Tech Tips
August 2009

by Chuck Westfall

Q: Many a sports photographer switched to Canon [in the 1990s) because at that time their AF lenses were considered fastest. I think this may still be the case but wonder why [there is] no publishshed spec data on how fast these lenses focus. Other brands do not publish these specs either. Why is that?

A: That's a good question. Perhaps the best answer is that a pure lens drive speed specification isn't very meaningful on its own. There can be differences in lens drive speed when the same lens is used on different cameras, or even on the same camera, as battery charge levels drop during the course of a game. Moreover, a complete AF sequence always consists of focusing calculations as well as lens drive. When it comes to focusing calculations, there are a lot of variables that affect AF speed, such as light levels, subject contrast, subject distance vs. lens focal length, subject speed and movement patterns, etc. Beyond the technical considerations of lens drive speed and AF performance, a professional sports photographer must also choose the right lens for the job. For instance, it may be true that a 300/2.8 lens autofocuses faster than a 400/2.8, but that doesn't mean much if you need the 400mm lens to make the shot.

Q: I am looking for the fastest memory cards the EOS 50D can take advantage of. For example, SanDisk® Extreme® III cards can be read and written at 30MB/s or 200x speed. SanDisk® Extreme® IV cards can be read and written at 45MB/s or 300x speed. I know these are quality cards. Given this example, if the 50D only reads/writes at 25 or 30MB/s I get the same results from either card so I can buy the Extreme® III cards and save some money. If, however, the 50D reads/writes at 40 or 50MB/s then the Extreme® IV cards are well worth the extra cost. So, concisely, at what speed does the EOS 50D camera read/write? Alternatively, what were the entire specifications of the 2GB card used in Canon testing for burst rates? Please advise me.

A: The EOS 50D and 5D Mark II cameras are compatible with UDMA CF cards up to UDMA Mode 6, which represents a data transfer rate of 133 MB per second. That's megabytes, not megabits. Nobody is selling Mode 6 cards yet, but the 50D and the 5D Mark II will be ready when they do. Canon does not publish a specific speed rating for data transfer with EOS cameras, but you can find reliable independent test results on the Web. I would suggest checking Rob Galbraith's CF/SD database here:

From this, you can see that the 50D's effective throughput is less than the full speed rating of the Extreme IV cards (approximately 33MB per second vs. 45MB per second), but Canon anticipates that the camera will write data faster when faster UDMA cards show up on the market.

Q: While Canon's E-TTL II provides superb fill in and balanced lighting, it's also vulnerable to reflections and hot spots. As a wedding photographer, I'm always looking for a "sure-fire" way to obtain an acceptable exposure quickly especially when time is critical. With the bride coming down the aisle, I don't have the time for a trial and error FEC (flash exposure compensation) or for her dad to hold an 18 percent gray card while I do an FEL (flash exposure lock). Flash [exposure] bracketing is risky because the bride is moving. Some claim that diffusers help (I have the LumiQuest 80/20 and Gary Fong Lightsphere) but an unexpected metallic handbag, white dress or white shirt in a dark church has ruined a lot of important shots! Also, I've searched for an advanced class book on E-TTL II but haven't found anything except for a couple of very cursory books that offer little more than what is on Canon's technical help Web pages, the best of which is in Europe …. Any suggestions?

A: Before answering your questions, I have some questions for you:

  1. For your processional shots and other indoor flash photos, what's your typical ISO setting? How about aperture and shutter speed?
  2. Which flash metering pattern are you using, evaluative or average? I am not talking about the ambient metering pattern set on top of the camera.
  3. Are you willing to use a diffuser like the Fong sphere or similar?

Q: Thanks for the reply and I appreciate the help. I know I'm doing something wrong and I'm determined to get to the bottom of this problem.

