| Topic: |
Fractional F-Stops compared,
or, how
fast is F1.2? |
|
Author/Copyright: |
John Jovic |
We all know that an
F1.2 lens is fast and certainly faster than an F1.4. That's not
rocket science. But exactly HOW MUCH FASTER IS IT? For that
matter, is an F0.95 lens THAT much faster than an F1? If these
are the questions that keep you awake at night then read on.
The F-Stop is a simple mathematical progression which can be
calculated easily. The table below shows this progression in
1/3rd, 1/8th and 1/10th stop increments and to a resolution of 4 decimal
places. These values can then be used to compare commonly used
aperture values and to show their relative differences in
fractional terms.
In practice apertures or F-stops are typically rounded to one
decimal place which makes their values a little vague at times.
This is the exact reason that these tables are at a much higher
precision, so that the actual mathematical values or 'fractional
F-stops' can be clearly defined. Why in 1/8th stops? Because
2/8th stops is a 1/4 and 4/8th is 1/2, etc.
| |
|
F-Stop |
EV
deviation in 1/3rd stop increments |
|
F 0.7071 |
-1 EV |
| F
0.7937 |
-1
2/3 |
| F
0.8909 |
-1
1/3 |
|
F 1.0 |
0 EV |
| F
1.1225 |
1/3 |
| F
1.2599 |
2/3 |
|
F 1.4142 |
1 EV |
| F
1.5874 |
1/3 |
| F
1.7818 |
2/3 |
|
F 2 |
2
EV |
| F
2.2449 |
1/3 |
| F
2.5198 |
2/3 |
|
F 2.8284 |
3
EV |
| F
3.1748 |
1/3 |
| F
3.5636 |
2/3 |
|
F 4 |
4
EV |
| F
4.4898 |
1/3 |
| F
5.0397 |
2/3 |
|
F 5.6569 |
5
EV |
|
|
F-Stop |
EV
deviation in 1/8th stop increments |
|
F 0.7071 |
-1 EV |
| F
0.7384 |
-7/8 |
| F
0.7711 |
-6/8 |
| F
0.8052 |
-5/8 |
| F
0.8409 |
-4/8 |
| F
0.8781 |
-3/8 |
| F
0.9170 |
-2/8 |
| F
0.9576 |
-1/8 |
|
F 1.0 |
0 EV |
| F
1.0443 |
1/8 |
| F
1.0905 |
2/8 |
| F
1.1388 |
3/8 |
| F
1.1892 |
4/8 |
| F
1.2419 |
5/8 |
| F
1.2968 |
6/8 |
| F
1.3543 |
7/8 |
|
F 1.4142 |
1 EV |
| F
1.4768 |
1/8 |
| F
1.5422 |
2/8 |
| F
1.6105 |
3/8 |
| F
1.6818 |
4/8 |
| F
1.7563 |
5/8 |
| F
1.8340 |
6/8 |
| F
1.9152 |
7/8 |
|
F 2 |
2 EV |
| F
2.0885 |
1/8 |
| F
2.1810 |
2/8 |
| F
2.2776 |
3/8 |
| F
2.3784 |
4/8 |
| F
2.4837 |
5/8 |
| F
2.5937 |
6/8 |
| F
2.7085 |
7/8 |
|
F 2.8284 |
3 EV |
| F
2.9537 |
1/8 |
| F
3.0844 |
2/8 |
| F
3.2210 |
3/8 |
| F
3.3636 |
4/8 |
| F
3.5125 |
5/8 |
| F
3.6680 |
6/8 |
| F
3.8304 |
7/8 |
|
F 4 |
4 EV |
| F
4.1771 |
1/8 |
| F
4.3620 |
2/8 |
| F
4.5552 |
3/8 |
| F
4.7568 |
4/8 |
| F
4.9674 |
5/8 |
| F
5.1874 |
6/8 |
| F
5.4170 |
7/8 |
|
F 5.6569 |
5 EV |
|
|
F-Stop |
EV
deviation in 1/10th stop increments |
|
F 0.7071 |
