Is there any reason I should consider reducing the quality level of Large JPEGs from 10 on my EOS-1D Mark II? I'm surprised the SI Photo Web site recommends a quality level of 6. My newspaper doesn't want RAW files shot, so a maxed-out JPEG quality setting seems to make sense unless I'm missing something.

Sports Illustrated's recommendation of Level 6 compression for Large JPEGs from the EOS-1D Mark II was most likely based on testing that showed no visible difference in image quality on the printed page for higher JPEG quality settings. As long as that's the case, the benefit of Level 6 over higher JPEG quality settings like the camera's default Level 8 or your preferred maximum quality Level 10 is smaller file sizes, which result in longer bursts at 8.5 fps, more images per memory card and faster per image transmission times. It is true that there are fewer JPEG compression artifacts in Level 10 images compared to lower image quality settings, but it's also true that Level 10 results in significantly larger files on the memory card. This is not a big deal for most shooting situations, but it could become problematic for the burst mode shooting that is quite common in professional sports photography.

What is the "Native" ISO sensitivity of the 40D sensor? By native I mean the ISO setting that does not require any signal amplification or reduction to the sensor data, or at least the minimum setting of either amplification or reduction. I would assume that this native ISO would provide the best Signal/Noise ratio for pictures.

Your logic is sound, but Canon does not publish any specifications for the native sensitivity of its digital camera image sensors. Generally speaking, you'll find that S/N ratios with EOS digital SLRs are at their best in the lower ranges, and any differences in noise levels and dynamic range from ISO 100 to approximately ISO 200 are so minimal that they're not worth worrying about. If this matter truly concerns you, my best advice is to take some sample photos at each ISO speed setting and examine the resulting images to see which setting you prefer.

On a certain online forum there is a long-standing argument about the EOS 5D's auto-focus (and now the EOS 5D Mark II) that comes from the fact that the white papers are a little ambiguous. The problem is that some people claim that the autofocus calculations are performed by a separate processor that is independent of the DIGIC processor.

With EOS Digital SLRs, AF calculations and lens drive commands are typically executed by dedicated CPUs rather than the DIGIC processor itself. However, the overall speed of the AF system and many other camera functions depends on the speed of the DIGIC processor, or dual DIGIC processors in the case of the EOS-1Ds Mark III and EOS-1D Mark III.

I have been looking for some advice concerning back button focusing. I am shooting with a Canon EOS 30D and have 3 "L" series lenses. I primarily shoot my teenage daughter's competitive cheerleading competitions which are usually very poorly lit with the EF70-200mm f/2.8L IS USM zoom lens. What is the difference between Custom Functions 4-1 and 4-3? Do I need to hold the AE Lock [*] button constantly? Is there anything else I need to know? I thank you in advance for any help/guidance.

I wrote the following information for the EOS-1 class cameras, but it applies equally to the EOS 30D: Custom Function 4 allows the photographer to control which button on the camera is used to start or stop AF. It also ties in with AE Lock when the camera is set to an AE mode.

• C.Fn 4-0 (the default setting) starts AF and AE when the shutter button is pressed halfway. AE Locks automatically upon focus completion when the camera is set for the combination of One-Shot AF and Evaluative Metering. With other AF modes or metering patterns, AE Lock can be initiated manually by pressing the AE Lock button on the back of the camera.
• C.Fn 4-1 switches AF start to the AE Lock button, and starts AE Lock in AE modes with any metering pattern when the shutter button is pressed halfway. This mode is popular with sports photographers and some photojournalists, especially those who originally learned photography with manual-focus SLRs. It works particularly well with USM lenses that have distance scales, because such lenses feature full-time manual focusing even when the lens is set for AF. With C.Fn 4-1, the photographer can manually focus such a lens at any time, and then start or stop AF independently from shutter release simply by pressing or lifting the thumb off the AE Lock button.
• C.Fn 4-2 keeps AF start on the shutter button, but allows the photographer to stop AF temporarily by pressing the AE Lock button. AE Lock is unavailable in this mode, but it doesn't make any difference when the camera is set for manual exposure as it often is for professional sports photography.
• C.Fn 4-3 is almost the same as C.Fn 4-1, except that there is no AE Lock. This mode is useful when shooting sports photography in changing light situations, because it updates the exposure automatically in AE modes as the subject moves from shadow areas to sunlit areas or vice versa.

Based on this information, the choice between C.Fn 4-1 and C.Fn 4-3 with the EOS 30D depends on the following conditions:

1. Manual exposure: If you set the camera for manual exposure mode, there's no functional difference between C.Fn 4-1 and C.Fn 4-3. Choose whichever one you like.
   
   
2. Auto exposure:

   (a) In an AE mode like P, Tv or Av, C.Fn 4-1 will lock the exposure in any metering pattern as soon as you touch the shutter button. This is great for One-Shot AF with stationary subjects, because it lets you focus and recompose without losing the meter reading.

   (b) In P, Tv, or Av, C.Fn 4-3 updates the meter reading constantly wherever you aim the camera. For this reason, it's a good fit for sports photography with moving subjects in AI Servo AF.

You definitely don't need to keep AF active all the time, even for sports photography. With either 4-1 or 4-3, the more you practice, the better you'll get at judging when to activate AF with the AE lock button and when to suspend AF by lifting your thumb off the AE lock button. During a typical shooting sequence, you'd want to keep the AF going as long as you've got a clear view of your subject, and you'd want to suspend AF temporarily if an object, for instance another athlete, gets between you and the subject.

