 Roy Blinston |
F-STOPS Can someone tell me the correct full f-stops (ie: not the half stops). Are they... f2, f4, f8, f11, f16, f32, f64.... and the others such as f3.5, f6.3 etc etc only half stops??? IThis is something that has bothered me for years. (Roy)
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
A full f/stop is a f/stop that doubles or halves the light from the previous f/stop. So if you were at f/2.8, a full f/stop would be f/4. If you were at f/2.5, a full would be f/3.5. You've been bothered by how much is a correct full glass of water.
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Roy Blinston |
I must be thick or something.... I still don't get it. Your answer has confused me even more. You say if I am at f2.8 then a full stop is f4. But you also said a full stop would be f2.5 to f3.5. My old Pentax camera has f stops in the range f3.5, f5.6, f8, f11, f16, f22 ... then is it right to assume the "notches" inbetween these f-stops are half stops? (ie: inbetween f8 and f11 is about f9.5). However, my Fuji s7000 digital camera has different f-stops (ie: f2.8, f.3.2, f3.6, f4, f4.5, f5, f5.6, f6.3, f7, f8). This is even more confusing.
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Kerry L. Walker |
The answer Gregory gave is is the correct one but may be a too technical (don't mean to sound condescending). One stop difference will either halve or double your shutter speed, depending on the direction you are going. With your Fuji camera, the changes from f2.8 to f4, 5.6, 8. etc. are full stop changes. The numbers in between are 1/3 stop changes.
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
My bad, I'll try another explination. You're digital camera dosen't have an aperture ring like old cameras do, you set the aperture, and it communicates with the contacts in the lens when you take a picture to go to what the aperture is. So in the display, you see every f/stop you can set the lens to(even 1/3 f/stops). Old cameras had that ring you could twist, and it only had some numbers, but you could fell the notches in between for the half f/stops(back then, don't think they made lenses yet to set to 1/3 f/stops) You lens on your fuji has a maximum aperture of 2.8 Say right now you use it outside and at iso 100, your shutter speed should be 1/1000. Going a whole f/stop would be f/4, and you'll see the shutter speed would need to be set to 1/500, because a whold f/stop cut the light comming thru in half. So you double the amount of time. You see that you have two other numbers before you get to f/4, which means you can set your apature in thirds.(if you could only set it in halves, you'd only have one number betweeen the f2.8 and the f4) Now suppose it's slightly more light, and a shutter speed of 1/1000 with iso100 would need an apature of f/3.6. A change of shutter speed to 1/500 would be double the time, which is a whole f/stop. So a whole f/stop change from f/3.6 would be to f/5. The most common f/stops to make lenses are to start at either f/2.8, f/4, or f/5.6 Probably due to film speed being standardised, and focal lengths being fairly standardised.(everybody makes a 50mm, nobody comes out with a 57mm) So you have a lens that starts at f/2.8, going up the scale in whole f/stops are f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/64, f/90. But I have a 50mm lens which has a max apature of f/2.5 So starting from there and going up in whole f/stops I go to f/3.5, f/5, f/7.1, f/10, f/14....etc. But because I can go in 1/3 f/stops, I can start at f/2.5 and change a 1/3 f/stop and be at f/2.8, and from 2.8, I can go to f/4. A full f/stop isn't a concrete measurement like distance. An inch over a mile is more than a mile, regardless of direction, size of your feet. Lenses have a measured max apature because of their focal length, the size of it(compare the front part of a 400mm 2.8 to anything below 400mm that's also a f/2.8 lens) and combined with other things I'm sure I don't know about. So you were right, the notches were half stops, in that they were half way between the ones marked on your lens.
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John P. Sandstedt |
I can't believe the preceding answers from these experts. The sequence is f1.0, (1.4 or 1.7,) 2.0, 2.8, 4.0, 5.6, 8, 11, 16, 22, 32, 64. Note that every other f/stop is doubled [f/1.0 > f/2.0 > f/4.0 etc.; f/1.4 > f/2.8, f/5.6, f>11.0 etc. That's the full stop sequence. Or, it has been since I starting shooting in the dark ages, with my Minolta SRT 201. And, if you line up shutter speed [backwards, staring at 1/1000th sec.] at f/1.0, you start the Exposure Value Chart. It's this relationship that allows you to achieve the same exposure at a variety of f/stops.
