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Help needed on f-stops and iso

ukuwi 14 476 1 England
11 Jun 2004 9:29PM
Hi all, I have had my camera for a good few months now, and feel its about time I found out what an f-stop is and what does the iso do or mean, I see references to them all the time, so you lot obviously know how to use them.

anyone care to enlighten me?


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bppowell 16 2.2k 2 England
11 Jun 2004 9:39PM
ISO - this is a measure of the speed of the film.

If you shooting in low light you have to have a longer exposure, by increasing the ISO value it should make for a better result. Increase too much though and noise will spoil they result. So you have to find a happy balance.

F-Stop, This controls the diameter of the lens. Combined with the shutter speed they dictate just how the shot will be taken.

F-stop controls the depth of field by adjusting the amount and intensity of light getting through to the film/CCD and the shutter speed controls how long the light is allowed through for.

Hope this makes sense.

peterkin 14 637 England
11 Jun 2004 9:46PM
Are you joking, ukuwi? There's some great images in your portfolio. I particulary like "escape" and "clasico". I know about iso, f-stops etc but my images are rubbish compared with most of those in the gallery. Mmmmm.
ukuwi 14 476 1 England
11 Jun 2004 9:46PM
Thank you Barry for your post and knowledge, the ISO bit I can grasp, and it seems like I will have to do some trial and error, to understand it better, but the f-stop, whooosh, straight over my head, any chance of that in English, the shutter speed bit I get, but how do you know what f-stop setting to use, if possible, could you give me an example, thanks
ukuwi 14 476 1 England
11 Jun 2004 9:49PM
No Peter I am not joking, this is my first camera, And I use its point and hope mode.
FrankThomas 15 2.8k United Kingdom
11 Jun 2004 9:52PM
Think of a hose pipe, look at the shutter speed as the pressure of water flowing thru the hosepipe and the aperture as the diameter of the hosepipe. For any "Flow rate" (i.e. exposure) there are a number of different combinations of water pressure and hose diameter.

Normally you either pick the shutter speed and let the camera sort out the aperture or pick the aperture and let the camera sort out the shutter speed. If you want control of how the speed of something is recorded, either sharp or blurred then you set the appropriate shutter speed.

If you want to control the depth of field, then you pick whichever aperture gives you the DOF you want and the camera sorts out the rest.

If you want a shallow DOF then you set as wide an aperture as possible (F2.8 or so) but if you want the whole thing sharp front to back, then you stop the lens down to F22 or thereabouts

Hope that makes sense
ukuwi 14 476 1 England
11 Jun 2004 9:55PM
Yes Frank, I do understand what you are saying, does that have anything to do with f-stops, please excuse my ignorance.
ukuwi 14 476 1 England
11 Jun 2004 9:56PM
did you add that bit on the end afterwards, or did I just not read your comment properly, sorry for the mistake.
FrankThomas 15 2.8k United Kingdom
11 Jun 2004 9:58PM
the aperture is measured in F-stops - if you "stop the lens down" you set a small aperture (F22) and if you open it up, you set a wide one (F2.8)

The wider the aperture, the smaller the F number

(I added the last bit in the previous post - probably after you first read it)
ukuwi 14 476 1 England
11 Jun 2004 9:59PM
Ok, I mainly take portraits, and I want to have nice sharp shots, not bothered about dof, as my backgrounds are usually blank, so does that mean a higher value f-stop?, in auto mode, it normally reads 2.4.
peterkin 14 637 England
11 Jun 2004 10:00PM
Oh. Mine hasn't got a point and hope mode. So that's where I'm going wrong. Smile
FrankThomas 15 2.8k United Kingdom
11 Jun 2004 10:00PM
it depends on the camera - most of the "program" or "auto" modes will try and set as high a shutter speed as possible to minimise camera shake. For an ideal portrait, you want a wide aperture (2.4 or whatever it is) so that the background goes out of focus

(ps - Peter, Mine doesn't have point and hope either, it's manual or manual)
ukuwi 14 476 1 England
11 Jun 2004 10:02PM
I really do appreciate your help, I will keep coming back here while I experiment, but you have made things a lot clearer for me, many thanks to you all.
FrankThomas 15 2.8k United Kingdom
11 Jun 2004 10:03PM
no worries - took me ages to get the hang of it too
ukuwi 14 476 1 England
11 Jun 2004 10:05PM
one more quick question, do you alwys have to set your camera up each time before each shot, or do you set it once and away you go, I think this will take quite a bit of experimenting, thanks

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