Tech Tips
November 2009

by Chuck Westfall

Q. I have just taken delivery of an EOS 7D, which has staggering performance and functionality for the price, along with the delightful (at last) fact that the BG-E7 grip has an AF-On button!!! I have been using the on-board flash in lieu of the ST-E2 wireless controller, which is super convenient, but I am finding that I don't get the rapidity of recycling that I can achieve otherwise. Is this because the on-board flash is sending out a pretty hefty pre-flash, and then needing to recharge? I was doing some high-speed flash work with several 580EXs dialed down to 1/16th power. When I hook these up to Pocket Wizards and Quantum Turbos, I can generally get a 10- or 12-frame burst at full speed on my 40D. Using the 7D on-board flash, I can only achieve about 3 frames on the 7D. I will do some more exhaustive tests in the lab tomorrow, but thought you may have some quick insight?

A. Adding wireless control features to the EOS 7D's built-in flash is a great new feature, but one of the definite trade-offs is slower recycling than an ST-E2 or 580EX II. Over half of the built-in flash's capacity is used just for firing the preflash that's used to control the off-camera Speedlites. Despite this limitation, you can usually fire off several shots in a burst, but after that you'll need to wait a few seconds for recycling to finish. To make the most of the built-in flash's limited capabilities, I would suggest the following:

  1. Use higher ISOs, moderate apertures and short camera-to-subject distances to reduce the amount of light needed for a correct flash exposure, or disable the built-in flash in a multiple flash set-up. (In this case, the built-in flash will still fire a pulsed preflash to control the off-camera Speedlites.)
  2. If you need to shoot rapidly, consider using the 7D's 3 fps Continuous setting as opposed to the 8 fps High-Speed Continuous setting.
  3. Consider loading two LP-E6 batteries into your BG-E7 to increase the number of flashes you can fire before recharging the batteries.

Q. My question is specifically about the EOS 7D, but it could be generalized to any other time Canon has introduced a new AF system. Is there a definitive list anywhere of exactly how compatible the AF assist beams on Canon's various current and discontinued flash units are with this body's AF system? I'm currently using a 420EX with my 20D, and while the AF assist isn't perfectly matched, it usually works well enough in practice. But in planning for my upgrade to a 7D in a few months, I have yet to find any discussion anywhere of whether this, or any other, flash (including the current 430EX II and 580EX II) provides full AF assist for all of the 7D's points and the various other AF settings like AF zones. This makes it hard to plan on whether I can get by with just a body upgrade or if I have to budget hundreds of dollars more for a new flash as well, and if so, whether I have to go all the way up to a 580 or if the 430 would provide proper AF assist. Thanks in advance for any pointers you can provide.

To the best of my knowledge, Canon hasn't published any detailed information about the coverage of the AF Assist beams from various EX Speedlites with the EOS 7D camera. However, based on my own testing, I can confirm that Speedlite 580EX II's AF assist beam covers all 19 of the EOS 7D's AF points at focal lengths down to 15mm. (I tested with the EF-S 15-85mm lens.) Speedlite 430EX II's AF assist beam covers 15 out of the 19 AF points on the EOS 7D at 15mm, but all points are covered at focal lengths of 70mm and up. The AF points that don't get coverage at wider angles with Speedlite 430EX II's AF Assist beam are positioned to the left and right of the vertical center line in the row below the horizontal center line (2 to the left of center and 2 to the right.) The corresponding AF points above the center line are covered, even at 15mm, because Speedlite 430EX II's AF Assist beam coverage is slightly asymmetrical with respect to the EOS 7D's 19 AF points, i.e., it provides more coverage above the center line of AF points than below it. So the 580EX II is the best performer in this comparison, but the 430EX II will probably be fine for the vast majority of shooting conditions. Now that the EOS 7D is available through dealers, you can try it for yourself to see if it meets your needs.

Q. Can you explain the difference between the camera's standard fastest flash sync, and High-Speed sync?

A. You can see a very good illustration of the technical difference between standard electronic flash operation and Hi-Speed sync on this Web page:

In a nutshell, the flash fires in a single burst during standard operation vs. firing continuously at roughly 50,000 cycles per second in Hi-Speed sync mode. The advantage of standard flash operation is potentially greater light output levels, but the disadvantage is that shutter speeds are usually limited to the maximum X-sync speed of the camera, i.e., the fastest speed during which the image sensor or film is fully exposed to light at the same time during an exposure. With focal plane shutters, higher speeds are accomplished by causing the second shutter curtain to follow the first curtain before the first curtain has completed its travel, thus creating a slit that moves across the image sensor or film during the exposure. Standard flash operation is not effective at high shutter speeds because the image sensor is always partially blocked by the shutter during the exposure, thus creating an uneven lighting effect. Hi-Speed sync gets around this problem effectively by turning the flash into a constant light source. The disadvantage of Hi-Speed sync, if you want to call it that, is that the maximum output of the flash is at best approximately half that of standard flash operation, and the effective output drops progressively as the shutter speed increases. This factor limits the usable distance range during Hi-Speed sync, making it primarily effective for portraiture, macro, and other close-range subjects. Nevertheless, within its usable range, Hi-Speed sync is a tremendously useful creative tool. Not only does it allow the use of large apertures for shallow depth of field, it also allows a great deal of control over ambient exposure levels. One of the best ways to take advantage of this feature is to underexpose the ambient light, thereby drawing the viewer's attention to the subject that has been accurately exposed by the flash.

