Aperture

OK, on all lenses we get the aperture (ex : F4-5,6) value of this lens. What I wanna know, is what does the aperture change? I know it means the opening of the diaphragm, but is a low aperture good or bad, and what kind of aperture should we except from a good pair of tele and macro lenses?

it adjusts how much light is let in, like at night or when I'm taking action shots, I use a lower aperture, but that's about all I know about it

a low aperture is neither good nor bad...it just is. if you are taking pictures in bright light, THEN it would be good, but if you are in poor light, it would be BAD...think of it like your iris...if it were the same and never moved, you would be blinded every time you went outside, and you wouldnt be able to see a thing after 7:00 at night. the higher the aperture, however, the less quality, simply because of the physics of light, which is totally something else.

also, you cant really expect to find a number in terms of a "good aperture", its all about experimentation. shutter speed also plays a role, as does the iso, how far you're zooming, etc. you should at least get a camera with an adjustable F-stop, so you can play around with the aperture to get a picture the way YOU think looks good.

You do want a lower aperture setting for the most part... Many cameras get very high on the end of the telephoto. As the camera compensates for this, you get longer shutter times, so you have to hold the camera more steady or you get blurry images... I know my Casio EX-50(I beleive that was the model) was particually bad at anything beyond full wide angle...

How would a 350 D perform in such a matter with an F4-5,6 (tele) and F2,8 (Makro) lens?

that last question didnt make much sense. Also remember that with a "larger" aperature number the actual size of the aperature becomes smaller. The numbers represent fractions of an inch, im not completely sure of that. Changing the Aperture also changes the depth of focus. Meaning the higher number Aperture will give you more focus infront and behind the subject that your shooting. also as Krimson King said the aperature is only one part of the whole shooting process, which includes ISO setting, Flash, zoom and shutter speed.

Aperture settings can work in your faour several ways. The higher the arperture setting(smalest number) the geater the depth of field which means the distances objects will be in critical focus. Letssay aperture setting of f 16 gives you a critical focus from 6 ft to infinity. Great setting when youwant everything crisp and clear... Contrary, an apetrure setting of 2.8 reduces your critical focus to about three feet before and after the main subject.

Example: You want a sharp picture of a beautiful rose bush ten feet away but not the old rundown outhouse 30 feet behind the rose bush...use wide aperture... Bush in focus....shithouse blurry.