The Foundation of Exposure
Dec 19, 2017 10:39:49 #
This subject has been covered from other angles but the following description might help make the subject clearer. I have summarized this from a PDF that I posted on my web site. The PDF and associated Excel spreadsheet in my next post.
To record a gray card as gray you need to balance ISO with exposure value (EV). EV is a combination of aperture and shutter speed so together ISO, aperture and shutter speed make up the exposure triangle.
The fundamental assumption underlying EV is that an exposure of 1 second at f/1 equates to an EV of 0.
An exposure of one second is given a value of 0. Each doubling of the shutter speed increases the value by one:
ISO can also be expressed it as a logarithmic series:
Recommended Exposure Values
You will often see published EV tables based on ISO 100. So long as you adjust for ISO, these can be used as a reality check or for actually getting a starting exposure in unfamiliar situations. For example:
* Taken from the Wikipedia article on Exposure value where you can find additional information.
To record a gray card as gray you need to balance ISO with exposure value (EV). EV is a combination of aperture and shutter speed so together ISO, aperture and shutter speed make up the exposure triangle.
The fundamental assumption underlying EV is that an exposure of 1 second at f/1 equates to an EV of 0.
An exposure of one second is given a value of 0. Each doubling of the shutter speed increases the value by one:
1 sec 1/2 1/4 1/8 1/15 1/30 1/60 1/125 1/250 1/500
0 1 2 3 4 5 6 7 8 9
An aperture of f/1 is given a value of 0. Each full stop of reduced aperture increases the value by one:0 1 2 3 4 5 6 7 8 9
f/1 f/1.4 f/2 f/2.8 f/4 f/5.6 f/8 f/11 f/16 f/22
0 1 2 3 4 5 6 7 8 9
The shutter speed and aperture values are added together to get the exposure value (EV). You can see how aperture and shutter speed are combined as EV in this table from the back of a Rolleiflex TLR:0 1 2 3 4 5 6 7 8 9
F: 2.8 3.5 4 5.6 8 11 16 22
1 sec 3 3.5 4 5 6 7 8 9
/2 4 4.5 5 6 7 8 9 10
/4 5 5.5 6 7 8 9 10 11
/8 6 6.5 7 8 9 10 11 12
/15 7 7.5 8 9 10 11 12 13
/30 8 8.5 9 10 11 12 13 14
/60 9 9.5 10 11 12 13 14 15
125 10 10.5 11 12 13 14 15 16
250 11 11,5 12 13 14 15 16 17
500 12 12.5 13 14 15 16 17 18
You can expose with an EV of 10 at several offsetting shutter speed and aperture combinations. In some film camera lenses (like Hasselblad) EV is mechanically linked so that you can change both shutter speed and aperture while keeping the EV constant. 1 sec 3 3.5 4 5 6 7 8 9
/2 4 4.5 5 6 7 8 9 10
/4 5 5.5 6 7 8 9 10 11
/8 6 6.5 7 8 9 10 11 12
/15 7 7.5 8 9 10 11 12 13
/30 8 8.5 9 10 11 12 13 14
/60 9 9.5 10 11 12 13 14 15
125 10 10.5 11 12 13 14 15 16
250 11 11,5 12 13 14 15 16 17
500 12 12.5 13 14 15 16 17 18
ISO can also be expressed it as a logarithmic series:
25 50 100 200 400 800 1600 3200 6400 12800
2 1 0 -1 -2 -3 -4 -5 -6 -7
When everything is combined:2 1 0 -1 -2 -3 -4 -5 -6 -7
1/500 sec 9
f/16 8
EV (subtotal) 17
ISO 400 -2
Total 15
f/16 8
EV (subtotal) 17
ISO 400 -2
Total 15
Recommended Exposure Values
You will often see published EV tables based on ISO 100. So long as you adjust for ISO, these can be used as a reality check or for actually getting a starting exposure in unfamiliar situations. For example:
EV Lighting Conditions*
16 Light sand or snow in full or slightly hazy sunlight (distinct shadows)
15 Typical scene in full or slightly hazy sunlight (distinct shadows)
Rainbows: Clear sky background
14 Typical scene in hazy sunlight (soft shadows)
Side lighting in full sunlight
Rainbows: Cloudy sky background
13 Typical scene, cloudy bright (no shadows)