  1. I generally shoot at ISO 400 and generally in the Av mode, if not, manual. With my new 5D II, I'm slowly starting to trust the new ISO Auto selection. In Av, I set C.Fn I: (Exposure):7 at 1 (1/200 - 1/60 sec. auto) unless I have some difficult ambient light issues. Apart from full Auto and Creative Auto, I have worked with the other modes on the 5D II. Depending on ambient lighting, depth of field and distance, I usually work with an aperture range from wide open to f/8. I'm using the Canon EF24-105mm f/4L IS USM "kit" lens, which, in my opinion, is a superb piece of glass. My usual flash is the Canon 580EX II.
  2. The reflection/underexposure problem I'm encountering seems to occur with the flash metering set for either Evaluative or Average. I use both. I find with white table cloths, white shirts, white wedding dresses, etc., that Average sometimes seems to be more forgiving but other times Evaluative works best even though both modes will be 1/2 to a full f/stop dark.
  3. I do use the Gary Fong Lightsphere Diffuser. Specifically, the new Universal "Half-Cloud" (same material as the "Clear" model). I like the results and I think it's better than the LumiQuest diffuser most of the time ... but ceilings and room vary so there are no hard rules. There's more than enough power in the 580EX II to handle the diffuser.

My current solution to the under-exposure problem is to simply pump the flash exposure compensation by about +1 to 1-1/3 but then kick and scream when I blow out a shot after forgetting to reset the FEC. Again, do you have any suggestions? Is there an ETTL-II textbook that you can recommend?

A: Thanks for the clarifications. It gives me a better idea of your workflow, even though I haven't seen any of your problem images. Based on your answers, here are a few suggestions that might be helpful:

  1. Consider using a higher ISO for your indoor shots. I think this step alone would go a long way towards minimizing your exposure issues. If you're at ISO 400 and f/8 with a Fong sphere, you may be pushing your 580EX II harder than needed. I could understand those settings for a group shot to help you maintain sufficient depth of field for several rows of people, but not necessarily for processionals or typical reception photos of couples or small groups. The multiple benefits to ISO 800 on your 5D Mark II for indoor flash shots would outweigh any perceived disadvantage in terms of noise. For example, you'd get a better exposure of the background areas that are not illuminated by the flash, and you would also get faster recycling in addition to more flashes per set of batteries.
  2. Consider using a Compact Battery Pack CP-E4 or equivalent. In addition to eliminating recycling delays, this would also tend to make your flash exposures more consistent.
  3. Stick with Average flash metering for your indoor flash shots, and expect to apply about a stop or so of flash exposure compensation when there's a lot of white material in the composition (table tops, bridal gowns, etc.). Evaluative flash metering is at its best for outdoor fill-flash shots, whereas Average usually works best indoors.
  4. Consider registering your indoor settings and your outdoor settings to separate Custom modes on your 5D Mark II. This would make it quicker and easier for you to switch the camera to the optimum settings when you move from one set of lighting conditions to another. For instance, C1 could be your outdoor fill-flash setup with a low ISO and Evaluative flash metering; C2 could be your indoor flash set-up with ISO 800 and Average flash metering.
  5. Don't forget that your 5D Mark II/580EX II combination can be adjusted very easily through the External Speedlite Control menu on the camera's 3-inch LCD screen.

Canon really doesn't publish much advanced information about E-TTL II flash photography beyond the content you mentioned on the CPN Web site, but there are some independent sources worth checking out:

Q: Thanks very much for the very useful information. You have pretty much confirmed that I'm on the right track but I just need a little fine-tuning. I've used battery packs in the past but the wire makes me feel a little off-balance. I still use a flash bracket so I've got the curly cable to contend with. (Do you mount your flash on a handle/bracket? ... what make/model?) In addition to your suggestions regarding a higher ISO, Average vs. Evaluative flash metering and moving the FEC up a bit, I'm also hedging my bet by shooting most flash shots in RAW which allows me to adjust for problems after the fact even though the shooting time can be delayed and post processing time can take half of forever! Thanks again for your suggestions and links.

