I have a problem with a Mark III used with a 17-35 f2.8 and a 550EX flash in dark situations. In One-Shot AF sometimes the shutter does not release. If I put the AF in AI SERVO the shutter releases but all the images are out of focus. Are there some incompatibilities between the new camera and the old lens and flash? Can some function make this system work better?

As stated on page 22 in the Instruction book for Speedlite 550EX, the 550EX's AF Assist beam is intended for use with focal lengths of 28mm and longer. You should still be able to use it throughout the entire zoom range of your EF17-35mm f/2.8L lens when manually selecting the camera's center focusing point, but the coverage of the beam may become inadequate for off-center focusing points when using focal lengths shorter than 28mm. Additionally, the usable distance range of the 550EX's AF Assist beam is approximately 10 meters/33 feet at the center, but only 5 meters/16 feet at the edges. Therefore, please be aware that the AF Assist beam may become ineffective with distant subjects, even when using a focal length of 28mm or longer. Last but not least, keep in mind that the AF Assist beam is only active when your EOS camera is set to One-Shot AF mode.

I have a pair of questions concerning point and shoot cameras: If a user decreases the pixel count on a Canon PowerShot G9 from 12MP to 6-8MP does image quality improve at higher ISO settings and in low-light situations? Does decreasing the pixel count essentially create a bigger sensor with fewer pixels, such as is found on a Fujifilm FinePix F30 or F31fd?

There is no significant improvement in noise levels at any ISO setting when shooting in-camera JPEGs at the 8MP "M1" or 5MP "M2" settings with the PowerShot G9, compared to shooting full-resolution 12MP images. However, if you are interested in extracting the maximum image quality the G9 can produce, I would suggest using the camera's RAW mode and applying noise reduction during post-processing in your personal computer. Canon's RAW Image Task software, supplied at no extra charge with the G9, has an Adaptive Noise Control slider that does a good job at reducing noise while retaining a high level of fine detail. The resulting images, especially when printed, tend to be sharper with less noise than those produced by most other point-and-shoot digital cameras regardless of resolution or pixel size at equivalent ISO speed settings.

I am a newspaper photographer, who has been working with EOS 1D series, from Mark I to Mark IIn, and now our paper has issued us Mark III cameras. I am still a bit behind the learning curve regarding the changed controls, but as I am using the IIn alongside the III (and 1Ds for remotes as well), I wanted to be able to reproduce my control setup for the new body as well. What I was hoping for, is there some combination of custom functions in the 1D Mark III to allow for the old way, that is, AF Sel. button working as Aperture button in Manual (where the +/- button is then changed to AF selection)?

The control layout of the EOS-1D Mark III with its current firmware cannot duplicate the control layout of the Mark I and II series cameras exactly. I am happy to relay your request for this capability, but in the meantime, I would suggest that you read the following guide for getting the most out of the Mark III cameras:

http://www.usa.canon.com/dlc/controller...

I have a Canon EF25 Extension Tube. When I bought my EOS 20D I kept on using it not knowing there had been a new version released, the EF25 II. Are there any compatibility issues to be concerned about?

The II-series EF Extension Tubes (EF12 II & EF25 II) are compatible with Canon EF and EF-S lenses, while the original EF Extension Tubes (EF12 and EF25) were compatible with EF lenses exclusively. There are no compatibility issues on the body side, but you'll need a II-series if you want to use a Canon Extension Tube with an EF-S lens.

I am a newspaper staff photographer and have been using Canon equipment since 1973. I recently got the bug to adapt an old manual-focus Tamron 300mm f/2.8 to the Mark II N bodies I now use. I found a mount on eBay to fit the body and lens together, but every attempt to use it gives Err 01 (faulty communication between lens and camera) and no photo. If I can find a menu workaround I am willing to work with manual exposure and manual focus at f2.8 for specialized uses. Is there a workaround on the Mark II N or the original EOS 1D to get the shutter to fire? Are there any Canon digital bodies that will work this way?

There is a mechanical switch in your EOS camera body's lens mount, at roughly the 10 o'clock position when viewed from the front of the camera, that is normally engaged when a fully-coupled Canon EF lens is attached. This switch causes the camera to send an electronic "handshake" request to the lens to determine its status. The camera is programmed to shut down and display an error code unless it receives a proper response from the lens. Your manual focus lens has no electronic contacts, so the camera thinks the lens is defective and therefore refuses to allow the shutter to be released.

The source of the problem is most likely the lens mount converter. The defective part of the converter is its EOS-side bayonet, which should have been modified in such a way that it would not trip the mechanical switch in the camera body's lens mount. One workaround is to partially disengage the lens from the camera body so the switch isn't engaged. But this is not very secure, and it's impractical unless the lens is mounted on a tripod. Another workaround would be to replace the defective converter with one that has a correctly modified lens mount. Canon used to offer FD-EOS Lens Mount Converters that were properly modified. These products were available from the late 1980s until about 2000, but they are no longer being manufactured or sold. You might be able to find one on the used market, or you might be able to find another independent converter that works properly with your EOS camera.

The instruction manual for the EF24-105mm f/4L IS USM says to use the 77mm Circular Polarizer II, which is apparently a thin-rim filter like I use on my EF17-40mm f/4 L USM. Is the thin filter also suggested for the EF24-70mm f/2.8L USM? All lenses are used on the EOS 1Ds Mark II.

The instructions for the EF24-70mm f/2.8L USM lens do not specify a thin-rim circular polarizer, and it is not an absolute requirement even on a full-frame digital SLR like the EOS-1Ds Mark II. However, since you already own a thin-rim circular polarizer for your EF17-40mm f/4L USM lens, you might as well use it on the 24-70mm lens since they both have 77mm filter mounts.

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

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 all inquiries, 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.)