Periodically photographers, including the author, are asked "which camera should I buy?"

• It is difficult enough for photographers to select their own equipment. How on earth can anyone know what will work for someone else?
• The appropriate equipment for one photographer will not necessarily be appropriate for another photographer because the end objective, subject matter, and shooting styles will differ.

The following discussion is based upon the demise of silver-based film photography and the inevitability of digital imaging.

Two characteristics of sensor size which are important are the number of pixels and the dimension of the sensor, usually expressed in millimeters.

Is your final output prints? If so: Digital prints are generally made at 300 dpi. The best quality prints come from a digital original where the pixels in the original equal the print size multiplied by 300. For example, if the largest size print needed is 8x10, then the optimum number of pixels is 2400x3000. If you never ever crop, then a sensor size of 2400x3000 pixels will be fine. If you crop frequently, a larger sensor size is needed.

Is your final output web only or email only? The world is you oyster. The sensor size does not matter much.

Will you be shooting at high ISO settings, such as ISO 400 and above? If so, a larger sensor size in millimeters is indicated. Refer to article on sensor size.

Understand the relationship between the diagonal of the sensor size in millimeters, the focal length of the lens, and the angle of coverage. Often focal lengths are expressed in their 35mm equivalent. Magnification factor is the expression of how much of the image will appear to be magnified (meaning cropped) (meaning less angle of coverage) compared to a full size 24x36mm sensor with a diagonal of 43mm. This is especially important for lens systems where the sensor size of bodies differ, such as Canon, Nikon, and Sony-Minolta. Refer to chart of 35mm equivalent lens coverage and article on sensor size. Some examples: A 50mm lens with a full frame 24x36mm sensor covers 47 degrees diagonally. The same 50mm lenses on a body with an APS-C sensor will cover 50x1.44="72mm 35mm equivalent" or a coverage of 33 degrees diagonally. Note: The 4/3 system has a multiplication factor of 1.92, but all of the bodies have the same sensor size, so 4/3 is always "full frame" for its type. However, a 50mm lens on a 4/3 camera would cover 50x1.92 ="96mm 35mm equivalent" or a coverage of 26 degrees diagonally.

Will interchangeable lenses be needed or will an all-in-one camera (often called point-and-shoot) be sufficient? The use of interchangeable lenses will dictate an SLR body.

Do you frequently photograph the interiors of bathrooms or other tight places? If so, wide angle lenses are important. If you also need interchangeable lenses, then it may be important to obtain a camera body with a full-frame sensor (magnification factor 1.0) rather than a sensor with a magnification factor greater than one.

Do you frequently photograph hummingbirds at distances of three miles or other subjects far away? If so, telephoto lenses are important.

Do you frequently photograph flowers, small plastic horse models, jewelry, or other really small things? If so, a macro lens is important. Generally a macro lens which is twice the diagonal of the sensor size works best because it allows longer operating distances. Therefore, an APS size sensor would work well with a 50mm macro lens, while a full-frame 35mm sensor would work well with a 100mm macro lens. (When expressed in "35mm equivalent," target 100mm focal length is appropriate for macro use).

Do you mostly intend taking pictures of Aunt Mildred and Uncle Harry? If so, the world is your oyster. The lens does not matter much.

Do you frequently take rapid sequence photographs, such as a runner sliding into second base? If so, the burst rate is important.

Do you already own Canon, Nikon or Minolta (now Sony) lenses which you wish to continue to use? If so, then select only SLR bodies which are compatible with the lenses.

A check of detailed specifications on a site like dpreview might suggest some features which are important.

From the list of alternatives there should be obvious comparison factors of cost-benefit, feature differentiation, etc. A check of detailed specifications on a site like dpreview will help differentiate among possible choices. Select the best fit.

If you still want to ask "But what camera do you use?" then you have missed the point of this article.