I was curious about the advantage, if any, of UDMA compact flash cards (such as the SanDisk Extreme IV series) versus slower non-UDMA cards on Canon cameras other than the 1Ds Mark III, the only Canon camera to support UDMA. I've been debating buying UDMA CF cards but don't know if it will actually be faster on my 40D & 350D.

Because current EOS models other than the 1Ds Mark III do not take advantage of the special features of UDMA memory cards, the biggest advantage when using such cards with these models occurs when using a UDMA-compliant card reader to transfer captured images to your personal computer. In the case of SanDisk Extreme IV cards, the SanDisk Extreme FireWire reader is probably the best choice, but you should check with SanDisk for details.

Is it possible to connect two Canon digital cameras to one Mac computer for tethered shooting?

Even though it's possible to connect two EOS Digital SLRs to one Mac computer via USB, Canon's EOS Utility software can only "see" one camera at a time for tethered shooting. I haven't seen any Mac-compatible software that can handle two cameras simultaneously for tethered shooting, but there is a solution for Windows Vista and XP computers from Breeze Systems, an independent software developer. It's called "DSLR Remote Pro Multi-Camera," and here is a link to some information on it:

http://www.breezesys.com/MultiCamera/index.htm

I would expect that this software could be used on a current Mac running Windows in either Boot Camp or Parallels, though I haven't personally tested it. DSLR Remote Pro Multi-Camera can be downloaded at no charge in a trial version, so you could try it risk-free to see if it meets your needs.

Another way of connecting multiple EOS Digital SLRs to one computer (Mac or PC) is via Canon's optional Wireless File Transmitters. Current models like the 1Ds Mark III, 1D Mark III and 40D support Remote Live View mode, which is more advanced and flexible than EOS Utility for tethered shooting. The computer can still see only one camera at a time in this configuration, but it is possible to support up to nine cameras transmitting to the same computer.

I've been having problems with the 1Ds Mark III crashing in Mac OS X 10.4.11. I've spent lots of time on the phone with tech support with no luck. I even tried updating to Leopard; still no luck. I've had this camera since the first week in December and it has given me nothing but problems on the Mac (on PC it works just fine). Do you have any suggestions?

Please review the following service notice concerning the use of Macintosh version of EOS Utility 2.2 software for tethered operation with the EOS-1Ds Mark III, EOS-1D Mark III, and EOS 40D.

http://www.usa.canon.com/consumer/controlle...

In short, Canon identified a bug with the Macintosh Version of EOS Utility 2.2 software that causes a program crash when releasing the shutter button on the camera during tethered operation with any of the cameras listed above. The solution to this problem is to replace EOS Utility 2.2 with EOS Utility 2.3. Please refer to the Web page for more details and a link to the new software. This information was just posted the day before you sent your message, so it's likely that our tech support teams were not aware of it before then. Hope this helps! Please let me know your results after you've installed the new software.

UPDATE: I received the following note from the same reader: Thanks for the information, I tested the new software last week and it worked just fine. I went on a big job this week at a 10 million dollar-plus house in Fort Lauderdale and it performed outstandingly, just like my 1Ds Mark II used to. Again I'm glad they finally got a fix for it.

Is there a formula for calculating the angle of view for a lens mounted on an APS-C digital SLR? Most lens charts only seem to show angle of view for the full-frame 24 x 36 mm format. This question has come up in class a few times and I am at a loss to figure out the math.

A reasonably accurate way of calculating the angle of view for a camera equipped with an APS-C sensor compared to a camera equipped with a 24mm x 36mm sensor is to use the ratio of the diagonal lengths of each format. This is somewhat complicated by the fact that not all APS-C sensors are exactly the same in terms of image area: for instance, Canon's APS-C sensors have ranged from 15.1mm x 22.7mm for early models like the D30 and D60 to 14.8mm x 22.2mm for recent models like the Rebel XTi and XSi. APS-C cameras from other manufacturers have sensor sizes that are a bit larger than that, at approximately 15.8mm x 23.6mm or thereabouts, so if you want to be as accurate as possible you need to know the actual dimensions of the sensor for your particular camera model.

