Yongnuo YN560-IV Flash Power Measured at Different Zoom Levels

yn560iv

I thought I’d just quickly publish measurements I made with my Yongnuo YN560-IV (Amazon, B&H) on-camera flash (speedlite), triggered with a Yongnuo RF-603 II radio trigger (Amazon, B&H).

All measurements were made with a lightmeter at a distance of 20 feet. The shutter was at 1/50 and the ISO was at 3200.

f-stop reading at different zoom levels
Power 24mm 28mm 35mm 50mm
1 40.1 40.2 45 51.1
1/2 28.2 32 35 35.2
1/4 22 22 35 35.2
1/8 16 16.2 22.7 25.2
1/16 11.2 11.1 18 18.3
1/32 8 8.2 12.7 14
1/64 0.7 0.7 0.7 0.7
1/128 0.7 0.7 0.7 0.63
f-stop reading at different zoom levels
Power 70mm 80mm 105mm
1 57 57 64
1/2 40.1 40 45.2
1/4 28 28.2 32.1
1/8 20 22 25
1/16 16 16 18.1
1/32 11 11 12.7
1/64 8 9 9
1/128 0.7 0.7 0.7

A few notes:

  • The maximum you get at 20 feet is f/64 at 105mm zoom at ISO 3200. At ISO 100, it would translate to an f-stop of f/11. This gives us an effective guide number of 220 feet. The rated guide number is 190 feet (58m), so I guess we are within the margin of error.
  • f/0.7 readings might be inaccurate due to the lower range of the light meter. Basically 1/128 is pretty much useless at 20 feet, which I’ve seen in practice as well. A little closer though (inverse square law!) and it makes a big difference.
  • When using a softbox, it’s best to keep the zoom to its widest level, which is 24mm. So with a softbox you might be able to squeeze out f/11-f/20, depending on the diffusion used. I use the Photoflex LiteDome XS kit (Amazon, B&H).
  • Conclusion: The guide number published by Yongnuo is accurate. There are many reports on the Internet to the contrary so I wanted to test this for myself.

I’m not a heavy user, but let me know if you have any questions.