Q. What would the practical consequences be of lower sync speeds as a standard, assuming one has a flash with High-Speed mode?

A. The lower the sync speed, the smaller the aperture that must be used to achieve an

accurate exposure of the ambient light in a brightly lit environment. The smaller the aperture, the greater the depth of field and the shorter the usable flash-to-subject distance range. Hi-Speed sync effectively returns creative control to the photographer, because shooting flash photos in a brightly lit environment at high shutter speeds allows the use of wider apertures to reduce depth of field.

Q. Also, is there a disadvantage to leaving the flash in High-Speed sync mode all the time?

A. It depends on the camera. In most cases, there is no disadvantage to leaving the flash in Hi-Speed sync mode all the time because it doesn't kick in until the shutter speed goes higher than the maximum X-sync speed. But if you are using an EOS 5D Mark II or 5D camera, Hi-Speed sync can kick in at maximum X-sync speed (1/200 with those cameras.) If you want full power from your flash at 1/200, be sure to shut off Hi-Speed sync with those camera models.

Q. I believe my 1D had 1/500 standard sync. 

It did, because of its interline transfer CCD image sensor. With that camera model, the focal plane shutter never fired faster than 1/125, and higher shutter speeds were controlled directly by the image sensor. All other EOS Digital SLRs use CMOS sensors which cannot control their own shutter speeds for conventional still photos. For still photos, the shutter speeds of all EOS Digitals with CMOS sensors are controlled either partially or completely by their focal plane shutters, thus their maximum X-sync speed never gets higher than 1/200, 1/250 or 1/300 depending on the camera model and flash unit in use.

Q. I've just discovered Hi-Speed sync, but there's one thing I can't figure out. If I put my 580EX II into manual mode, say 1/32 power, and my EOS 5D into Av mode, it shoots at 1/8000 every time! Is this supposed to happen?

A. The issue here is the combination of a Manual flash setting with Aperture Priority on a relatively older EOS camera. Hi-Speed sync is not directly involved. If you had used an EOS-1D Mark III, 40D or any other EOS model introduced since 2007, and set up the camera and flash the way you describe, the shutter speed would have been set by the camera to expose the ambient light properly. But, with any EOS camera introduced before 2007, including the original 5D which came out in 2005, manual flash settings should not be used in either Av or P modes. If you try to do so, the camera will set the shutter speed to either maximum X-sync if High-Speed sync is turned off, or the fastest shutter speed on the camera if High-Speed sync is turned on. This is what happened to you. If you stick with your original 5D, there are two alternatives to consider.

  1. If you want to use Manual flash, you need to set the camera to Manual mode as well.
  2. If you need to set an AE mode on the 5D, such as Aperture Priority, you need to set the 580EX II to E-TTL mode, i.e., automatic flash exposure.

Both methods will work with or without Hi-Speed sync. If you update your camera to any EOS model introduced since 2007, then you can combine Manual flash settings with AE modes on the camera.

Q. I was just asked to shoot a time lapse of our local stadium stage set-up and teardown (they want to be able to show clients how everything can be changed easily). Apparently, it will take all night (and I'm not sitting there for 10 hours to keep pushing the shutter release). Could I make this work using Canon EOS Utility software and a 5D tethered to a laptop? Is there a way to connect the 5D to a power source so the battery doesn't die? Once I have all the images, what software could be used to produce the movie?

A. EOS Utility does in fact support intervalometer functions during tethered operation with any compatible EOS Digital SLR including the 5D. Once you have the camera set up and connected, look for the clock face icon in the middle of EOS Utility's remote shooting menu screen on your computer. Click on the icon to display the intervalometer settings menu and take it from there. The EOS 5D can be connected to AC power via the optional AC Adapter Kit ACK-E6. If you're using a Mac, iMovie can create a movie from the folder of stills created in a time lapse sequence. On Windows, try Windows Movie Maker.

Q. I have a Canon 5D and, it seems to me, the recent low-light images I've been making, with exposure times ranging from 1/8 second to 30 seconds or more, show more amplifier bloom and banding than similar images I took when I first got the camera. I don't have any controlled tests to base this opinion on; it's just a gut sense that I am dealing with retouching more of these issues than I used to. (Or, it could be I am just getting pickier as time wears on!) However, this does have me wondering, what should one expect in terms of sensor lifetime? Does the performance (particularly, noise performance) of the full-frame Canon CMOS sensors (and associated electronics) degrade over time? If so, is it a minor, moderate, or major effect? It is unreasonable to expect a FF DSLR to perform roughly the same as new for 5, 10 or even 20 years?

A. To the best of my knowledge, none of the major camera manufacturers has expressed an opinion on the subject, and personally I doubt that they ever would. There are several good reasons why:

  1. Like many other types of electronic devices, the design of image sensors evolves over time. Therefore, what may be true for one particular sensor does not necessarily hold true for every sensor, even if it's the same brand. And for that matter, it doesn't make sense to generalize sensor longevity among different manufacturers.
  2. When it comes to testing longevity, the proof is in the pudding, so to speak. It's possible to test sensors based on actual usage, but it's not possible to simulate the effects of time.
  3. Quite bluntly, in an era where digital cameras are no longer repaired by manufacturers seven years after the end of production, there is no good business reason to claim sensor longevity beyond that point.
  4. For what it's worth, Canon has not detected any deterioration in image sensor performance with any EOS Digital SLR since the company first started manufacturing its own sensors nine years ago with the EOS D30. In other words, the performance in terms of sensitivity and color values has remained stable over that period of time.

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

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 everything, 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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