What is the recommended user maintenance for the external weather seal of Canon "L" lenses?

No lubricants are required to maintain the weather-resistant functions of L-series lenses equipped with rubber seals. In fact, lubricant may harm the equipment if it is transferred to optical surfaces or electrical contacts, and there is also the possibility of damage caused by grit or other foreign matter becoming suspended in the lubricant and rubbing against the surfaces of the camera body and lens during attachment and removal of the lens. So our best suggestion for maintaining weather-resistant EOS equipment is to clean them regularly with a soft, dry clean cloth. Microfiber cloths are excellent for this purpose.

I have an EOS 1D Mark III Camera. I use Sandisk 4GB Extreme III CF memory cards. I recognize that in the camera's high-speed continuous mode, I can shoot 36 images in one burst at ISO 100 in RAW, but at ISO 3200 the number of images per burst reduces to about 12. The same with JPEG "L." At ISO 100 I get 122 photos in one burst, at ISO 3200 only 40. Why is that happening? I recognize that the image size in RAW increases from about 10MB at ISO 100 to about 16MB at ISO 3200, due to noise. But this increase in size per image and the quicker fill up of the internal buffer does not entirely explain the numbers I observe. Do you have a better explanation?

Basically, there are several factors that affect the maximum number of shots in a burst. When comparisons are made with the same memory card, the remaining factors are (in no particular order):

• Buffer memory capacity
• ISO speed
• Exposure accuracy
• Shutter speed
• Picture Style setting (file sizes are smaller in monochrome, so maximum burst increases at those settings)
• Level of detail in the image
• Framing rate (fps)
• Image quality setting (RAW, sRAW, JPEG)
• Compression setting (for JPEGs)
• High speed noise reduction setting in the camera (on, off or auto)

Our ratings for maximum shots in a burst are based on actual product testing in our R&D facilities. Although specific details of our testing methods are confidential, it's safe to say that we use a standardized test target with a fairly high level of detail, and lighting conditions are consistent across the entire picture area. Shutter speeds are fast enough to allow the camera to perform at its maximum framing rate, and exposures are accurate so that the results aren't skewed by lack of detail caused by over- or underexposure.

With the EOS-1D Mark III set to ISO 100, we quote a nominal rating of 30 shots in a burst at 10 fps when the camera is set to RAW mode (see page 53 in EOS-1D Mark III instructions). Many photographers are able to achieve longer bursts with the same camera settings, which can be attributed to varying levels of detail in the image. We also state in the 1D Mark III Instructions (on pages 53 and 54) that "The single image size and the number of shots will vary depending on the subject, memory card brands, ISO speed, Picture Style, etc." The instructions do not quote specific figures for maximum burst at ISOs higher than 100, but we do state (on page 54) that "at high ISO speeds, the maximum burst will greatly decrease." I mention all of this as a foundation to support the contention that in fact users can and should expect a significant decrease in maximum burst with the EOS-1D Mark III at high ISO speeds. Our estimate for the maximum burst is indicated in the camera's viewfinder. The estimate is based on a number of factors including average file sizes as well as image processing considerations and available memory card capacity.

Now, as to why maximum bursts decrease at higher ISO speeds, it's basically an issue of increased processing time per image as well as larger file sizes. The increase in processing time is mainly a function of the noise reduction algorithms we use, which vary according to the ISO speed setting as well as the user-selected high-speed noise reduction setting. Even when high-speed noise reduction is turned "off," varying amounts of noise reduction are still applied to all images, even RAW images.

I'm curious about sensor size (APS-C vs. APS-H) and print size, image quality, etc.

Let's make a couple of assumptions:

- 100 ISO (let's not complicate this with high ISO noise)

- focal length adjusted so both cameras capture the same image

- static subject, same exposure settings, same lens

- ignore the extra "1D Mk III goodies" (like AF & shooting speed) for now.

