Can you provide any info on write speeds for the EOS-1D Mark III with Compact Flash cards? I am using Sandisk Extreme IIIs now (have used previous generations for years and never had one problem). I am wondering what speeds the Mark III can write at to determine whether the Sandisk Extreme IIIs are sufficient or whether I should go for the Extreme IVs.

It's tough to provide definitive information at this stage. On one hand, Canon Inc. does not publish specifications for card writing speeds. On the other hand, mass production samples of the EOS-1D Mark III have just started to hit the market, so up to now, independent reviewers like Rob Galbraith have been forced to rely on tests conducted with pre-production samples of the camera that may not be 100 percent the same as mass-production pieces in terms of performance. Nevertheless, the results of Rob's testing with a pre-production sample of the 1D Mark III are promising. Here's what he said in a recent Web article:

"The EOS-1D Mark III has about all the options one could imagine for storing pictures on memory cards, and it does so faster than any previous Canon digital SLR too. CompactFlash write speed is approaching 11MB/second with the fastest cards in our testing, and well over 14MB/second with SD. The camera doesn't support UDMA, so it doesn't take full advantage of the speed possible from cards like SanDisk's Extreme IV and Lexar's 300X. Nevertheless, it is the fastest writing Canon (or Nikon) digital SLR we've tested."

I would suggest that you keep checking Rob's CF/SD Performance Database for updates once he gets a chance to measure the performance of an EOS-1D Mark III mass-production sample camera.

http://www.robgalbraith.com...

A question about dust on the sensor. I'm fastidious about keeping the interior of my 1D Mk2 cameras as clean and dust-free as humanly possible. I regularly - and carefully - clean the sensor using a squeeze-type air bulb. I probably do 90 percent of my shooting at wide-open aperture (f/2.8 or f/4) and never see dust spots on the image. But on the occasions when I go to f/16, f/22 or farther, dust shows up markedly, in places I thought I cleaned well. Can you explain this? I guess a trip up the N.J. Turnpike to Jamesburg is in my plans this week! Thanks for your input.

Due to the design of EOS Digital SLRs as well as digital SLRs from most other manufacturers, dust particles usually end up on a low-pass filter that's positioned a couple of millimeters in front of the actual image sensor surface. When pictures are taken at fairly large apertures like f/2.8 or f/4, the depth of focus at the camera's focal plane is so shallow that the dust particles don't show up in recorded images. However, just like depth of field at the subject plane, depth of focus at the focal plane expands progressively as the lens is stopped down. As a result, dust particles on the low-pass filter begin to show up in images that are recorded at smaller apertures like f/16 or f/22. They're usually not in sharp focus, but the smaller the aperture, the more distinct they become. Getting rid of dust spots in digital images can be a tedious process, but that's a story for another day.

I have an EOS 20D, and when the ISO is jacked up higher than 100, a white, almost glowing speck appears in the same spot on the image. Also, I guess it's important to tell you that you can only see the spot when the image is expanded or you zoom in on its location. Again, this only happens when the ISO is above 100. Please get back to me and tell me what you think.

Based on your description, it sounds like your EOS 20D has developed what's called a "hot pixel." In other words, one of the photodiodes on the image sensor has become defective and as a result, shows up as a bright spot in your images. Like you said, it becomes more noticeable at higher magnifications and higher ISO speed settings. This is a fairly common occurrence, and nothing to worry about, but it can be annoying. If you send your camera to one of our Factory Service Centers, they can repair any hot pixels on your sensor, using a procedure called "pixel mapping." If you want to take advantage of this service, I would suggest calling ahead to determine costs and turnaround time. Here is the contact information for Canon Factory Service in the USA:

Canon Factory Service
Jamesburg, N.J.
(732) 521-7007

Canon Factory Service
Irvine, Calif.
(949) 753-4000

I heard that intermediate ISO setting gives lower image quality than full ISO setting. An example for Canon 5D, ISO 640 would result in higher noise than ISO 800 in a similar lighting and correct exposure conditions, even though ISO 640 requires more exposure. Is this true? If so, why?

I've seen discussions of this topic on various Web sites, complete with graphs and charts that claim to prove the theory that images taken at intermediate ISO settings with various EOS Digital SLRs have more noise and/or less dynamic range than images taken with the same cameras at full-step ISO speed settings. However, to the best of my knowledge, none of these Web discussions have provided actual pictorial images that prove the claims. In my experience, there is no perceptible loss of quality in actual images shot with the EOS 5D or any other EOS DSLR that provides intermediate ISO speed settings. Canon's official statement on this subject is simply that the image quality of all EOS Digital SLRs conforms with Canon's internal quality standards at all available ISO speed settings. In the case of the EOS 5D in particular, image quality is exceptionally high at ISO 3200, and even higher at lower ISO speed settings.

