Type	Digital SLR
	Shutter Range	1/8000 to 30 seconds
	Shutter Type	Vertical Travel, Electronically Timed Focal Plane
	Meter Type	CMOS
	Meter Range	EV1 - EV20
	Exposure System	35 zone TTL
	Lens Mount	Canon EF Autofocus
	Battery	BP-511

• Portrait (Low Aperture, center spot metering)
• Landscape (High Aperture, averaging metering)
• Close up
• Sports (high shutter speed)
• Night scenes (Auto flash, combined with slow shutter speed)
• Flash off

• Manual exposure
• Aperture Priority
• Shutter Priority
• Automatic Depth of Field

The Effect of Film Speed on Image Quality of the 20D
	A tightly cropped photo of my desk at home in normal room light.  ASA 400 is to the far left, and ASA 1600 is to the right. For comparison sake a shot at ASA 100 is just to the left. Though there seems little difference between 100 and 400, the difference between 400 and 1600 is distinct. I usually shoot at 400.
The imager of the 20D is capable of operating at film speeds ranging from ASA 100 to ASA3200. The higher film speeds bring with them the traditional disadvantages well known to generations of film photographers. Chief among these are noise, and reduction of gray scale. In film cameras, this is produced by the need for larger, more irregular grains of silver halide, needed to work with smaller amounts of light. This tends to make the pictures grainier.         On digital cameras, noise is an artifact of the natural, random signals given off by the sensor. These signals are generally below the threshold of the signals produced by the light striking the face of the sensor, and are overpowered by them. As the light intensity drops, these lower level signals become noticeable. Another problem of operating at low light levels, using fast speeds, is the problem of loss of contrast, and color saturation. still, a higher ASA rating will get you a picture that might not be possible with a lower setting.         The photo to the right shows the 20D in clean mode, with its mirror up to allow access to the imager. The imager itself is the small blue/green square visible at the rear of the mirror box. The mirror itself is that slab of glass seen flipped up on the roof of the mirror box. Also visible are the EOS electrical contacts, towards the bottom of the lens mount.

The Effect of Image Quality Settings on the Canon 20D
High Quality	Enlarged sections of photos taken of the same subject, with the same exposure, under the same conditions. Only the quality level is changed. I always shoot at high. Memory is cheap.	Average Quality
In addition to the film speed setting, the 20D offers the option of three resolutions, and two quality levels. The purpose of different levels of resolution is intuitively obvious. The selection of quality levels is not really an artistic or an adaptive control. The main function of the selection of quality levels is to give the photographer some control over the file size of the images produced. This is done by selecting between different levels of compression when the images are being stored. In the 20D, images are generally stored in the JPEG format, which is a compressed format. Compressed formats use algorithms to look for patterns so that they can throw details away, and give smaller file sizes. These same algorithms are used when the image is viewed, to reconstruct the details that were taken out. Naturally, nothing conforms exactly to any pattern or algorithm, and bits of the detail will not be reconstructed. At higher compression levels, you get smaller files, but less accurate reconstruction all the fine details. The more irregular, textured, or busy a scene is, the more the compression effect will be noticed. The best candidates for high compression are sunsets, and wide open vistas. The worst subjects for high compression are diagrams, printed pages, or anything with a considerable amount of detail or contrast.

    The meter will set exposure down to EV 1, at a rated sensitivity of ASA 100. With an f 1.4 lens, this is a 1 second exposure. With the standard F 3.5 lens that comes with most kits, this would be an 8 second exposure. The meter breaks the image up into 35 different zones of measurement. This gives the capability of setting up a number of different metering patterns for different  types of situations. This is what makes the Easy Shooting Zone settings possible. So for landscapes, the metering pattern will be bottom weighted, under the assumption that the upper portions of the frame will be filled by the relatively bright sky. For portraits, semi spot metering will guarantee that a face which fills the center of the composition, as is the case in most portraits, will be perfectly exposed. For Close ups, center weighted is just the thing. My favorite feature is a resurrection, of sorts, of the old TTL semi spot metering of the old F series. When this option is chosen, the EOS series does the old FD cameras one better by using a 9% circle, as opposed to the FD 12% rectangle. This is the only metering setting that I use.
    The photographer has two ways to view his work. The first, and most obvious, is through the viewfinder. As a reworked SLR, the 20D has a regular eye level, pentaprism viewfinder for through the lens viewing via a ground glass screen. The eyepiece has a dial to give up to 2 diopters of visual correction, for users who wear glasses. The viewfinder itself displays the nine focusing marks (user selectable, of course), along with shutter, aperture, flash, and autofocus information. There is also a slightly shaded ring, which shows the metering area when semi spot metering is selected. What is missing from the viewfinder, in this autofocus camera, is any kind of focusing aid. This can make precise focus with a non autofocus lens, rather difficult, particularly when using slow lenses.
     The viewfinder is shown in the photo to the right. Visible is the central circle which shows the metered area when using partial metering. The nine focus points show up clearly, and flash red when selected manually, to indicate the chosen focus point. The bottom display shows the camera is set at 1/100 shutter speed, with an aperture of F 10, and is at least two stops underexposed when compared to auto exposure. The green dot far to the left indicates focus lock, and the number nine shows that there is room for at least nine rapid fire shots in the buffer.
    To check photographs already taken, there is a built in color LCD screen on the camera back. The screen can not be used to compose or preview photographs, as it only displays what has already been stored in the memory. The resolution of the 1.8", 118,000 pixel LCD is about half that of a standard VGA monitor, and not too far inferior to that of the sensors on cameras from just a decade ago. There is more to the LCD screen than a fancy way to view your images. The images can be zoomed in on, and the screen can also be used to view camera settings. On top of all of this, Canon has included a way to display histograms, charts of color balance, brightness, contrast etc., on this display. This is not a feature that I use, preferring to view and adjust these levels in Photoshop (if at all), but some users might find them convenient.
    Two dials control most of the operations of the camera. The dial to the left of the pentaprism, selects the shooting mode, while the dial to the right sets the exposure. It is possible to use the camera, while never touching another control, other than the power switch. For those who enjoy a bit more creative control of their image, the 20D is able to oblige. In addition to the easy Shooting Zone Settings, and the  Creative Zone settings, the camera has exposure compensation, and the option of setting parameter definitions, which allow for customizing the color balance, brightness, contrast, and  intensity. Different sets of parameters can be defined as sets, so that the demanding photographer can create a special parameter set for indoor lighting, another for cloudy days, and still another for bright sun.

