Exposure
Typical one-half-stop f-number scale
| f/# | 1.0 | 1.2 | 1.4 | 1.7 | 2 | 2.4 | 2.8 | 3.3 | 4 | 4.8 | 5.6 | 6.7 | 8 | 9.5 | 11 | 13 | 16 | 19 | 22 |
|---|
How to calculate:
sqrt (2) ^ 3 = 2.8 Here we have f2.8 One stop down: sqrt (2) ^ 2 = 2.0 Hence: sqrt (2) ^ 1 = 1.4 sqrt (2) ^ 0 = 1 sqrt (2) ^ -1 = 0.7 an f number of 0.95 relates to a stop of -0.148 sqrt (2) ^ -0.148 = 0.95 Consider Leica 50mm f0.95 is 10,000 USD, a 0.3 stop slower, Voigtlander 50mm 1.1 just 1,000 USD, a 0.5 stop slower Pentax K 50mm f1.2 just 400 USD, and Pentax M 50mm f1.4 just 100 USD
If aperture 1 stop larger (f2 is 1 stop larger than f2.8), shutter speed can be twice faster (1/25s can be boost to 1/50s)
Thus, get a 35mm f2 prime lens definitely gives fast and better performance at night and a All Day walk around purpose than 28-70mm f2.8 zoom lens.
Fast and Light-weight is main advantage of Prime Lens, comparing to fast expensive zoom alternatives.
Alternative way to create “Large Aperture”
- Bokeh-panorama and Flickr: Ryan Brenizer's Photostream