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← Creative Hut LibraryPhotography basics · Aperture

Part 6 of 13 in the aperture guide

What are full, half and third stops of aperture?

Written by Abin Alex, Founder and Director, and Anu Joseph, Faculty, Creative Hut Academy. Reviewed 29 October 2026.

Short answer. A full stop doubles or halves the light. Cameras also split a stop into thirds, and some into halves, so you can fine-tune exposure. The printed numbers are rounded.

  • Exact factors between steps: full stop × 1.414, half stop × 1.189, third stop × 1.122.
  • The printed numbers are rounded. The true values are 5.66, 11.3 and 22.6, printed as 5.6, 11 and 22.[1]
  • Every second number in the series is double the one two places back: 2, 4, 8, 16, 32.
  • Third-stop steps are the ones most cameras use today.
Full stopOne third of a stop smaller openingTwo thirds of a stop smaller
11.11.2
1.41.61.8
22.22.5
2.83.23.5
44.55.0
5.66.37.1
8910
111314
161820
222529
323640

Table 1. Third-stop steps after each full stop, as marked on cameras. Calculated as the full stop × 1.122 and × 1.26, then rounded.

f/1.4f/2f/2.8f/4f/5.6f/8f/11f/16 Each step halves the area.
Figure 5. The opening at each full stop, drawn to scale.
100%f/1.450%f/225%f/2.812.5%f/46.25%f/5.63.1%f/81.6%f/110.8%f/16
Figure 6. Light reaching the sensor at each full stop, with f/1.4 as 100%. Each step to a larger f-number halves it. Calculated from light being proportional to 1 divided by the f-number squared.
[Lecture example slot: the classroom series, same scene at f/2, 2.8, 4, 5.6, 8, 11, 16, 22 with shutter 1/100 and ISO 100]
In photography
The histogram shows the highlights just clipping. Closing from f/4 to f/4.5, a third of a stop, brings them back without changing the look.
In cinematography
A DOP who finds a face a third of a stop too bright can set the iris between two marked numbers instead of re-lighting.
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Check yourself

Which lets in more light, f/2.8 or f/8, and by how many stops?

Show the answer

f/2.8, by three stops: 2.8, 4, 5.6, 8

Questions people ask

How many third stops are in one full stop?

Three. Each third-stop step multiplies the f-number by about 1.12.

Are the printed f-numbers exact?

No, they are rounded. The true values are 5.66, 11.3 and 22.6, printed as 5.6, 11 and 22.

References

  1. Ray, S.F. (2002) Applied Photographic Optics, 3rd edn. Oxford: Focal Press.

All 13 questions in this guide

  1. What is aperture, and what does it do?
  2. What is a diaphragm, and how does it work?
  3. What is the difference between absolute and relative aperture?
  4. How is the f-number written, and why does a bigger number mean a smaller opening?
  5. Why does each f-stop multiply by 1.4 and not by 2?
  6. What are full, half and third stops of aperture?
  7. What is effective aperture?
  8. What is lens speed, and what does maximum aperture mean?
  9. How do I set the aperture on my camera?
  10. What is the difference between an f-stop and a T-stop?
  11. Does a smaller aperture always make a sharper picture?
  12. How does aperture affect depth of field?
  13. How do cinematographers use aperture?
Previous: part 5Next: part 7
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Guide by Abin Alex and Anu Joseph, Creative Hut Academy.