In "plain speak" would be good!
Thank you,
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Photograhers, can someone please explain F numbers to me.
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Posted 2 years ago #
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F numbers tell you how much light the lens allows through to the sensor or film to make an image. They work like a 2 times table, so every "stop" (or move from one F number to the next) will allow twice as much light through as the one next to it when making the aperture (light hole) bigger, and half as much light when making the aperture smaller. The tricky thing is that instead of having sensible numbers like 1,2,3,4, etc F stops have silly designations that generally run from, say, F1.4, F2, F2.8 and so on up to somewhere around F16 or F22 (depending on the type of lens). In short, the smaller the number, the more light gets in, and the bigger the number, the less light gets in.
Posted 2 years ago # -
Raindog, not sure about your 2x tables but mine go up in two's, not doubling each time? Does each stop double the amount of light allowed or does it allow a fixed extra amount of light through?
(I also play with the apature setting on the camera but don't really understand how it does what it does).Posted 2 years ago # -
Small F number: Aperture is a really big hole. Small/short depth of field, i.e, only the object in focus is clear, background and foreground blurred. Lots of light let in, so can use a shorter exposure (of that's what you want), or get a picture in low light.
Large F number: Aperture is a really small hole. Large depth of field, i.e everything can be clear. Less light let in, so can need a longer exposure.
Posted 2 years ago # -
Ahhh, hang on
f1 = 2 1x2=2
f2 = 4 2x2=4
f3 = 6 3x2=6
so f2 gives you twice as much light at f1? But does f3 give you twice as much light as f2?
Or is that why they are f something.something instead of whole numbers?Think I will stick with experimenting rather than knowing
EDIT-bensales, that is what I got from experimenting, f number = depth of field, small to large. Good enough for a mildly and intermittently enthusiastic amateur.
Posted 2 years ago # -
F stops work like shutter speeds - they double up every time - 1/30th, 1/60th, 1/125th, 1/250th etc.
Posted 2 years ago # -
There are some really good tutorials on talkphotography that can explain much better than I can - I would link directly, but you have to log in to the site to view them, and I got shouted at last night for linking to pages that required that much effort
If you're interested it's worth a look.
Posted 2 years ago # -
Each 'stop' is a factor of 2. So each stop going up (from 1.4 to 2, from 2 to 2.8, from 2.8 to 4 etc) halves the amount of light coming in.
I tend to apply some simply mental rules to my pictures... do I want a shallow depth of field (e.g. a portrait) or do I have low light? Large aperture (small F-number). Do I want a large depth of field (e.g. a landscape) and/or do I have loads of light? Smaller aperture (large F-number). Then I play around with the shutter speed to get the exposure right (or in reality stick the camera in P-mode and let it figure it out :-))
Posted 2 years ago # -
Tracker it is the other way around. The lower the F the more the light that passes through the lens. And the F is not a silly number there is a logic behind the numbers.
Also double the number does not mean half the light. Each step means half the light so 1.4 lets in twice as much light as 2 and 2 lets in twice as much light as 2.8 . That is the aperture setting which you are playing with.
As bensales explained a side effect of changing the aperture is that it changes what is and isn't in focus in your picture.
Posted 2 years ago # -
Thanks everyone, I think I get it now.
BB
Posted 2 years ago # -
f numbers represent the size of the aperture, the hole that allows light through to the sensor or film. Small f numbers mean a big hole, so they let more light through and you can use faster shutter speeds. This has the effect of giving a shallow depth of field, ie how much of the shot will be in focus, with the background and foreground blurred. Big f numbers mean small holes, so you need to keep the shutter open longer to let as much light in. More of the shot will be in focus as the depth of field is much greater.
Prfoessional glass tends to be big and expensive to get those elusive small f numbers (most of my zooms are a constant f2,8 through their range, but they are eye wateringly expensive), unless its a prime (non zoom lens) which are much less complicated and tend to be cheaper. A 50mm f1.8 is a very good starting point for a large aperture lens. Lots of light gets in, some very shallow DOF shots are possible and they tend to be about £80, bargain!
There is also a "sweet spot" where a lens performs at its best. This is usually around f8. There's also the complicating factor of chromatic aberrations at very small apertures, usually f13 and smaller.
If your camera has an aperture priority mode, then you basically choose the depth of field by choosing the f number, and the camera will do all the maths to work out your shutter speed. Hold the camera still, and change the f number and watch the effect on the shutter speed.
Posted 2 years ago # -
Wiki is your friend...
Posted 2 years ago # -
pick up an old zenit fully manual camera, pop down to some pound shop and pick up a load of film, set aside about £50 for processing and go out and have fun, you'll see the change as you adjust the lens and it'll help you get a natural feeling as to what you need to use for what conditions
Posted 2 years ago # -
Have a look at these if you want a play as to how F-number, shutter speed and ISO are linked, they helped me get it.
http://www.kamerasimulator.se/eng/?page_id=2
http://www.camerasim.com/SLRsim.htmlPosted 2 years ago # -
http://www.morguefile.com/docs/Jodie_Coston:_Lesson_2
have a look here ^^^^^
Posted 2 years ago # -
Did anyone mention the rule of Reciprocity?
Posted 2 years ago #
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