going to have a faster burst rate.

Posted by: Alice H on May 25, 2008 at 1:12 PM

Yeah, that's the problem with the digital SLR's vs. film cameras. The digital cameras depreciate, whereas the film cameras held their values. So, buying a digitial camera is more like buying a computer, unfortunately. A state-of-the-art Canon digital SLR you buy this year is worth next to nothing in 3 years. Sucks. As for the CF card, I just googled it and that was what the cards were going for. I use PriceGrabber sometimes if I can't find it in Google though.

Posted by: Rob Kiser on May 27, 2008 at 2:43 AM

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