Back lighting in full sunlight
12 Typical scene, heavy overcast, Areas in open shade, clear sunlight
Sunset
11 Subjects in deep shade
10 Neon lights at night
9 Night sports, ice shows
8 Night street scenes, window displays, circuses
7 Fairs and amusement parks at night
6 Home interiors
5 Christmas tree lights outdoors, night vehicle traffic, subjects lit by bonfires
4 Floodlit buildings, monuments and fountains
3 Fireworks
2 Distant view of lighted buildings
16 Light sand or snow in full or slightly hazy sunlight (distinct shadows)
15 Typical scene in full or slightly hazy sunlight (distinct shadows)
Rainbows: Clear sky background
14 Typical scene in hazy sunlight (soft shadows)
Side lighting in full sunlight
Rainbows: Cloudy sky background
13 Typical scene, cloudy bright (no shadows)
Back lighting in full sunlight
12 Typical scene, heavy overcast, Areas in open shade, clear sunlight
Sunset
11 Subjects in deep shade
10 Neon lights at night
9 Night sports, ice shows
8 Night street scenes, window displays, circuses
7 Fairs and amusement parks at night
6 Home interiors
5 Christmas tree lights outdoors, night vehicle traffic, subjects lit by bonfires
4 Floodlit buildings, monuments and fountains
3 Fireworks
2 Distant view of lighted buildings
* Taken from the Wikipedia article on Exposure value where you can find additional information.
Dec 19, 2017 10:42:15 #
Here are the two files you can upload:
Exposure Triangle Spreadsheet PDF
Attached file:
(Download)
Exposure Triangle Excel spreadsheet
Attached file:
(Download)
Dec 19, 2017 10:46:04 #
I've seen these figures/tables a lot. At no time have they been clearer than in this post. For some reason your post clicked. Thank you very much!
Dec 19, 2017 10:54:07 #
Thanks for a very good contribution!Dec 19, 2017 10:58:06 #
Dec 19, 2017 11:19:11 #
Well, you've thrown a lot of figures here and like the numerous books published on exposure, which enthrall a good many of the UHH members, the very foundation of exposure was initially studied by Ferdinand Hurter and Vero Charles Driffield. Some time later Ansel Adams published a book titled "The Negative".
In that book, the basic foundation of exposure is very simply expressed as the basic f-stop is equal to the square root of the ISO. The basic shutter speed is the reciprocal of the number of foot-candles of illumination. This will render the measured portion of the scene in Zone V, or middle gray.
Variations of combined f-stop and shutter speed will place that measured value either darker or lighter than Zone V. One can also adjust the ISO, but most usually use shutter speed and f-stop for adjusting photographic exposure.
--Bob
In that book, the basic foundation of exposure is very simply expressed as the basic f-stop is equal to the square root of the ISO. The basic shutter speed is the reciprocal of the number of foot-candles of illumination. This will render the measured portion of the scene in Zone V, or middle gray.
Variations of combined f-stop and shutter speed will place that measured value either darker or lighter than Zone V. One can also adjust the ISO, but most usually use shutter speed and f-stop for adjusting photographic exposure.
--Bob
selmslie wrote:
Here are the two files you can upload:
Dec 19, 2017 11:39:44 #
Dec 19, 2017 11:43:24 #
When I am making an estimate for exposure (with meter-less film cameras, for example), I prefer to first think in terms of EV, then work out camera settings (aperture and shutter speed) from there.
Dec 19, 2017 11:43:27 #
rmalarz wrote:
... One can also adjust the ISO, but most usually use shutter speed and f-stop for adjusting photographic exposure.
