PDA

View Full Version : F-Stop on lens and camera



ktixx
12-14-2004, 03:00 AM
from my understanding, the F-Stop on a lense lets more light into the camera, it seems that the lower the F-stop the more epensive the lense. So it seems that Lower F-stops = better. Why then, and in what situations, would you want to use a higher F-Stop setting on your camera? What type of effects would you be looking to achieve and in what situation would you use a higher f-stop?

Ken

erichlund
12-14-2004, 08:24 AM
Lowest numerical f-stop is wide open and gives smallest depth of field. Depth of field is the range of depth that is "apparently" in focus, though there is really only one true focus distance. The largest numerical f-stop gives the greatest depth of field. Fixed focus lenses on cheap cameras have small apertures (high f-stops) so that they have a very wide depth of field. Lenses are typically designed to give the least distortion and other errors in the middle of their range, so unless you need the light gathering of a wide open lens or the depth of field of a stopped down lens, you want to work in the middle of the range, from f8 - f11.

You can, of course, use this information to creative advantage. On a portrait, you want to focus on the subject, but you don't want the background in focus, so open the lens up to blur the background. On a landscape, you "typically" want as much depth of field as you can get, so close the lens down.

Cheers,
Eric

ktixx
12-14-2004, 11:51 PM
Thank you very much, your reply definitely cleared things up. Basically if I want the full frame to be in focus (Landscapes) I have to use a higher F-stop, for portraits or close ups use a lower F-stop and in conditions when I am in low light the lower f-stop will be better. Did I get that all right?
Thanks again for your reply
Ken

Bryanj
12-20-2004, 07:41 PM
You may also want to use a slower shutter speed (capture flowing water etc), but then you risk over exposing the picture. You can compensate this by selecting a smaller aperture (bigger f/stop).
cheers Bryan :)

ReF
12-21-2004, 12:05 AM
Thank you very much, your reply definitely cleared things up. Basically if I want the full frame to be in focus (Landscapes) I have to use a higher F-stop, for portraits or close ups use a lower F-stop and in conditions when I am in low light the lower f-stop will be better. Did I get that all right?
Thanks again for your reply
Ken

I believe you are getting into a grey area when you are talking about low light and apertures. using a larger aperture in low light will allow you to use a faster shutter, but the way that points of light appear in night photography changes with the aperture setting. small apertures make points of light appear more focused and in a "star" shaped figure. with larger apertures, light appears more like "glowing orbs,'' but this glow can easily be too much and bleed into other parts of your picture. go outside and shoot a few pictures of the street lights at night. take one at the largest aperture, one in the middle of the range, and then with your smallest, then you can see for yourself what they look like. i personally prefer to use the small apertures for nightime photography, but sometimes with close up light sources i use larger apertures for a more dramatic effect. higher ISO settings have the same effect as higher f-stops on light sources (with digital cams at least) but there usaully isn't a need for higher ISO if tripods are involved anyways.