>> Also, how does f ratio effect magnification.
The focal ratio itself does not affect magnification. (That is, you cannot tell how much magnification an F 4.5, for example, will give you.) However, FR is calculated in a simple formula of:
focal length / aperture = focal ratio
And FOCAL LENGTH does affect magnification. The longer the focal length, the more magnification for a given eyepiece. Therefore, WITH A GIVEN APERTURE, making a longer focal length will give you a longer focal ratio and more magnification. This means with a given aperture, a longer focal ratio will give you more magnification.
>>It seems that "planetary" scopes have high f ratios(a TEC 8 is around f/12) while some APO refractors are running around f/5 or f/6.
The planets are fairly bright objects that need a lot of magnification. Therefore, they benefit from the longer focal length, and don't need as much aperture. Apply the formula for FR, and you can see that means a higher focal ratio is OKAY. In addition, with a longer focal ratio, it is easier to remove chromatic abberation, false color. So, a relatively inexpensive achromatic telescope can function very well as a long focal length (and long focal ratio) planetary scope. An APO, however, does not need the longer focal ratio to overcome the false color problem so you can use them at slower, wider f ratios. And, since they are often better made, you can go ahead an use a shorter eyepiece to get the magnification equivalent to a longer focal length achromat.
>>but why is a high f scope slow to collect an image on a film/ccd-i
I'm not sure what you mean by "high f scope." The F10 scope has a higher F number, but I am not sure that makes it a high F scope. Most photographers would rather use a low F ratio scope (smaller F number) if possible since it shortens the exposure time. But for planets, for example, you will get ridiculously high equivalent F ratios (take a long F ratio scope like an SCT at F10, and then put a Barlow in it, making it F20 or slower) to get the magnification. At any rate, as to why the F ratio matters to a photographer, just realize that all the light you can get to your CCD, or Film, or other sensor, comes through the front of the scope (aperture). At that point, you have X number of photons to make an impression. If you magnify that light by a factor of two you will have one fourth of that number of photons on a given area of sensor. The lower F ratios magnify the light less. (Or, for a given focal length, have much wider aperture to let in more photons..)
Alex
