Minolta XG-M SLR


The Minolta XG-M is a 35 mm single-lens reflex camera, or SLR. The SLR is the most versatile type of still camera, and is the type most used by professional photographers. In an SLR, the viewfinder image goes through the main lens, so the photographer can see the same image that will appear on the film. If the main lens is changed to a different focal length, the photographer will automatically see the effect of that change. With an SLR, unlike rangefinder cameras, there is no worry about parallax errors in closeup shots. In order to "share" the main lens with the film, a flip-up reflex mirror is used. The mirror is located behind the main lens and reflects the light from the lens into the viewfinder optics.

The viewfinder optics consists of a focusing screen, a pentaprism, and viewfinder lenses. The focusing screen is used for focusing the image. The focusing screen is located the same distance away from the lens as the film. Thus, when the image is in focus on the focusing screen, it will also be in focus on the film. The image from this screen is reflected up through the pentaprism on top of the camera, back through the viewfinder lenses, and out to the viewfinder. When the camera's shutter is released to take a picture, the reflex mirror flips up, allowing light to go back through the shutter, and then to the film. During this time, the image to the viewfinder is blocked. For short exposures, this appears as a brief wink, but for longer exposures, it's a long blackout. This also means that when taking a flash photograph, the flash cannot be seen through the viewfinder, and the photographer may not be aware of whether or not the flash went off, unless he keeps both eyes open.

In SLR cameras, the shutter is located in front of the film. It is called a focal plane shutter, since it is just in front of  the focal plane of the lens. Non-SLR cameras, like point-and-shoots, usually have the shutter built into the lens.  The focal plane shutter must be as big as the film frame, so it tends to be larger and more complicated than in-lens shutters. To operate at high shutter speeds, the focal plane shutter turns into a moving narrow slit. The faster the shutter speed, the narrower the slit. This has the side effect that can cause rapidly moving round objects to appear oblong at high shutter speeds. Focal plane shutters tend to have very fast shutter speeds compared to in-lens shutters. The XG-M has a maximum shutter speed of 1/1000 of a second.

Because the photographer must view the image through the main lens, its opening , or aperture, must stay wide open while viewing and focusing to provide a bright image. However, the aperture must close to its correct setting when taking the picture. The SLR camera has a mechanism to close the aperture only when the picture is being taken. The depth of focus is affected by the lens opening. To view the depth of focus, the camera has a feature to manually close the aperture to its current setting.

To determine the correct combination of shutter speed and aperture opening to take a properly-exposed picture, SLRs often have exposure control systems. Some cameras are completely manual and rely on the use of an external light meter. Other cameras have built-in light metering and exposure control systems. These require light sensors to measure the amount of light available on the subject. The XG-M uses a through-the-lens system that measures the amount of light that comes in through the lens. Photocells are mounted on the viewfinder's pentaprism and are most sensitive to the light in the center of the viewfinder image. This is called center-weighted.

The XG-M uses a type of automatic exposure system which is known as aperture-priority. The photographer manually sets the aperture according to the desired depth-of-focus, and the camera automatically sets the shutter speed to provide the proper exposure. If the camera picks a shutter speed that is too slow, the lens must be manually opened wider.

One advantage of the SLR is that the lenses can be easily removed and interchanged. It can take a wide range of lenses from extreme wide angle to extreme telephoto. There is almost no limit to the type and range of lenses that can be used. The SLR can also be adapted for use on microscopes, telescopes, or other optical instruments. Also, filters can be installed on the lenses. Filters can change the amount of light entering the lens. For cameras like the XG-M that use through-the-lens metering. the system automatically compensates for the filter in most cases. Relatively inexpensive teleconverters can be used to multiply the focal length of existing lenses, at the expense of lens speed. Closeup lenses can be attached to the front of lenses, which reduces their minimum focus distance.

The disadvantage of SLRs is that they tend to be more expensive, bigger, and heavier than most point-and-shoot cameras. The complicated shutter and mirror mechanism tends to be noisier than simple in-lens shutters. Also, manual focus cameras are more difficult to use for catching action shots, especially where the subjects are constantly moving. Auto-focus SLRs are available, but they are expensive. Thus for casual use, hiking pictures, and taking pictures of children playing, SLRs are at a disadvantage. However, for the ultimate in flexibility and creative control for serious photography, SLRs are unsurpassed.


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Automatic Flash


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Note: I originally made this page for my son, who was taking a photography class and needed to know how to use my old Minolta XGM SLR camera. The f1.4 lens originally belonged to my father's classic Minolta SR-3, which had a clip-on selenium light meter. The SR-3's shutter finally died, so I bought an XG-M body and adapted the very fast f1.4 lens to it by adding a tab to the aperture ring.

Updated 9/19/05 by Ronald Horii