F-stops - What does it mean? - DPChallenge Forums

Olympus 40-150mm f/2.8 PRO M.Zuiko

09/15/2006 06:04:31 PM · #1

I've been using cameras for a while, and am aware of most of the terms related to photography, but have never understood the concept of f-stops. I've heard the term thrown around, and that you lose a stop with a certain lense or something. Can someone please help explain?

Thanks in advance.

Brad

Olympus OM-D E-M1

09/15/2006 06:10:37 PM · #2

More than you could imagine about f-stops

breadfan35

Nikon D3

Nikon AF-S Nikkor 50mm f/1.4G

09/15/2006 06:11:17 PM · #3

F-Stop = Aperture size

fotomann_forever

09/15/2006 06:13:51 PM · #4

F-number

Aperture

Hope those help.

fotomann_forever

09/15/2006 06:15:20 PM · #5

Originally posted by breadfan35:

F-Stop = Aperture size

Yes, aperture size is part of the equation, but also includes focal length.

f/# = f/D, where f = focal length and D = aperture diameter.

F-number is a universal way to measure the amount of light hitting the sensor or film at any given time.

Message edited by author 2006-09-15 18:18:37.

Canon EF 24-105mm f/4.0L IS

09/15/2006 06:26:18 PM · #6

I kinda understand now. I still don't understand how one can lose a stop. Are there any conditions that can cause this, or certain lenses?

slide12345678

Canon EOS-5D

09/15/2006 06:29:58 PM · #7

you don't exaclty LOSE a stop, you can either be above a certain f-stop or below a certain f-stop (i.e. you meant to shoot something at f5.6, but your camera was actually on f2.8, so you photo was overexposed by 1 f-stop)

what you may be referring to in terms of lenses is that not all lenses have the capability of doing f2.8, for example. so in those terms i suppose you would "lose" a stop (or "lose" the ABILITY to shoot at that f-stop)

Message edited by author 2006-09-15 18:31:35.

Sigma 24-70mm f/2.8 EX Aspherical DF for Canon

09/15/2006 06:35:02 PM · #8

So in other words, if I have a lens that says 1:3.5-5.6, it means that the lens' maximum aperture is 3.5, and it cannot go lower.

Message edited by author 2006-09-15 18:35:42.

hankk

Canon EOS-5D

09/15/2006 06:35:50 PM · #9

one additional f-stop gives twice the light (the diameter of the effective aperature is square root of two, or 1.4 times as big)

The equation you need to know is
1 f-stop = 2 x shutter speed = 2 times iso

There are a couple ways I know of to lose a stop (other than adjusting the aperature)
1. use a neutral density filter or a polarizing filter
2. use a teleconverter. 1.4x converter loses 1 stop, 2x converter loses two stops. That is, an f/2.8 lens loses two stops with a 2x teleconverter to have a maximum aperature of f/5.6.
3. have tons of dust on your sensor :-)

Message edited by author 2006-09-15 18:37:21.

Ecce_Signum

Canon EOS-5D Mark II

Canon EF 17-40mm f/4.0L USM

09/15/2006 06:36:20 PM · #10

Its really not that difficult to grasp (after you understand it lol). You have been given a few links so here is another :)

btw, f5.6 to F/2.8 is actually 2 stops.

Baxter

Nikon D500

Nikon AF-S DX NIKKOR 18-140mm f/3.5-5.6G VR

09/15/2006 06:45:46 PM · #11

Hope you can make sense of this. You can "loose a stop" if you are you using a tel-converter. A 2X converter would increase the focal length by 2X there by reducing the aperture by 2 stops (f#=(fx2)/D. Different converters would give you the ratio of loss depending on the focal length increase. (a 1.7X converter would loose 1.7 f-stops) Another way to "loose a stop" is if using filters. Different types and strengths will cause a differnt amount of loss.

Bugzeye

Fisher Price Kid-Tough Digital

09/15/2006 06:49:21 PM · #12

not to make things even more confusing but you can lose an F Stop or a Step of light while using a 2X teleconverter as well. That is all I know about it.