Personal Observations:
        This camera is very similar to my old D30, and somewhat similar to my Digital Rebel. These are substantial cameras, with metal frames, and sturdy bodies. They have the full range of expected features, auto exposure and focus, a TTL system for flash, various parameters and custom settings, a rear LCD for instant photo viewing, and a built in flash. The 1/8000 top shutter speed is the same as that on Canon's current models, and though higher resolution cameras are available (I have several), the 8.2 MP resolution is more than enough for most situations, and I use this camera often.

        This was the first model capable of taking the new EF-S type lenses. The lenses are similar to the standard EF lenses, except that they have the rear element closer to the film plane. They also focus to a smaller image. They are more suited to the APS-C size sensor, and the image does not need to cover the entire 35mm frame. The biggest advantage of the S series of lenses is that they can be made somewhat smaller, lighter, and less expensive. The disadvantage is that if you were to use such a lens on a standard 35mm camera, the image would vignette, and not cover the full frame.
        The 20D shares the autofocus feature of all of the EOS line, in common with almost every camera made these days. It is very difficult to find a manual focus camera, and most consumers have been brainwashed into believing this is a must have feature. I have gotten used to autofocus; but never learned to like it. Most photographers can do the job faster, and there are some situations, notably low light, under which autofocus does not work. There is also a problem, with certain compositions, of getting the camera to focus on the right subject. There are options to set, the 20D has nine different focus points, but the whole thing would really be much easier and faster with manual focus. With autofocus being a standard feature these days, viewfinder focusing aids have become a thing of the past, except for some expensive aftermarket focus screens. The user has little choice but to rely on autofocus, stop down, or settle for pictures which are somewhat unsharp. This is my biggest complaint about the new generation of autofocus SLR cameras.
        The 20D has a built in flash, which pops up from the top of the pentaprism housing when the camera meter decides that it is needed. The unit is fully integrated with the camera meter system, and has an ASA100 rating of 43. This is more convenient than I had first thought, and the flash comes in very handy for snapshot type photography, and even more handy as a fill flash for taking some of the contrast out of brightly lit scenes. For the more demanding or flash dependent photographer, Canon offers a number of very capable flash units which are able to fully integrate themselves with the camera's metering, and focusing systems.

       My best friends on this camera, are the exposure hold button, and the manual override. The exposure hold button is the easiest way to get by the computer automation, or to photograph off center subjects, and still get a proper exposure. It works best when the meter is set for 9% partial metering. There is an exposure compensation system, for backlit, offset, or oddly colored scenes, but I have never had good results with exposure compensation; it takes too long, and requires too much guesswork. After getting used to the system, I can now quickly set the aperture and shutter speed after metering. I can then leave them while the camera finds its focus. This is almost as fast as my old manual match needle camera.

        As with all of the current crop of digital cameras, you can shoot all day (sometimes all week) without changing the memory chip.  Batteries are another matter, and might only last for 1000 or so shots at the most; but batteries are cheap, chargers are small, and spares can be brought. I have never run out of memory without having run down my battery first. In answer to this, Canon offers it's battery grip, which fits seamlessly on the bottom of the camera, a bit like a motor drive, and plugs into the battery compartment of the camera. It holds two standard 2200 mah BP-511- batteries, or six AA batteries of up to 2600 mah.

        With the battery grip, and the 8 GB memory card that I ordinarily use, this camera can take approximately 2000 photos before recharging or using another card. This should be enough for even the most insatiable photographer.