Since the 1D Mk III and 40D both have 10 meg sensors (3,888 x 2,592 pixels) does that mean that images taken with these cameras should be very similar as far as maximum print size, print quality, etc. are concerned? I'm currently using a 30D but thinking about upgrading to a 1D Mark III in January. I'll be shooting downhill ski racing next March and the extra AF points will be helpful. I used a 30D last winter and it worked fairly well, except when the skiers were doing their "stunts" in mid-air and would suddenly end up missing all the AF points (the smaller skiers were very challenging).

Under the strict limitations you've outlined here, the answer would be yes. I would give you the same answer for images created under the same conditions with the EOS Digital Rebel XTi, which sells for even less than the EOS 40D. So the question now becomes, why do you ask?

This subject came up at a photo meeting a while ago. The general thinking from the "long term" members was that since the APS-C sensor is physically smaller than an APS-H sensor the resulting APS-C images would be grainier when the images are printed at the same size. My line of thought was something like 10 megapixels is 10 megapixels and therefore the resulting prints should be very similar. I've got a feeling that their reasoning may have been a carry-over from the "old days of film" when the physical size of the negative did influence grain and print size. Thanks for giving it some thought and taking the time to reply.

One way to settle the argument is to download *and print* equivalent test photos from each camera. Fortunately, there is a web site that lets you do exactly that, with images that are shot under consistent conditions in a test lab set-up. That site is Imaging Resource. They have comprehensive test reports on most of the popular digital SLRs, including the 1D Mark III, 40D and Rebel XTi.

Here are the URLs for the ISO 100 test images from each camera:

EOS-1D Mark III (ISO 100) USA retail: $4,499 body only

http://www.imaging-resource.com/PRODS/E1DMK3/E1DMK3hSLI0100.HTM

EOS 40D (ISO 100) USA retail: $1,299 body only

http://www.imaging-resource.com/PRODS/E40D/FULLRES/E40DhSLI0100.HTM

EOS 400D/Digital Rebel XTi (ISO 100) USA retail: $799 body only

http://www.imaging-resource.com/PRODS/XTI/FULLRES/XTIhSLI0100.HTM

Just for the heck of it, I'll throw in the PowerShot G7, which is a compact digital camera with 10 megapixel resolution:

PowerShot G7 (ISO 100) USA retail: $499 with lens

http://www.imaging-resource.com/PRODS/G7/G7hSLI0100.HTM

This should prove that image quality at 10 megapixels can be consistently high with Canon digital cameras regardless of the price point. But it's important to realize that ISO 100 produces a "best case scenario" for image quality with most if not all digital cameras available today. Generally speaking, the smaller the pixel, the greater the deterioration in image quality as ISO speeds increase. This is not an absolute rule, because sensor quality and image processing algorithms generally improve when new models are introduced, but digital SLRs as a group generally have a noticeable edge compared to compact digital cameras in terms of image quality at ISO 400 and up.

I am planning to purchase a new L telephoto zoom lens, and the EF 70-200 f/4L IS USM is on my mind. However, I am using EOS 3 and EOS 350D together, and planning to upgrade to full frame such as 5D in the future, and I heard from many people that 200mm would not be long enough on a full frame. So I'm also thinking about the EF 100-400 f/4.5-5.6L IS USM. My primary goal for this lens is nature and landscape photography (I own a 17-40 f/4L, I'm already sick of wide-angle lenses!) Now I am pretty sure to get the 100-400 instead of 70-200; but I'm curious on one thing. The 100-400L IS was produced in September 1998 (almost 10 years ago!). On the other hand, the 70-200 f/4L IS was produced in the end of last year. Would that affect image quality and sharpness, etc. that much? The image stabilizer of the 70-200 obviously features the latest technology and probably is the best one Canon has.

There's no question that the EF70-200/4L IS USM has the edge over the EF100-400/4.5-5.6L IS USM in terms of size, weight, optical performance and image stabilizer technology. On the other hand, the EF100-400/4.5-5.6L IS USM is sharp enough to satisfy even picky photographers, and it is more versatile out in the field than the EF70-200/4L IS USM when it comes to zooming in on small or distant subjects. I am certain you could produce excellent images with either one, but you're the only person who can decide which of these lenses is better for your needs.

Thanks for reading Tech Tips! That's it for now. See you in 2008!

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.)