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Ordered a Chinese cable? I thought any camera shop would have one one the shelf... I have about 3 lying around somewhere...
Film - depends on what you are taking photos of. For bright objects - the moon and palnts - hey, they are in full sun! - then fine grain film is good as you still get reasonable shutter speeds and with fine grain you can enlarge then more. You can get tables in various books that tell you the correct shutter speed for film/f-ratio combinations for the various objects. Have alook in a library.
For deep sky, faster film is generally better.
As for f-ratio - if it's prime focus, then the f is the telescope f - so f5 or whatever. If you use a barlow or teleconverter, say a 2x, then add a stop or so - but it actually depends on the lens - film distance.
For eye-piece projection, the f-ratio is still f = focal length / diameter, but here it is the 'effective focal length'. There is a bit of maths involved, but you can approximate it by assuming that you get a magnification of 1x with a 50 mm lens on a 35 mm camera. Now if you have a 8" (200 mm) f5 with a 10 mm eyepiece, visually you will get (200 x 5) / 10 = 100 x magnification. But photographically, the magification is also multiplied by the ratio of the objective focal point to eyepiece : eyepiece to focal plane distance.
Confused yet?
Anyway, is this second magnification is 5x, then your overall magnification is 500 x or the equivalent of a 500 x 50 = 2500 mm lens. So now your effective f-ratio is 2500/200 = f12.5.
Probably best to get a book on the topic....
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