Souwalker wrote in post #4305409
I understood that f.5.6 is good for 1 subject but if I used f/5.6 in a group of 3 subjects, the middle subject is always in focus but the other 2 is slightly out of focus. How do I get all in focus? I read somewhere in this that f/8 is good for more then 1 subject but that's what I did and I still got one subject slightly blurred.
does the aperture speed have any bearing to the amount of light getting in?
It depends on how far you are away from the subjects, the focal length of the lens, and most importantly, how far the subjects are from each other front to back. There are lenses out there that have curved planes of focus as well, but that is a whole different kettle of fish. A smaller aperture (larger f/stop number) increases depth of field (the depth of what is in perceived to be in focus). So, f/8 has increased depth of field over f/5.6. Is either one of those values providing enough depth of field? It depends. I used to shoot a group of about thirty kids lined up on three or four steps at the front of a church sanctuary. I shot at f/5.6 with a 35mm lens and everyone was in reasonable focus. Using the same lens at the same aperture, if I were to get closer so that I only had three kids in the shot, one on each step, probably only one would be in sharp focus. Lots of factors enter into this.
As to your other question, an iris diaphragm forms a hole in the center of the lens that is the aperture. At f/8 the hole is smaller than it is at f/5.6. The smaller hole lets in less light. In fact, the amount of light between f/5.6 and f/8 is exactly half or, in photographer's shorthand, one "stop." The "stop" expression came from the fact that lens manufacturers in the good old days put a click stop on the aperture adjustment ring at these 1/2 values. So to answer your second question, yes, adjusting the aperture does adjust the amount of light going through the lens and that includes when using flash.
It occurs to me that modern cameras don't make the aperture very obvious because they only close down for the instant of the shot. The exception is in those instances where the camera has a depth of field preview and you use it while looking at the lens from the front. The result is that you never actually see the iris diaphragm that makes f/stops so obvious and relatively easy to understand. I suspect there isn't an old timer out there that didn't take his/her lens off and play around with the iris diaphragm just because it was cool to look at. So far, that is about the only advantage I see in being an old geezer.