-1 EV |
| F
0.7320 |
-0.9 |
| F
0.7579 |
-0.8 |
| F
0.7846 |
-0.7 |
| F
0.8123 |
-0.6 |
| F
0.8409 |
-0.5 |
| F
0.8706 |
-0.4 |
| F
0.9013 |
-0.3 |
| F
0.9330 |
-0.2 |
| F
0.9659 |
-0.1 |
|
F 1.0 |
0
EV |
| F
1.0353 |
0.1 |
| F
1.0718 |
0.2 |
| F
1.096 |
0.3 |
| F
1.1487 |
0.4 |
| F
1.1892 |
0.5 |
| F
1.2311 |
0.6 |
| F
1.2746 |
0.7 |
| F
1.3195 |
0.8 |
| F
1.3660 |
0.9 |
|
F 1.4142 |
1
EV |
| F
1.4641 |
0.1 |
| F
1.5157 |
0.2 |
| F
1.5692 |
0.3 |
| F
1.6245 |
0.4 |
| F
1.6818 |
0.5 |
| F
1.7411 |
0.6 |
| F
1.8025 |
0.7 |
| F
1.8661 |
0.8 |
| F
1.9319 |
0.9 |
|
F 2 |
2
EV |
| F
2.0705 |
0.1 |
| F
2.1435 |
0.2 |
| F
2.2191 |
0.3 |
| F
2.2974 |
0.4 |
| F
2.3784 |
0.5 |
| F
2.4623 |
0.6 |
| F
2.5491 |
0.7 |
| F
2.6390 |
0.8 |
| F
2.7321 |
0.9 |
|
F 2.8284 |
3
EV |
| F
2.9282 |
0.1 |
| F
3.0314 |
0.2 |
| F
3.1383 |
0.3 |
| F
3.2490 |
0.4 |
| F
3.3636 |
0.5 |
| F
3.4822 |
0.6 |
| F
3.6050 |
0.7 |
| F
3.7321 |
0.8 |
| F
3.8637 |
0.9 |
|
F 4 |
4
EV |
| F
4.1411 |
0.1 |
| F
4.2871 |
0.2 |
| F
4.4383 |
0.3 |
| F
4.5948 |
0.4 |
| F
4.7568 |
0.5 |
| F
4.9246 |
0.6 |
| F
5.0982 |
0.7 |
| F
5.2780 |
0.8 |
| F
5.4642 |
0.9 |
|
F 5.6569 |
5
EV |
| F
5.8563 |
0.1 |
| F
6.0629 |
0.2 |
| F
6.2767 |
0.3 |
| F
6.4980 |
0.4 |
| F
6.7272 |
0.5 |
| F
6.9644 |
0.6 |
| F
7.2100 |
0.7 |
| F
7.4643 |
0.8 |
| F
7.7275 |
0.9 |
|
F 8 |
6
EV |
| F
8.2821 |
0.1 |
| F
8.5742 |
0.2 |
| F
8.8766 |
0.3 |
| F
9.1896 |
0.4 |
| F
9.5137 |
0.5 |
| F
9.8492 |
0.6 |
| F
10.1965 |
0.7 |
| F
10.5561 |
0.8 |
| F
10.9283 |
0.9 |
|
F 11.3137 |
7
EV |
| F
11.7127 |
0.1 |
| F
12.1257 |
0.2 |
| F
12.5533 |
0.3 |
| F
12.9960 |
0.4 |
| F
13.4543 |
0.5 |
| F
13.9288 |
0.6 |
| F
14.4200 |
0.7 |
| F
14.9285 |
0.8 |
| F
15.4550 |
0.9 |
|
F 16 |
8
EV |
| F
16.5642 |
0.1 |
| F
17.1484 |
0.2 |
| F
17.7531 |
0.3 |
| F
18.3792 |
0.4 |
| F
19.0273 |
0.5 |
| F
19.6983 |
0.6 |
| F
20.3930 |
0.7 |
| F
21.1121 |
0.8 |
| F
21.8566 |
0.9 |
|
F 22.6274 |
9
EV |
| F
23.4254 |
0.1 |
| F
24.2515 |
0.2 |
| F
25.1067 |
0.3 |
| F
25.9921 |
0.4 |
| F
26.9087 |
0.5 |
| F
27.8576 |
0.6 |
| F
28.8400 |
0.7 |
| F
29.8571 |
0.8 |
| F
30.9100 |
0.9 |
|
F 32 |
10EV |
|
|
So to answer the original
question, F1.2 can be defined as either a 1/3rd or 1/2 stop
increment depending on the resolution being used. The aperture
which is half a stop faster than F1.4 (actually F 1.4142) is F1.1892
which is conventionally rounded to F1.2.
Oh, and about that F0.95 lens. F0.95 is a little more than an
1/8th of a stop faster than F1, so it's not really very much
faster at all.