I stumbled across this website/blog in which the developer has created some fabulous simulations to compare the outcome of and practice on:
focus/reframe technique;
how exposure compensation works & affects the image; and
how aperture-shutter speed-ISO relate to each other & affect the image.
If you are new to SLR use, do yourself a favor & check it out.
If you're an old pro - check it out anyway. It's kind of fun to play with. :)
Heres' the link:
http://camerasim.com/ :-D
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