--Bob
--Bob
You can adjust any two of them by equal steps in opposite directions and keep middle gray where you want it.
What the calculator does is to let you adjust any two of them or all three at the same time and still arrive at the same middle gray value.
Dec 19, 2017 11:58:52 #
rmalarz wrote:
Well, you've thrown a lot of figures here and like... (show quote)
Incidentally, I am thoroughly familiar with H&D curves and Adams's The Negative having practically memorized it.
At the bottom of the Wikipedia article you will find a table:
EV100 Luminance Illuminance
cd/m2 fL lx fc
−4 0.008 0.0023 0.156 0.015
−3 0.016 0.0046 0.313 0.029
−2 0.031 0.0091 0.625 0.058
−1 0.063 0.018 1.25 0.116
0 0.125 0.036 2.5 0.232
1 0.25 0.073 5 0.465
2 0.5 0.146 10 0.929
3 1 0.292 20 1.86
4 2 0.584 40 3.72
5 4 1.17 80 7.43
6 8 2.33 160 14.9
7 16 4.67 320 29.7
8 32 9.34 640 59.5
9 64 18.7 1280 119
10 128 37.4 2560 238
11 256 74.7 5120 476
12 512 149 10,240 951
13 1024 299 20,480 1903
14 2048 598 40,960 3805
15 4096 1195 81,920 7611
16 8192 2391 163,840 15,221
that relates exposure value to both Luminance and Illuminance. It's probably more than most people need to know.cd/m2 fL lx fc
−4 0.008 0.0023 0.156 0.015
−3 0.016 0.0046 0.313 0.029
−2 0.031 0.0091 0.625 0.058
−1 0.063 0.018 1.25 0.116
0 0.125 0.036 2.5 0.232
1 0.25 0.073 5 0.465
2 0.5 0.146 10 0.929
3 1 0.292 20 1.86
4 2 0.584 40 3.72
5 4 1.17 80 7.43
6 8 2.33 160 14.9
7 16 4.67 320 29.7
8 32 9.34 640 59.5
9 64 18.7 1280 119
10 128 37.4 2560 238
11 256 74.7 5120 476
12 512 149 10,240 951
13 1024 299 20,480 1903
14 2048 598 40,960 3805
15 4096 1195 81,920 7611
16 8192 2391 163,840 15,221
What the EV approach does is to reduce everything to base two logarithmic values that can simply be added and subtracted.
Dec 19, 2017 12:04:52 #
I am well aware of that. I was trying to keep the discussion simple. In most applications, f-stop and shutter speed are the only adjustments most make.
An impressive table of values you posted.
--Bob
An impressive table of values you posted.
--Bob
selmslie wrote:
You can adjust any two of them by equal steps in opposite directions and keep middle gray where you want it.
What the calculator does is to let you adjust any two of them or all three at the same time and still arrive at the same middle gray value.
What the calculator does is to let you adjust any two of them or all three at the same time and still arrive at the same middle gray value.
Dec 19, 2017 12:11:48 #
rmalarz wrote:
I am well aware of that. I was trying to keep the discussion simple. In most applications, f-stop and shutter speed are the only adjustments most make.
An impressive table of values you posted.
--Bob
An impressive table of values you posted.
--Bob
Cribbed directly from the Wikipedia article.
Dec 19, 2017 12:14:42 #
selmslie wrote:
Incidentally, I am thoroughly familiar with H&... (show quote)
I go by 0.14 cd/m^2 as EV0 since my meter is calibrated to a the factor of K14.
Dec 20, 2017 06:06:06 #
billnikon
Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont
selmslie wrote:
This subject has been covered from other angles bu... (show quote)
If you add all the numbers up in this post you will get the cost of my NEW lens.
Dec 20, 2017 06:33:04 #
BebuLamar wrote:
I go by 0.14 cd/m^2 as EV0 since my meter is calibrated to a the factor of K14.
Huh? What?
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