My 420EX flash sometimes fails to fire as many as 10 times in a row on my 1D Mark II body, despite the ready lamp on the flash being lit, and the ready indicator showing in the viewfinder. I have tried to tighten any loose connections, but there don't really seem to be any. The screws in the hot shoe are tight and there is no noticeable play between the flash and the camera. The flash may then go hundreds or even thousands of shots without failing to fire once. No clear patterns seem to have emerged, although I have found that the problem sometimes comes during / after shooting with the flash in AI SERVO (as opposed to one-shot) focus mode. Do you have any thoughts on whether the problem lies in the flash or the camera and what the solution might be?

Because of its limitations (auto exposure only, no support for external power supplies), the recycling speed of Speedlite 420EX depends greatly on the condition of the batteries you're using and the level of flash power that the camera's metering system is calling for. If you want to fire the flash continuously during an 8 fps motor drive sequence with your EOS-1D Mark II, it is entirely possible that the 420EX will not fire until the batteries have had enough time to recycle the flash sufficiently. You can maximize performance by using non-rechargeable lithium AA batteries, shooting at relatively high ISO speed settings, using relatively large apertures, and keeping fairly close to the subject. However, in order to achieve significantly better performance, you'll need to upgrade to a more powerful flash unit that can accept an external power supply, such as Speedlite 580EX II. No matter what kind of Canon Speedlite you use, please observe the warning printed on the first page of the instruction book to prevent degradation of the flash head due to overheating.

I own two 550EXs that I want to use in a master-slave wireless configuration. I need the flashes to fire in manual mode, that is, the same amount of output power each frame according to settings I program. I'm avoiding E-TTL flash for maximum control and repeatability. I hope you can shed some light (no pun intended!) on how the master's ratio settings function when both the master and slave flashes are set to manual ("M") mode. The 550EX allows me to set an "A group" ratio and a "B group" ratio, separately from one another. What exactly is this ratio referring to, i.e., the ratio of *what* to *what*? I tried influencing the flash output of the slave unit by playing with the master's ratio settings to no avail. I am using a Sekonic L-358 flash meter to measure the flash output. A fair amount has been written about wireless E-TTL flash, but I have found nothing on the subject of wireless manual flash. The 550EX user manual is silent on the subject. I am sure you are inundated with questions from Canon users, but I hope you can find time to answer this particular question of mine.

My copy of the instructions for Speedlite 550EX outlines the procedure for "Wireless Manual Flash with Varied Output," starting on page 72. You'll need to read the whole chapter for complete details, but the gist of it is that you set the master unit to Manual flash mode (M), and then use the ratio settings to control the output of the master unit and the remote flashes. As I mentioned in last month's column, the master unit is considered part of Group A when it is set to fire during the exposure. Assuming you want the master unit to fire during the exposure, you have the option of choosing Group A, B or C for the remote flashes. If you select Group A for the remote flashes, they will fire at the same power setting as the master unit. If you select Group B or Group C for the remote flashes, you can control their power settings from the master unit. In a wireless manual flash set-up such as I've described here, the A:B ratio refers to the difference in power settings between the master unit and any remote flashes set up in Group B. Typically, Group A and B flashes are used for frontal illumination of the subject, whereas Group C is intended to illuminate the background area behind the subject. Hope this helps!

I am having a Canon EOS 5D converted to an IR-only camera. If I wanted to use a Canon flash with this camera, does Canon make any kind of filtered hood to attach over a flash? Any third-party vendors with a solution?

Canon does not currently offer any filter holders for its shoe mount flash units, but you can cut and mount gel filters inside a third-party attachment such as the Sto-Fen OmniBounce. However, keep in mind that you really don't need any special filters on the flash for photography with a 5D converted to IR-only. The biggest issue you're likely to face is exposure control. E-TTL may be problematic, because with a converted 5D, the flash metering sensor isn't seeing the same thing as the image sensor. Experimentation is advisable, and in my opinion you'll probably be better off to set the flash to its manual exposure mode for greater consistency.

I have a question about my Canon EOS 30D. Can the Print Button be reprogrammed? I've seen references to changing button function outside the Custom Settings, but there seems to be nothing about the Print Button.

On the EOS 30D, the Print/Share button has two functions: Direct printing and direct downloading to compatible personal computers or storage devices. No other options are available, but both of these functions come in handy for various applications. The direct print function, for example, is extremely useful for event imaging, such as photos taken at youth sports events, at amusement parks, on cruise ships, etc. It's also useful for ID photos, insurance claim adjustments, medical applications, and more. The direct download function is simple to use and effective for many photographers who want a speedy workflow.

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

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.)