Tech Tips
September 2009

by Chuck Westfall

Q: I'm interested in a technical explanation of one particular feature of constant aperture zoom lenses, e.g., EF 70-200/2.8L. Knowing that the aperture is a result of dividing the focal length with the physical diameter of the lenses, we calculate that the required lens diameter for 200mm/2.8 is approximately 70mm. OK. Now, let's assume that we zoom back to 70mm focal length. The physical diameter of the lenses is still 70mm. Why can't we have a lens that would now have f/1.0 (70/70)? In this manner, we would have a 70-200/f1.0-2.8 lens. Pro photographers prefer constant aperture for practical reasons, but is there a technical obstacle in producing such a lens? I'm sure there is, but I'm also sure there would be enough people who would appreciate such a lens.

A: For a simple lens, the definition of f/stop is focal length divided by the diameter of the front element. But SLR zoom lenses are far from simple, and there are many different types, such as wide-to-wide, wide-to-telephoto, and telephoto-to-telephoto. In all of these lenses, it's the apparent size of the aperture, i.e., the "virtual aperture" that counts, not the size of the physical aperture. In the case of a traditional telephoto zoom lens like the EF70-200/2.8L, you can see the virtual aperture change if you look through the front of the lens while you're zooming it. It increases in diameter as you zoom towards 200mm, and decreases as you zoom towards 70mm. But the size of the virtual aperture is directly proportional to the focal length setting, resulting in an effective aperture that's constant at all focal lengths. So an EF70-200/2.8L should really be thought of as a 70mm f/2.8 lens with a sort of "zoom teleconverter" in front of its iris diaphragm.

Wide-to-wide lenses like the EF16-35mm f/2.8L II are essentially inverted telephoto zooms, so they function basically the same as the EF70-200/2.8L except that the "zoom teleconverter" is behind the iris diaphragm. Wide-to-tele zoom lenses like the EF24-70mm f/2.8L achieve their constant aperture differently than either the wide-to-wide or tele-to-tele designs; in this case the iris diaphragm is "cammed" so that it changes its size as the lens is zoomed. You can see this if you look through the lens off the camera while you're zooming it. If the diaphragm was not cammed, the 24-70/2.8L would be revealed as a variable-aperture zoom with a maximum aperture larger than f/2.8 at all focal lengths under 70mm.

Q: Can you comment on "hyperfocal focusing" on digital zoom lens in general? I think there's just too much hype and myth on this subject. To me, it is not practical at all if I have to refer to a calculation/chart on location. Besides, I like shooting landscapes where I place some foreground subjects as close as possible and so having a tack sharp foreground becomes even more critical to me.

A: Setting a lens to its hyperfocal distance produces depth of field that extends from half the hyperfocal distance to infinity. This represents the greatest possible depth of field for any given combination of focal length and aperture value. Hyperfocal focusing is a popular technique when using wide-angle lenses. For instance, with a 24mm lens at f/11 on a full-frame digital SLR like the EOS 5D Mark II or the Nikon D3x, the hyperfocal distance is approximately 7 feet, based on a minimum blur circle diameter (aka, "circle of confusion") of 0.025 mm, which is a conservative value based on an 8x12-inch uncropped print at a viewing distance of 10 inches. Assuming the image format, focal length, aperture, print size and viewing distance listed above, depth of field extends from approximately 3.5 feet (half of 7 feet) to infinity. If any of the variables change, the depth of field will change, strictly speaking. Regardless of changes to the variables, sharpness in the resulting image will steadily degrade both in front of and behind the actual focusing distance, so you may find that you're better off shifting the focus closer to the camera to improve sharpness on foreground objects. Also, be careful about stopping down too far, since optical diffraction may reduce the overall sharpness of the image.

Q: I've seen a few Web sites saying the new EOS 5D Mark II produces a much better printed image as compared to, say, my EOS 5D. Trying to be a good steward of my money, I couldn't really see the need to go from the 5D to the 5D Mark II other than greater pixel count, slightly faster FPS and marginally better low-light capture. I do not really have a need for the video ability, albeit that it is really fascinating what this camera can do! So bottom line, if I make an 18.2-inch print at 240 dpi using the 5D and another at 308 DPI using the MkII, will I really see a difference on paper due to this pixel count, or are they also talking about image quality aside from pixel count? Thank you so much!