Last but not least, if you're stuck with poor lighting as you mentioned, you'll probably be best off to limit yourself to the center focusing point on the 30D. It's the most sensitive one, and it's cross-type which will make it easier to work with low-contrast subject matter.

One other question, which metering mode should I use – center-weighted average, evaluative, or spot? What about exposure modes?

For indoor sports in a gym, I would suggest manual exposure mode with center-weighted average metering. Take a reading off the floor and then take a test shot. Check the histogram to see if you're satisfied with the exposure accuracy. If not, adjust your shutter speed, aperture or ISO and make more test shots until you're happy with the exposure. In your case, I'd set the ISO to 1600 immediately and open the lens to f/2.8. Hopefully, you'll end up with a shutter speed that's at least 1/250 or faster. If not, you might want to consider a newer camera like the EOS 50D for its higher ISO settings, and/or a faster lens like the EF135mm f/2L USM.

AEB with MLU and Timer question: On the original EOS 5D I have my custom setting permanently set to Mirror Lock, AEB, 2 second timer, because I use this setting a lot. It is a complete PITA [pain in the ass] to have to press the shutter three times when you want one bracketed exposure because there's more chance of camera vibration or movement. On the new EOS 5D Mark II is there a facility to set mirror lock with auto bracketing and timer (or remote) where the camera will fire the three shots of AEB from ONE press of the shutter button? If not, why not?

You can get three consecutive AEB frames in one shutter press with the EOS 5D Mark II with mirror lock by setting the camera to Live View mode with continuous advance. For best results, use a remote switch like the RS-80N3 or TC-80N3 to eliminate camera shake. The 5D Mark II fires at 3.9 fps in continuous mode, and the interval between shots is not adjustable. If for some reason you want to shoot at a slower rate, you can fire one frame at a time with the remote switch. There's no need to set a self-timer delay in Live View, because the mirror is already locked up.

I have optional focusing screens for EOS-1Ds Mark III bodies. I am changing them out, and can't keep up with which is which. I have two screens and on the little tab it says: "CIV," where IV appears to be Roman numeral. The 4x5 black crop screen says "CIII." Are these screens marked in any other way to know if they're Ee-A or Ee-S?

EOS-1Ds Mark III focusing screens are "Ec" series, as opposed to EOS 5D focusing screens, which are "Ee" series. It sounds like you have the Ec-C IV, which is the standard screen for the 1Ds Mark III, while your crop screen is a custom modification of the slightly older Ec-C III, which was the standard screen for the EOS-1Ds Mark II. The Ec-C IV is a touch brighter than the Ec-C III, but otherwise they're basically similar. The Ee-A is the standard screen for the original EOS 5D, and other than the body compatibility, it is basically the same as the Ec-C III. If you wanted to try one of the Super Precision Matte screens for manual focusing with large-aperture lenses, here's a list of what you would need according to the camera body in question:

EOS-1 class (any vintage): Ec-S
EOS 5D: Ee-S
EOS 40D/50D: Ef-S
EOS 5D Mark II: Eg-S

Here is my issue: I have owned the EOS-1Ds Mark II and now the EOS-1Ds Mark III. During the 1Ds II period, I bought these EEs and 4x5 screens. I guess I thought they were compatible with the 1Ds III. I have changed them out so much I don't know which is which. The "extra screen" in that plastic case with tweezers has marking on the tab: "CIV." The screen I just pulled out of the 1Ds III is marked the same way: "CIV." Plus now, I have to make sure I have the Custom Function set right, for the appropriate screen. I hope I have not totally messed up here. I'm having focus issues with the EF50/1.2L, so I'm testing everything – both bodies.

The "Ee" screens are not compatible with EOS-1 class cameras, so unless you've got an original 5D, you should sell them or return them for credit. The screen with CIV on the tab is the Ec-C IV, which is intended for use with the 1Ds Mark III and 1D Mark III. If you install this one to your 1Ds Mark III, set C.Fn IV-11 to 0, the default. If you install the Ec-C III (the screen with CIII on the tab) to your EOS-1Ds Mark III, set C.Fn IV-11 to 1.

I appreciate your technical insight into the EOS system. It's certainly helpful! I have a question that's been on my mind for a while. I've often wondered how long my Canon EOS 5D can keep using the same Compact Flash cards. Do CF cards ever wear out? Are professional photographers expected to recycle their CF cards every few years? I'd hate to have my card unexpectedly fail on me during an important event!

According to ePHOTOzine:

Apart from the fact that technology leads us to ever growing capacities and speeds and, therefore, sometimes rendering certain card sizes [i.e., storage capacities] such as 16MB or 32MB obsolete, it is worthwhile to note that memory cards have a limited life expectancy. Again there is a difference; single layer cards may allow in excess of maybe 100,000 read-write actions, whilst multi-layer cards may only allow around 10,000 to 15,000.

Based on this information, I would agree that it is a good idea for professional photographers to replace CF or SD flash memory cards, especially high-capacity versions, at least once every couple of years, depending on the frequency of usage.

Is there a preferred way to pack a camera/lens combo in a camera bag? Is it more desirable to have the lens mounted on the body or to keep them apart? This question revolves around the issue of being able to arrange a given set of lenses and camera body in a camera bag.

It's always safer to pack bodies and lenses separately, especially when multiple cameras and lenses are stored in the same gadget bag. However, keeping a lens mounted to the camera is also OK as long as you're absolutely sure there won't be any strain on the lens mount.

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

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