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
Well you know what they say, believing is seeing. That's why 5.6 doubles to 11 and not 11.2 But you can look at it as how f/stops are usually noted on a lens, which is the 2.8, 4, 5.6,...etc. Or you can look at it as a whole f/stop is the difference between certain f/stops, which is the 2.5 to 3.5 Because f/2.8 at 1/000 and f/4 at 1/500, just like f/2.5 at 1/1000 and f//3.5 at 1/500.
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Michael H. Cothran |
Roy, you didn't know what you were getting into with this question. I'll be as simple as possible - Here is a list of f-stops. Not all are found on each lens - f1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64, 90. Each of these is a FULL stop apart. Period. Half stops and third stops would be intervals between these listed f-stops. For example, if you want to close down a half stop from f11, it would be designated as f13.5 on a digital readout, or on an older lens with an actual aperture ring around the barrel, it would be halfway between f11 and f16. Michael H. Cothran www.mhcphoto.net
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Kerry L. Walker |
Thank you, Michael, for your sucinct answer. I guess I did not really pay attention to Roy's original question. My bad.
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Kerry L. Walker |
Please excuse my spelling (typing) error (succinct, not sucinct). Type too fast with too little talent.
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Roy Blinston |
Thanks for all the big answers. I am slowly getting there mentally. I suppose because of the correlation between the f-stops and the shutter speeds the "real answer" is in the pudding - meaning I should draw up a chart and take note of the shutter speed with each change in aperture setting (to see the difference). If the shutter speeds halves or doubles, then this must be a "full" f-stop. Am I right in my thinking?
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Roy Blinston |
OK... so I have just done some tests of my own. Here are my results: f8 @ 80s; f7 @ 100s; f6.3 @ 125s; f5.6 @ 160s; f5 @ 200s; f4.5 @ 250s; f4 @ 320s; f3.6 @ 400s; f3.2 @ 500s; f3.1 @ 640s. The full f-stops appear to be: f8; f5.6; f4; f3.1 (all the others are 1/3rd stops). The only confusing reading off my camera was the massive difference in shutter speeds between f3.2 and f3.1 (500s to 640s). Maybe my camera is picking the nearest equivalent with the machanics it possesses. Who is right from the above replies?
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Roy Blinston |
My whole reason for asking the question in the first place was because my "teacher" at Photo School said the exposure is halved or doubled every time you make a "click" change to the aperture. Upon hearing this my mind began questioning it. My response was.... "aren't the clicks inbetween only half-stops"... and she said "no".
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Kerry L. Walker |
If she says the clicks between full stops are not half stops, what does she think they are?
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
On old cameras and lenses, there was a ring on the lens that you could change that had actual numbers for the f/stops on it, with a line to mark which one you had the lens set to. The numbers could start at 1.4, then go to 2, 2.8, 4, 5.6, 11, 16,...etc. You would feel a click each time you set it to that number. But if you turn the ring so that the line marks in between 2.8 and 4, you'd also feel a click. That's because at that apeture, you are a half stop above 2.8 and a half stop below f/4. Now because the 2.8, 4, 5.6 etc... were the only numbers that are visible on old lenses, you could say those are the whole f/stops, and the clicks in between the visible numbers were half f/stops. On new cameras where the f/stop is displayed in the lcd, you see a number for each f/stop when you turn the thumb dial. So you get 2.8, 3.2, 3.5, 4, 4.5, 5, 5.6, 6.3. That's why I said before that a whole f/stop is an f/stop that will double or half your exposure time. You still have f/2.8 at 1/1000 sec giving the same exposure of f/4 at 1/500 sec. A whole f/stop change in apeture. Just like f/2.5 at 1/125 sec would give the same exposure of f/3.5 at 1/60 sec. That's a whole f/stop change in apeture. So the old way had only certain numbers showing for apetures you could set, but you could set for an apeture that didn't display a number. Which were the clicks in between. On new cameras and lenses they display all numbers for apetures you can set, so you click the number changes.
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Roy Blinston |
I realise the basics now... but I think my teacher was still wrong as she made no allowance for digital cameras, and was talking in visible apertures on an old film camera with clicks... but said nothing about the "half clicks" inbetween). My original thinking some years back was f2, f4, f8, f16, f32, f64 were the normal f-stops (because the numbers made sense) and everything else inbetween were half-stops (ie: f3.5, f5.6, f11, f22 etc).
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
Well it's not because of digital, but new film cameras are like that. LCD display of apeture, but you get the point. But the teacher was wrong, but could be due to her misunderstanding the question, or perhaps she was thinking in terms of an old lens that you couldn't set in between the numbers shown on the lens.