A: If all other conditions including digital sharpening are equal, the answer will depend on the sharpness of the lens, the accuracy of the focusing, the elimination of motion blur, and the level of detail in the subject. The sharper the lens and the finer the detail in the subject, the more likely it is that you'll see a difference in favor of the EOS 5D Mark II, assuming the lens is focused accurately and motion blur isn't a factor. The 5D Mark II print will also show less noise than the print from the 5D, especially at higher ISO speeds. To get a feel for this, try printing some sample images shot under identical conditions with both cameras. The "Comparometer" at the Imaging Resource Web site is a good source for samples of this type:

Q: There are many 5DII sample videos on the Web and some are quite good. I would like to see more details on post-production techniques using software like Nero, Adobe, etc. This should include sound recording and editing. Still + video edits would be of interest. Where can you point me for such?

A: Professional-level HD video and audio editing is a rapidly evolving area of interest for many EOS 5D Mark II owners. Most of the online and recorded tutorials I've seen so far are centered on the use of Apple's Final Cut Pro software for Macintosh computers. Here are some examples of that kind of training:

I haven't seen anything comparable yet in terms of canned tutorials for 5D Mark II audio/video editing on the Windows platform, but one of the more interesting developments to emerge over the past several months is the availability of Neo Scene software for Windows and Mac by Cineform:

This application converts native movie files from the EOS 5D Mark II into Cineform .MOV files that are easier to edit with Windows video editing applications such as Adobe Premiere Pro and Sony Vegas Pro. Here are some links to DVD-based tutorials for these applications:

In addition to recorded content, there are also various live seminars on 5D Mark II audio/video editing from a variety of sources. Enter "5D Mark II Seminars" into the search engine of your choice to see some of those offerings.

Q: I am trying to shoot tethered with an older PC laptop, using EOS Utility. I only have USB 1.1, so I don't want to be downloading RAW files every shot, but I want the RAW files for post-processing later. The Canon European Web site says, "Capturing RAW+JPEG gives you much more flexibility. You can download the JPEG files to your computer, while the RAW files stay on the CompactFlash card." However, I cannot figure out how to do this. I can't find any settings or preferences that allow me to select which type of images download from the camera in real time, and which ones don't. Is this really possible, or is the Canon Web site in error?

A: It's definitely possible to set up your camera to transmit only JPEG in real time when the camera is set for RAW + JPEG recording if you are using a Canon Wireless File Transmitter and EOS Utility software, but not for tethered shooting through the USB interface. The details vary somewhat depending on the camera model you're using, but here's the basic procedure for the 5D Mark II and 50D with their respective WFT units:

  1. With the WFT unit mounted to the camera, go to Setup Menu 1 on the back of the camera. (The tab at the top of the screen looks like a wrench with one dot to the right.)
  2. Scroll down to "WFT settings" and press the Set button. This will display the "WFT settings" submenu.
  3. Scroll down to "Communication mode" and select "FTP." (This won't work in PTP or HTTP modes. Also, you'll need to go through another procedure to establish a communication link between your computer and the WFT unit, but that's a separate issue that I won't cover here.)
  4. Once FTP has been set up, go back to the "WFT settings" submenu, select "Set up" and press the Set button. This will display the "Set up" submenu.
  5. Scroll down to "Transfer type/size" and press the Set button. This will display the "Transfer type/size" submenu.
  6. Scroll down to "RAW+JPEG transfer," select "JPEG only," and press the Set button.
  7. Press the shutter button halfway to extinguish the LCD menu, and you should be all set.

Q: I love the sample photos of the new PowerShot G11 compact camera but STILL there is no 3:2 format. I really cannot understand this and I want to ask if there is a chance people at Canon realize their "blindness" and release a firmware with 3:2 option? Do you think this would be possible in the future? What is the technical background for the Canon policy?

