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My entire world is unraveling at the seams


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#1 Nick Norton

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Posted 08 August 2008 - 01:46 PM

BOREDOM ALERT:

This post is about F stops.


Ok, i thought i had this thing down to a science... but my mind started thinking (surprise)...
and i came to the realization that perhaps i have been wrong this entire time.

I understand one stop difference lets half or twice as much light to reach the film.

However, i always thought of this "stop" as a click on the f-stop ring. So 2.8 to 4 would be one stop.

But i started thinking, perhaps 2.8 to 5.6 is one stop... and 4 would be maybe a third of a stop difference?



So, my question... is say f4 to f8 a one stop difference, or is f4 to f5.6 a one stop difference.


Sorry for the ignorancy of this question-

Nicholas
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#2 David Mullen ASC

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Posted 08 August 2008 - 01:51 PM

The next stop after f/2.8 is f/4, then f/5.6, then f/8...
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#3 Nick Norton

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Posted 08 August 2008 - 02:05 PM

So why would "they" make it so damn confusing?

Why not have f2, then f4, then f8, then f16, and so on.

Why should every OTHER number double if not for the sole reason to make cinematography more confusing?
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#4 David Rakoczy

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Posted 08 August 2008 - 02:06 PM

Nick,

Stop whatever it is you are doing... order the book CINEMATOGRAPHY by Malkiewicz & Mullin (the above poster). Take a weekend and READ. STUDY. LEARN.... RE-READ... then, ask your questions.
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#5 K Borowski

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Posted 08 August 2008 - 02:09 PM

BOREDOM ALERT:

This post is about F stops.


Ok, i thought i had this thing down to a science... but my mind started thinking (surprise)...
and i came to the realization that perhaps i have been wrong this entire time.

I understand one stop difference lets half or twice as much light to reach the film.

However, i always thought of this "stop" as a click on the f-stop ring. So 2.8 to 4 would be one stop.

But i started thinking, perhaps 2.8 to 5.6 is one stop... and 4 would be maybe a third of a stop difference?



So, my question... is say f4 to f8 a one stop difference, or is f4 to f5.6 a one stop difference.


Sorry for the ignorancy of this question-

Nicholas

'

Why is science and optics subject to a boredom alert?! ;)

No, that is actually a common question, and I've seen it mentioned up front in many basic photography texts when F/stops are introduced.

The reason why 8 isn't half the light of 4 (it's 5.6 rather) is that you're dealing with circles. The F/stop equation basically measures (IIRC) the area, or is it diameter or radius, I forget now, of the stop, or hole in the lens that lets light onto the film or chip.

Because it's radius I think in the formula, and the formula is ∏R^2, you have to take the square root of the number. So, the progression is that of radical two rather than two. because the way the formula works the F/number is the square.

I really butchered explaining that, but I hope that clears it up somewhat for you. Now I gotta get!
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#6 Nick Norton

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Posted 08 August 2008 - 02:26 PM

Nick,

Stop whatever it is you are doing... order the book CINEMATOGRAPHY by Malkiewicz & Mullin (the above poster). Take a weekend and READ. STUDY. LEARN.... RE-READ... then, ask your questions.


I actually own and have read that book in its entirety once... and frequently go back to it. I know most of the fundamentals when it comes to cinematography, however my mind started going and i was unsure if perhaps i assumed too much and possibly looked over something. Unfortunatly, i am out of town at the moment, and unable to go back to "cinematography."

I also just realized that Mullen, THE David Mullen, is an active particapant here at cinematography.com... and holy sh**. All i can say is we are all very lucky to have such a community of professionals and newcomers alike to help/inspire/learn.

Long live cinematography.com!



'

Why is science and optics subject to a boredom alert?! ;)

No, that is actually a common question, and I've seen it mentioned up front in many basic photography texts when F/stops are introduced.

The reason why 8 isn't half the light of 4 (it's 5.6 rather) is that you're dealing with circles. The F/stop equation basically measures (IIRC) the area, or is it diameter or radius, I forget now, of the stop, or hole in the lens that lets light onto the film or chip.

Because it's radius I think in the formula, and the formula is ∏R^2, you have to take the square root of the number. So, the progression is that of radical two rather than two. because the way the formula works the F/number is the square.

I really butchered explaining that, but I hope that clears it up somewhat for you. Now I gotta get!



Thank you, that helped a ton.

-Nicholas
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#7 David Mullen ASC

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Posted 08 August 2008 - 02:47 PM

Some light reading... (pun unintentional)

http://en.wikipedia.org/wiki/F-stop
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#8 David Rakoczy

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Posted 08 August 2008 - 03:05 PM

David, please forgive my type-o... it is indeed Mull(e)n.

have a great weekend!
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#9 James Steven Beverly

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Posted 09 August 2008 - 02:41 AM

So why would "they" make it so damn confusing?

Why not have f2, then f4, then f8, then f16, and so on.

Why should every OTHER number double if not for the sole reason to make cinematography more confusing?

Because dude, it's a logarithm. It COULD be named stop 1, stop 2 stop 3, ect but it really doesn't matter. the smaller the number the larger the opening, it's that simple. A LOT of things in cinematography are logarithms so get use to it. Unless you're designing lenses, it's not really important that you understand ALL the science behind it, it's JUST important that you understand how it effects the shot, that's all. The numbers themselves are meaningless, what the numbers do to effect your frame is what is important. B)
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#10 Hal Smith

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Posted 09 August 2008 - 09:36 AM

Successive full stops are in the ratio of the square root of 2 to each other rounded off to one decimal place. 2 X 1.414 = 2.8(28), 2.828 X 1.414 = 4.0(00), 4.0 X 1.414 = 5.6(56), etc.
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#11 John Young

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Posted 11 August 2008 - 10:34 AM

Just for the sake of argument, and because I have nothing useful to add to this thread; I thought I would tell you the truth about that formula you typed up there.

∏R^2... however every one knows that Pie are round. I have never seen a square pie. So the equation should look like this:

∏R^∅... that's better, Pie are round.

Cobbler on the other hand IS square. Although as far as I know they have not made a math symbol for cobbler.
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#12 K Borowski

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Posted 11 August 2008 - 04:48 PM

Some light reading... (pun unintentional)

http://en.wikipedia.org/wiki/F-stop


I for one, do NOT believe that the pun was unintended :P
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