Roycruse, the MOST important rule in photography to remember is this:
The PHOTOGRAPHER takes the photograph, NOT the camera
You can take crap photos with a very expensive camera.
The next most important rule in photography is:
Only show people your BEST photographs
Learn from your disasters, but don't put them on show...
The third most important rule in photography is:
Go on an expedition with Photo4x4 if you really want to improve your photography...
This is a very BIG subject so I'll try to keep this as brief as possible (honest).
Depth of Field - This is directly affected by the aperture, the smaller the aperture the larger the depth of field (more of the picture in sharp focus), the larger the depth of field the more shallow the depth of focus (less of the picture in sharp focus). The smaller the number the larger the aperture, the larger the number the smaller the aperture. This is because the aperture number (also called f stop) is actualy a fraction. Therefore 1/2.8 th (f stop 2.8) is larger than 1/22 nd (f stop 22).
As you quite rightly say with an SLR camera, digital or film, you have much more choice as to how the final shot turns out than with an automatic compact type camera.
This shallow depth of field is most often used in portrait photographs, but can be used at any time when you want a particular item to stand out in your photograph.
As Codprawn says the 'fast' telephotos cost thousands of £s.
The convention is to use wide angle lenses (28mm up to 50mm) for landscape photography and with maximum depth of field. However conventions are there to be broken! The lens that I use most for landscapes (you can see the results on the website) is the 28-300mm. Most of the experienced photographers that I take out on expeditions are amazed by just what you can do by trying something different.
In perfect weather in perfect conditions the 'convention' is okay (a bit boring but it works) however in the UK conditions are not often perfect. Then it pays to have a few unconventional tricks up your sleeve. The telephoto zoom lens can be used to isolate detail and to emphasize aspects of the landscape.
I have another set of rules that I give to my customers:
Rule 1: There are NO rules
Rule 2: In case of doubt apply Rule 1
Photography is a fascinating subject and digital photography has boosted interest in it.
Digital photography is NOT an excuse to be lazy and take loads of shots so that one might just be okay.
Digital photography is however an ideal excuse to EXPERIMENT.
Remember that the Victorians produced some truly stunning photographs, and they did it with cumbersome plate cameras with the lowest of technology.
Keith (((auto bracketing
This photo was taken with a wide angle lens, thereby proving that I break my own rules...