EspenW Junior Member 28 posts Joined Dec 2006 Location: Oslo More info | Feb 10, 2007 14:27 | #1 I am reading Bryan Peterson's Understanding Exposures. Great book, and I also found some answers about F numbers, that I have been wondering about for a while.
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tsaraleksi Goldmember  1,653 posts Likes: 1 Joined Sep 2006 Location: Greencastle/Lafayette Indiana, USA More info | Feb 10, 2007 15:28 | #2 Why shouldn't it? --Alex Editorial Portfolio
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gjl711 Wait.. you can't unkill your own kill.  57,744 posts Likes: 4074 Joined Aug 2006 Location: Deep in the heart of Texas More info | Feb 10, 2007 15:38 | #3 Pretty simple and straight forward once it sinks in. Not sure why, but call me JJ.
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kevin_c Cream of the Crop 5,745 posts Likes: 4 Joined Mar 2005 Location: Devon, England More info | Feb 10, 2007 15:44 | #4 EspenW wrote in post #2686338  I am reading Bryan Peterson's Understanding Exposures. Great book, and I also found some answers about F numbers, that I have been wondering about for a while. He says: The diamteter of the aperture is the focal lenght divided by the F number. 50mm F2 = 25mm aperture diameter. This Sounds resonable. How about 16mm F22? Aperture diameter of 0.72mm!!! Can this be true? Espen Yep! (unless maths changed since I left school many years ago -- K e v i n --
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Bob_A Cream of the Crop  More info | Feb 10, 2007 15:45 | #5 Read this page, it may help things sink in: Bob
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Wilt Reader's Digest Condensed version of War and Peace [POTN Vol 1]  More info | Feb 10, 2007 16:30 | #6 EspenW wrote in post #2686338 I am reading Bryan Peterson's Understanding Exposures. Great book, and I also found some answers about F numbers, that I have been wondering about for a while. He says: The diamteter of the aperture is the focal lenght divided by the F number. 50mm F2 = 25mm aperture diameter. This Sounds resonable. How about 16mm F22? Aperture diameter of 0.72mm!!! Can this be true? Espen And now you understand where the topic of aperture-induced diffraction- limited lens performace has its roots! You need to give me OK to edit your image and repost! Keep POTN alive and well with member support https://photography-on-the.net/forum/donate.php
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Feb 10, 2007 16:53 | #7 Thanks everybody.
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thebigphil Member  95 posts Joined Jan 2007 Location: Dayton, OH More info | Feb 10, 2007 17:10 | #8 Until you start buying glass. Then this forum is the Devil -----------
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Feb 10, 2007 17:26 | #9 Are you yoking me man?
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Lord_Malone Cream of the Manpanties........ Inventor Great POTN Photo Book  7,686 posts Likes: 1 Joined Oct 2005 More info | Feb 10, 2007 17:33 | #10 Go to your local camera store and play around with the 16-35L (or similar). Mount the lens on your camera and select an aperture of f/22. Point the camera straight at you, look squarely into the lens opening. The lens will be stopped at 2.8 by default. Push and hold the depth of field preview button, and witness something very cool. ~Spaceships Don't Come Equipped With Rear View Mirrors~
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Feb 11, 2007 01:23 | #11 I just did that with my 24-105.
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Collin85 Cream of the Crop  8,164 posts Joined Jan 2007 Location: Sydney/Beijing More info | Feb 11, 2007 01:33 | #12 EspenW wrote in post #2688941 I just did that with my 24-105. Now I can see with my own eyes, what a 1.09mm aperture looks like. Cool! E Keep in mind what a 'f-stop' means in terms of practical photography. Each full f-stop changes the amount of light let through the lens by a factor of two. In other words, double or half. Col | Flickr
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Feb 11, 2007 05:37 | #13 No, I understand this now. It's only a ratio. Smaller hole, longer exposure time, and vice verca.
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JeffreyG "my bits and pieces are all hard"  More info | Feb 11, 2007 07:07 | #14 The diamteter of the aperture is the focal lenght divided by the F number. 50mm F2 = 25mm aperture diameter. This Sounds resonable. How about 16mm F22? Aperture diameter of 0.72mm!!! Can this be true? Almost true, but not quite. The f/# is the ratio of the inlet pupil to the focal length. The actual aperture diaphragm inside the lens is not necessarily the same diameter as the inlet pupil, all of which is governed by optics. A 50mm f/1.0 L does not necessarily have a 50mm maximum aperture diaphragm. It has a big enough aperture diagphragm to form a 50mm inlet pupil. My personal stuff:http://www.flickr.com/photos/jngirbach/sets/
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gjl711 Wait.. you can't unkill your own kill. 57,744 posts Likes: 4074 Joined Aug 2006 Location: Deep in the heart of Texas More info | Feb 11, 2007 09:27 | #15 EspenW wrote in post #2689464 What suprices me, is that a huge wide angle picture, full of colors and details can be exposed threw a 0.72mm pinhole. e Time to have some fun. Build yourself a pinhole camera. not quite the same thing as whats being discussed here, but you can get real nice landscape pictures through a little tiny pinhole with no glass at all. Not sure why, but call me JJ.
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