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Subject: "Standard f-Stops" Previous topic | Next topic
dperry23 Registered since 02nd Mar 2013Sun 10-Mar-13 04:24 AM
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"Standard f-Stops"


US
          

According to my calculations, 2.8,4,5.7,8,11.3,16, and 22.6 should be the standard f-stops that half or double area of the diaphragm. How did we get the standard f-stops we have, and did we come to expect they half and double light on sensors?

  

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Replies to this topic
Subject Author Message Date ID
Reply message RE: Standard f-Stops
briantilley Moderator
10th Mar 2013
1
Reply message RE: Standard f-Stops
dperry23
10th Mar 2013
2
     Reply message RE: Standard f-Stops
briantilley Moderator
10th Mar 2013
3
Reply message RE: Standard f-Stops
jrp Administrator
10th Mar 2013
4
Reply message RE: Standard f-Stops
Digital_Reality
20th Mar 2013
5
     Reply message RE: Standard f-Stops
JosephK Silver Member
20th Mar 2013
6
          Reply message RE: Standard f-Stops
Broadway Bob Gold Member
21st Mar 2013
7

briantilley Moderator Deep knowledge of bodies and lens; high level photography skills Nikonian since 26th Jan 2003Sun 10-Mar-13 08:42 AM
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#1. "RE: Standard f-Stops"
In response to Reply # 0


Paignton, GB
          

Welcome to Nikonians

Successive f/stop values do indeed represent a halving (or doubling) of the area of the lens' diaphragm opening, and therefore a corresponding difference in the amount of light transmitted. That's assuming that the lens is correctly adjusted, of course

The standard numbering sequence is:

1 - 1.4 - 2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22 - 32 - 45

The "odd" numbers in the sequence (1.4, 2.8...) have always been rounded for convenience.

Brian
Welsh Nikonian

  

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dperry23 Registered since 02nd Mar 2013Sun 10-Mar-13 10:25 AM
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#2. "RE: Standard f-Stops"
In response to Reply # 1


US
          

I figured out the error in my calculations. I was using radius in places where I should have been using diameter. Thus,1.4, 2.0, 2.8, 4.0, 5.7, 8.0, 11.3, 16.0, and 22.6 are what I get for the exact doubling or halving of light. Now, I am trying to figure out where f-1.8 comes from and how lens makers get away with the cost difference between 1.8 and 1.4. It seems just as easy to make diaphram elements that go open up to either.

  

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briantilley Moderator Deep knowledge of bodies and lens; high level photography skills Nikonian since 26th Jan 2003Sun 10-Mar-13 10:36 AM
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#3. "RE: Standard f-Stops"
In response to Reply # 2


Paignton, GB
          

Lenses (or most of them, anyway) are not limited to full-stop steps in aperture. An f/1.8 lens is two-thirds of a stop slower than an f/1.4 lens.

The difference between lenses of f/1.8 and f/1.4 is not really in the physical diaphragm itself.

As the aperture opening gets larger, lenses tend to need a more complex (and hence more costly) optical design in order to deliver good image quality when used wide open.

Brian
Welsh Nikonian

  

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jrp Administrator JRP is one of the co-founders, has in-depth knowledge in various areas. Awarded for his contributions for the Resources Charter MemberSun 10-Mar-13 10:37 AM
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#4. "RE: Standard f-Stops"
In response to Reply # 0
Sun 10-Mar-13 10:38 AM by jrp

San Pedro Garza García, MX
          

These are the true values (with four decimals precision) of the standard apertures:

1.4142
2.0000
2.8284
4.0000
5.6568
8.0000
11.3137
16.0000
22.6274
32.0000

rounded, as Brian mentioned, for convenience

Have a great time
JRP (Founder & Administrator. Nikonian at the north-eastern Mexican desert) Gallery, Brief Love Story, The Team
Join the Silver, Gold and Platinum members that help this happen; upgrade. Join your personal web site to the Nikonians WebRing
Make sure you check our workshops at The Nikonians Academy and the product catalog of the Photo Pro Shop

  

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Digital_Reality Registered since 19th Oct 2012Wed 20-Mar-13 03:15 PM
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#5. "RE: Standard f-Stops"
In response to Reply # 4


Bangalore, IN
          

Aah thanks. Didn't know that

  

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JosephK Silver Member Fellow Ribbon awarded for his excellent and frequent contributions and sharing his in-depth knowledge and experience with the community in the Nikonians spirit. Nikonian since 17th Apr 2006Wed 20-Mar-13 11:34 PM
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#6. "RE: Standard f-Stops"
In response to Reply # 5


Seattle, WA, US
          

It all revolves around the square root of 2 and its multiples.

---------+---------+---------+---------+---------+
Joseph K
Seattle, WA, USA

D700, D200, D70S, 24-70mm f/2.8, VR 70-200mm f/2.8 II,
50mm f/1.4 D, 70-300mm f/4.5-5.6 VR, 18-70mm f/3.5-4.5 DX

  

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Broadway Bob Gold Member Nikonian since 15th Mar 2009Thu 21-Mar-13 12:02 AM
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#7. "RE: Standard f-Stops"
In response to Reply # 6


Groveland, US
          

Another factor to consider is the equation which includes the focal length of the lens: lens focal length/diameter of the aperture = f-stop. The f-stop number is a convenient way of describing the exposure settings rather than noting the area of the aperture. And, a given f-stop produces the same exposure regardless of the lens focal length (for a given shutter speed). For example, 1/500th of a second at f/5.6 on a 50mm lens gives the same exposure as those settings on a 300mm lens.

This becomes obvious if you think about an exposure meter - it only gives shutter speed and aperture regardless of the lens or camera type.

Bob

Visit my Nikonians gallery.

Visit my Nikonians gallery.

  

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