But for the sake of explanation, let's just pick a measurement like 14.8mm x 22.2mm and be done with it. In that case, the diagonal of the format is approximately 26.7mm. The diagonal of the 24mm x 36mm format is approximately 43.3mm, so the ratio of this particular APS-C variant to full-frame is approximately 0.617x, i.e., 26.7 divided by 43.3. With that information, we can take the diagonal angle of view for the 24mm x 36mm format and multiply by 0.617 to get the diagonal angle of view for APS-C. Taking a 50mm focal length as an example, the diagonal angle of view for the 24mm x 36mm format is approximately 46 degrees, so the diagonal angle of view for the same focal length on the APS-C format is approximately 28.4 degrees.

I have several technical questions as follows:

Focus points – I find that my style of shooting requires me to focus and recompose because the focus points on most cameras are generally centered, and my main subject is quite off-center. I hear that sports shooters also have this problem. Even the EOS 3 with its 45 points covering mostly the center of the frame I had to recompose and now with the EOS 40D I find the same problem. Are there any technical reasons for the focus points being centered, or is it a design choice? It would be much better to have focus points available in the extreme corners, almost like an outer ring of focus points for these specific situations. Is this technically possible?

Lens aperture for focusing operation – It's a given that most consumer cameras (Minolta/Sony excepted) can focus down to f/5.6 and pro cameras can do so down to f/8. This has been mostly true for the last 20 years of AF photography. Is it not now possible with these high ISO digital cameras to improve on that and have AF working at f/8 on all cameras, or even f11? Surely phase-detect focusing must have advanced along with the other camera functions? Is it perhaps a marketing issue or are there physical impediments to extending AF performance with small aperture lenses? One last item - is it possible to integrate phase and contrast detection to have the besot of both systems working to achieve a faster and better focused image, or operate when light levels are low (i.e., use the best focusing system when the conditions require it)?

ECF Focus – Eye Controlled Focus is a Canon exclusive function. I had it on the EOS 3 and mostly it worked well and helped avoid some of the focus-and-recompose situations. However, after the EOS Elan 7NE it has not been offered anymore, and certainly not in any digital camera. Is this simply a marketing issue? The fact that ECF was in a consumer film camera (costing not more than $400) makes me think that this feature isn't particularly expensive so could be added without significantly altering the cost structure of newer DSLRs?

Thanking you in advance for your replies.

1. There are several technical reasons why it's difficult to position focusing points near the edge of the frame on a 24mm x 36mm format camera. It's basically a "Catch-22" situation:

a) The phase-detection AF method that's been in use on most analog and digital SLRs since 1985 relies on a detection module positioned in the base of the camera's mirror chamber. Incoming light passes through the main reflex mirror to an auxiliary or sub-mirror, which reflects it down to the AF detection module. It is physically impossible to increase the width or height of the sub-mirror beyond the limits of today's technology without losing the light from the edges. However, within the limits of focus point positioning, phase detection AF is fast and accurate, and high-quality predictive AF (i.e., focus tracking) is possible.

b) The contrast-detection AF method that's been in use on most compact digital cameras reads its data directly from the image sensor. The nature of this system permits focusing points to be positioned virtually anywhere in the picture area, but the drawback is that the contrast detection method is slow and not responsive enough for fast moving subjects. Another complicating issue is that focus tracking between shots during continuous shooting is virtually impossible. New digital SLR cameras like the EOS Rebel XSi provide both phase detection AF and contrast detection AF (in Live View mode) for the ultimate in flexibility, but each AF system has clear limitations as outlined above.

2. The f/5.6 limitation for maximum aperture in phase-detection AF has virtually nothing to do with the level of light presented to the system. Instead, it's a matter of the diameter of the beam of light that's projected towards the AF detection module versus the width of the AF sensor arrays. Therefore, I doubt that there's going to be any significant change in the specifications for maximum aperture range as long as SLR cameras continue to use phase detection AF.

3. I have stated numerous times on the Web and at least twice in Tech Tips that it is obvious by now that the omission of ECF in EOS Digital SLRs is a marketing decision, not a technical issue. We get user requests for ECF from time to time, but to be blunt, customer demand so far has been insufficient to justify adding this feature. I'll never say never, but don't hold your breath on this one.

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

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