A: No problem, I'm glad the information was helpful. I don't use a flash bracket these days, but I know several professional wedding photographers who do. Brackets can get heavy, but they're great for positioning the flash above the camera and pointed down just a bit to control the direction of the shadow. You might want to check out some of the products from Custom Brackets:

I like the way they let you flip the camera from vertical to horizontal without changing the position of the flash. There's also enough room on the bracket to mount an external battery pack so you don't have to contend with wires connected to your belt or vest.

Q: I use my EOS digital cameras for unusual photography (flying bats, star trails, etc.) and am wondering if long exposures or keeping the camera running for long periods (three hours) can damage the CMOS sensor or other parts of the camera. I used three of my cameras the other night and after several hours of use in the hot Arizona desert they failed to take some images. Could I have done some long-term damage????

A: Long exposures pose no threat to the longevity of Canon's CMOS sensors in EOS Digital SLRs, but they will run the camera's battery down. If the battery voltage falls below a prescribed limit, the camera will shut off and any image data in the buffer memory will be lost. I've commented on this topic several times in previous editions of Tech Tips, most recently in November 2008. Here is a relevant excerpt:

"Realistically, maximum bulb exposure time for an EOS Digital SLR is going to depend on the type of power supply and to some extent the ambient temperature conditions. By far the longest exposures are enabled when using the optional DC Couplers and AC Adapter Kits, since these accessories eliminate concerns about battery life. If you're doing astrophotography from your backyard or any other location where AC power is accessible, this is probably the most feasible solution. When AC power is not accessible, the next best solution is to use an optional battery grip and load it with two lithium-ion rechargeable battery packs. The battery grips and battery packs will vary according to the camera model involved, but in moderate temperatures it would be reasonable to expect no more than approximately 4 to 6 hours of battery life for time exposures with a two-battery power supply. In situations where only one battery pack is available, the total bulb exposure time in moderate temperatures will be somewhere in the range of 2 to 3 hours. Cooler temperatures down to the cameras' minimum rated operational range of 32 degrees Fahrenheit will reduce battery life somewhat. In answer to your second question, any image data in the camera's buffer memory will be lost if the camera loses power before the file is written to the memory card. Since long exposure noise reduction in the camera can last as long as the actual exposure, you'll need to factor that into your decision on setting the length of time exposures."

Thanks for reading Tech Tips! That's it for now. See you in September!

You are invited to submit questions about photo equipment, imaging technology, or photo industry trends that may have a bearing on your work or interests. I cannot promise to answer all inquiries, but I pledge to do my best to address the issues that concern you. (Please use the e-mail link provided at the end of this article.)

P.S.: The purpose of the Comments section is to allow readers to respond to the content of each month's edition of Tech Tips. New topics or questions should be submitted by e-mail (using the link at the end of each column) in order to support the development of future monthly editions. I appreciate your kind support and cooperation. Thanks!

© Chuck Westfall

After earning a degree in Professional Photography from the Rochester Institute of Technology and accumulating some valuable on-the-job experience during a 10-year stint in commercial photography and photo retail, Chuck Westfall began his corporate career with Canon U.S.A. in 1982 as a Technical Representative. He has steadily advanced through the ranks to achieve his present position as Technical Advisor for the company's Consumer Imaging Group, working out of Canon U.S.A.'s headquarters office in Lake Success, NY. Among his many assignments, Chuck Westfall is currently Canon USA’s main media spokesman for new camera products. He also provides a unique insider’s perspective to financial analysts who follow the company’s CIG sales and marketing activities.

Chuck’s involvement with digital cameras began in 1994, when he assisted Canon and Kodak engineers in developing the EOS-DCS series of professional SLRs. Since then, his responsibilities have expanded to include participation in the development and launching of many other Consumer Imaging Group products including Canon's professional and consumer-oriented digital cameras. Most recently, he has been developing content for online and on-site consumer education projects in Canon USA’s Professional Products Marketing Division.

On the personal side, Chuck enjoys sightseeing, photography, reading, music, and family life with his wife Ying and their beautiful daughter Anna.

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