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John P. Sandstedt |
Thanks Michael for agreeing with me. But, Roy, Gregory is still incorrect. And, it's all a matter of mathematics. The f/number [speed of the lens] is the ratio of focal length to diaphragm diameter, typically when the lens is focused at infinity. Thus, when one shifts from f/1.0 to f/2.0 [one full stop] there is a halving of the light passing through the lens to the film plane [or media.] When one changes shutter speed, from 1/500th to 1/1000th sec., there is half the time allowed for the exposure and that's also one full stop. Sorry, Greg, I can't answer you're sarcasm about doubling f/5.6 to f/11.2. In fact while your addition is correct - there's probably not enough room for another digit on the barrel of a lens. You might also ask why shutter speeds jump from 1/60th to 1/125th. Why not check out a good photography book [like the ancient Handbook of Photography by Aaron Sussman, 8th Edition, ca. 1973] - you'll find that this is the doubling/halving sequence. As I said earlier, my experience dates to the dark ages. But, the mathematics [or is it physics (optics)] doesn't change. Of course, there are a lot of "modern" books on photography that explain the f/stop and it's relation to shutter speed to achieve the Exposure Value Table. An, if you have an auto-focus camera, check the manual - for it includes a chart showing where the computer chip shifts controlled exposures based on Exposure Value. Again, the mathematical principle. Oh, by the way, this is also the reason why ISO film speeds follow the doubling sequence: ISO 100 > ISO 200 > ISO 400, etc. You get one stop extra speed with each change in ISO number. But the "number" is doubled!
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John P. Sandstedt |
Hey Everyone - Check out Jon Close's answer to the same question on the Traditional Side. He's gone one step further and reminder me of the square root of 2 [1.414.] His answer confirms Michael's and mine above.
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Roy Blinston |
Incredible! My original question I thought was "dumb" as I thought there was a simple scientific answer to it all that experienced people would be able to pass onto me. All the comments sound plausible, and make sense in their own right. Even my teacher had her own opinion... and this forum has brought up yet more opinions. Incredible. Now I am really confused.
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Roy Blinston |
How come if the "hole" is getting bigger (ie: f2 compared to say f8) that the number gets smaller. One would think it is the other way round. Or is it referring to the "planes of the shutter" getting smaller (meaning less of it and therefore letting in more light)? A circle of area is more difficult to calculate (ie: Pi) than say a "square" (wherein if both the dimensions are doubled, then the physical area is multiplied by 4, and not 2). This is an important factor when calculating image resolutions. Not wishing to stir up too many hornets.... what does "f" mean??? One would assume it has something to do with "focal" or "focus".
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Kerry L. Walker |
Roy, see Michael's original post above. It is not an opinion. It is a fact. If your teacher says differently, she is wrong.
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
Uh, John S., you might read what I said. I said twice that one f/stop change doubles or halves the light, which is why I gave, two times, the examples of the shutter speed doubling and halving. And already knew about changing iso numbers. Yes 100 doubles to 200, and yes I know that's just like a whole f/stop change. And I'll go ahead and tell Roy that the reason why the number gets bigger is because it's expressed as a ratio. Talking about f/stop number, not iso number. I'm not seeing why you didn't get what I was saying. If you say that f/2, f/2.8, f/4, etc. are whole f/stops, then fine. But that would be like saying that 1/1000,1/500, 1/250, 1/125 are whole shutter speeds. True they're the only ones that have been typically display in the viewfinder, but I wouldn't call 1/640 or 1/200 half a shutter speed.
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Kerry L. Walker |
Gregory, cool it. No one is arguing with what you said. Yes, the information you gave is correct that a one stop CHANGE doubles or halves the amount of light striking the focal plane. All Roy wanted to know were the standard, recognized and time honored f-stops, which also represent a doubling or halving of the light.
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
everybody's relaxed on my end, no need for you to be worried. Already told Mr. Roy I know he got the point.
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Roy Blinston |
Hi everyone.... thanks for all the info. The penny has finally dropped.
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BetterPhoto Member |
f1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64, 90. These sre registered in the hall of fame A small f/stop should be f/1 and a high f/stop should be f/90, but it aint and further more pictures should be round like my lenses
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Dwayne Barbee |
I f I am not mistaken the reason the number gets larger with the decrease in apeture size is because the f-stop is a ratio.....just my 2 lincolns worth.
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