A: As a point of interest, the PowerShot G11, like the G10, G9 and G7 cameras before it, is equipped with an optional 3:2 masking option for its LCD display. This feature is designed as a compositional aid for photographers who prefer the 3:2 aspect ratio over the camera's native 4:3 aspect ratio. The image files are still written in a 4:3 format, but it's a relatively simple matter to apply a 3:2 crop for printing or other forms of post-processing. 4:3 has been the dominant aspect ratio for compact digital cameras since the beginning of the market in the early 1990s with models like the Apple QuickTake 100, which had a 640 x 480 CCD sensor based on the technology in use at the time for standard definition video camcorders. As HD video begins to overtake SD in the market, it wouldn't surprise me to see future compact digital cameras changing their aspect ratios to keep up with the times, but they might skip 3:2 and go all the way to 16:9. This is my own personal observation, so please don't construe it as a comment on Canon's future plans or products.

Q: Canon shutters have been rated since the 30D with an "expected lifetime" of exposures. What is the basis for these ratings and now higher use ratings? Is Hardware, Software, and oil used really that different? What is expected life range for products before 30D (10D, 20D, 5D, etc.)?

A: Canon's durability ratings (they have never used the term 'expected lifetime') for focal plane shutters used in EOS cameras are based on exhaustive product testing in the company's R&D laboratories. The details of the testing procedures are confidential, but having worked at the R&D center in Tokyo, I can personally attest to the fact that Canon's testing procedures for shutter durability are quite stringent. Durability ratings are not published for every EOS model, but here is a listing of published ratings that I am aware of:

  • EOS-1Ds/EOS-1D Mark III: 300,000 exposures
  • EOS-1Ds/EOS-1D Mark II, Mark II N: 200,000 exposures
  • EOS-1Ds/EOS-1D, EOS-1V, EOS 5D Mark II: 150,000 exposures
  • EOS 5D, 50D, 40D, 30D, EOS 3: 100,000 exposures

All of these cameras use electronically controlled multi-bladed focal plane shutters, and several design improvements over the years have contributed to improved shutter longevity. For details about the shutter designs of specific EOS Digital models, I would suggest that you refer to Canon's White Paper documents, which are posted at the Canon Digital Learning Center here:

Q: Has anyone figured out why Canon named the EOS 7D as they did? I thought they had a theme going with the 1000D, then the 450D/500D, then the 40D/50D and then 5D and lastly the pro level 1D series? I'm not sure I understand why they named it 7D (and didn't Minolta once had a camera called 7D and then some other brand too?). Why not 60D?

A: There actually is some sense of continuity in the naming of the 7D if you look at the 22-year history of the EOS system. However, the reasoning might not be obvious at first glance.

In the film era, the basic idea for EOS model numbers was clear enough: the lower the number, the higher the ranking. The EOS-1 series ranked higher than the EOS 3, which in turn ranked higher than the EOS 5 (or A2E in North America), which in turn ranked higher than the EOS 7 series, etc.

In the digital era, after some initial models were named for their sensor resolution (as in D30 for 3 megapixel and D60 for 6 megapixel), Canon changed the model numbering scheme for consumer-grade digital SLRs to a chronological base, as seen in the xxD series, the xxxD series and the xxxxD series, with an initial model in each. For example, 10D through 50D are chronological, 300D through 500D are chronological, and 1000D is most likely the first of a series of entry-level models slotted a bit lower than the xxxD series.

But above the xxD series, EOS model numbers appear to honor the original film-based sequence where lower numbers signify higher rank. In this context, the 1D series ranks higher than the 5D series for obvious reasons, while the 5D series ranks above the 7D because of its use of full-frame sensors. It remains to be seen whether this numbering scheme (or feature differentiations) will continue in future models, but it wouldn't surprise me if it did.

Why wasn’t the new camera named 60D? Because the 7D is considered to be the start of a new series in the EOS line-up. It ranks higher than xxD models like the 50D, just as the 50D ranks higher than the 500D even though both have APS-C sensors with the same resolution.

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

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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