How many f stops are between 1.4- 1.8- 2.8?

<p>How big is the gap between these 3 apertures? Is it half stop, one stop? I know f stops go 2- 2,8 - 4- 5.6 - 8 etc. But I do not know between the f stops I mentioned.</p>

<p>There is a full stop between f/1.4 and f/2. So, f/1.8 is half way between those two.<br /><br />With f/2.8 being a full stop tighter than f/2, that means that f/1.4 is pulling in four times the light as f/2.8.</p>

<p>f/1.4 to f/1.8 is 2/3 stop.<br>

f/1.8 to f/2 is 1/3 stop, so f/1.8 to f/2.8 is 1-1/3 stops.<br>

f/1.4 to f/2.8 is 2 full stops.</p>

<p>See here:<br>

http://en.wikipedia.org/wiki/F/stop#Typical_one-third-stop_f-number_scale</p>

<p >Hi Carlos,</p>

<p > </p>

<p >The f/number set of numbers (number set) seems weird. The idea is provide a method that permits photographer’s to open up or close down the camera lens with geometric precision. Because of the way films preformed the ideal sequence was thought to be a doubling or halving of the light energy allowed to play on the film. Now the lens acts much like a funnel gathering light. Meaning the larger the working diameter of the lens, the more light gathered. Conversely smaller diameters reduce the light energy gathered. </p>

<p > </p>

<p >Now the entry way into the camera is a mechanical device that mimics the human eye’s Iris. This is the colored portion of our eye named for the Greek goddess of the rainbow. The camera iris is more communally called a diaphragm. Since most diaphragms are circular holes we must fall back on circle geometry. Factoid: If we multiply the diameter of any circle by the square root of 2 we have calculated a revised diameter that is twice as big. Twice in this case is surface area. Stated another way, to double the light gathering power of a lens we multiply the current diameter by 1.414. We don’t need to be so exact so we can use a shortened value of 1.4. </p>

<p > </p>

<p >Conversely to reduce the light entering the camera by half, we multiply the current diameter by 0.707. This is the inverse of 1.4. We can also divide by 1.4 to get the same answer but the preferred way is multiplication by 0.707.</p>

<p > </p>

<p >With the initiation of electronic light metering and precision lens making, the f/number it became possible to fine-tune the diaphragm using 1/2 f/stop adjustments. The multiplier is the fourth root of 2 which is 1.189. For finer adjusts, how about 1/3 f/stop which uses the sixth root of 2 which is 1.122</p>

<p > </p>

<p >Full f/stop number set using 1.4 </p>

<p >1 – 1.4 – 2 – 2.8 – 4 – 5.6 – 8 – 11 – 16 – 22 – 32 – 45 – 64</p>

<p >Note each value going right is its neighbor on the left times 1.4.</p>

<p >Each number going left is its neighbor on the right times 0.707.</p>

<p > </p>

<p >½ f/stop number set using 1.189</p>

<p >1 – 1.2 – 1.4 – 1.7 – 2 – 2.4 – 2.8 – 3.4 – 4 – 4.8 – 5.7 – 6.7 – 8</p>

<p > </p>

<p >1/3 f/stop number set using 1.122</p>

<p >1 – 1.1 – 1.3 – 1.4 – 1.6 – 1.8 – 2 – 2.2 – 2.5 – 2.8 – 3.2 – 3.5 – 4 – 4.5 – 5 – 5.6</p>

<p > </p>

<p >Isn’t math fun?</p>

<P>(Moderator's note: The 1/3 f/stop number set has been corrected as per Paul's post below.)

<a href="http://www103.pair.com/parv/cgi-bin/fstop.cgi">F-Stop Listing</a> produces three lists in 1/3-, 1/2-, and 1-stop intervals upto a given f-stop (1-100). Formula is also there if one wants to calculate in, say, 1/10 intervals.

<p >The mechanical limitations of the gear train of the iris diaphragm system within the lens barrel prohibit making super fine adjustments. Likely 1/3 f/stop is the best one can expect. I have seen scientific instruments that permit adjustment in 1/6 f/stop increments but they are atypical. </p>

<p > </p>

<p >Additionally some display indicators on some digital cameras indicate a super fine f/number setting. Likely this is wishful thinking as it would likely cost thousands of dollars to deliver such precision. All you will ever need or ever be able to set will be 1/3 f/stop increments. </p>

<p > </p>

<p >Sidebar: Early lenses did not have an adjustable diaphragm. In 1858 Mr. John Waterhouse devised metal inserts that slipped into a slot in the lens barrel. These inserts came in a set with different size aperture holes. Because they passed some light and stopped some, they were called Waterhouse Stops. Today the Waterhouse Stop has been replaced by a mechanical iris consisting of thin overlapping metal leaves that mimic the human eye iris. </p>

<p > </p>

<p >The symbol f/number is an abbreviation or acronym for focal ratio. The f/number value intertwines the two major properties of a lens – focal length and working diameter. The f/number mergers these into a ratio (focal length ÷ working diameter). The f/number method assures that a lens set to say f/4 delivers the same light energy to the film or chip as any other lens so set, regardless size. Thus a lens 4 meters in diameter with a focal length of 16 meters delivers the same light energy as a lens 4mm in diameter with a focal length of 16mm. Both are set to f/4. </p>

<p > </p>

<p >Many attempts to simplify have been tried but optical engineers carry on the f/number system. Maybe you will be the one to hit upon a better method. </p>

<p>Alan, I think you made a typo in your second from last message. For the sake of good order 1/3 stops should be:</p>

<p>1 – 1.1 – 1.3 – 1.4 – 1.6 – 1.8 – 2 – 2.2 – 2.5 – 2.8 – 3.2 – 3.5 – 4 – 4.5 – 5 – 5.6</p>

<p>A tip of the hat to Paul. I stand corrected. I will sit in the cornor with my dunce cap on.<br>

See - us old guys (I'm 71) make more more and mistakes every day.</p>

<p>Thanks again Paul</p>

<p> </p>

<p>LoL! It's easily done Alan :o)</p>