1. The oft-quoted 1.6x "crop factor" has nothing to do with viewfinder coverage. What you see in the viewfinder is almost everything you will capture in the image, save for a small margin around the edges.
2. No. The viewfinder will match (mostly) the captured image area, no matter what SLR camera you use.
3. Think of it this way. A given lens will cast a spot of light onto the focal plane, which contains the projected image. That circular spot of light is the same size for all EF lenses, but for EF-S lenses, it is smaller. In order to record the projected image, you could put a piece of light-sensitive film there, or in the case of a dSLR, you could put a digital electronic sensor. Imagine putting a rectangle inside a circle so that the two figures share a common center. If the rectangle is much smaller than the circle, you capture only that small central portion of the image. If the rectangle is made larger than the circle, then parts of the sensor will not be exposed to incoming light, leaving it black. Now if you make the rectangle so that its diagonal roughly matches the circle's diameter, then you are capturing as much as you can of the circle whilst ensuring the entire sensor is exposed to light.
How this relates to the crop factor is this: The EF lenses were made to accommodate 35mm film, so they project an image circle that is large enough to completely cover a rectangle of width 36mm and height 24mm. This is also the size of a 35mm "full-frame" digital sensor. Now, some sensors are smaller, and the ones used in some Canon bodies are called APS-C format. Just like the example I previously described, you can still use the EF lenses because all you have done is made the sensor smaller, and thus you are only capturing the smaller central portion of the available light. However, Canon has also made EF-S lenses, and these can ONLY be used with APS-C format sensors, because they project an image circle that is too small to expose a 36x24mm rectangle.
When we speak about focal length, we are talking about an intrinsic optical property of the lens, and the lens alone. Thus, a 50mm lens is always a 50mm lens, regardless of what you have used to capture the image that lens has projected. You could modify the focal length of the system by adding other optical elements or changing their position relative to the focal plane, but the fact remains that the size of the recording format is unrelated to the focal length.
However, the apparent angle of view of the captured image *does* depend on what we use to capture the image. If you use a small sensor, the angle of view is narrower than if you use a large sensor. This is what the 1.6x crop factor is for. If you use a 50mm lens on a "full-frame" body, in order to get an image with the same angle of view on an APS-C body, you would need to use a lens with focal length 50/1.6 = 31.25mm.
4. Please see my response to item 3 above. Again, you are misunderstanding the meaning of this 1.6x factor. It has nothing to do with viewfinder coverage--what you see in any SLR viewfinder will always closely match what you will capture in terms of coverage. The only thing the 1.6x factor does is tell you what focal length is needed in order to achieve the equivalent angle of view between an APS-C sensor and a 35mm sensor. If you don't own both formats, then you have no need for this so-called "crop factor.
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Originally Posted by wickerprints
