I have posted this some time ago in the strobist group but have since revised it somewhat. Maybe this is a better place to post it.
I have seen that a lot of people (including myself) have a hard time making all the flash power / distance / f-stop / ISO calculations in their head so I have devised a simple 'calculator' that should help. It is meant to be printed and glued to your flash, triggers or just carried in your pocket. Here it is:
You can also download a big version. It's not meant to be more precise than 1 f-stop but it should give you a very good starting point. The flash power levels are given for 2 meter subject distance at ISO100. It is also assumed you can get away with a 1/250s sync-speed (if not, 1/200s should be close enough) - important only when also calculating the ambient exposure. The chart can be used in a lot of different ways. I'll give just two examples:
Example 1: You are shooting outside on a bright sunny day and would like to be able to get a deep blue, a bit underexposed sky by flashing the subject with a bare YN460-II at power level 6 (to get an near instant recycle). At what distance should you put your flash and what aperture should you use? 1) Set you camera at 1/250s, ISO100. 2) Find the symbol for the Sun. It is above f/11 - that's your starting point. 3) You want to underexpose the sky by one stop so hop one stop to the right - you are at f/16 so that's your aperture. 4) The power level 6 (what you want) @2m distance would require the f/11 aperture (the aperture above the white '6' in the last row). As you want to shoot at f/16 you need to position the flash 1-stop closer than the default 2m: 5) Look at the small scale that goes from -4 to +7 and locate the -1 (stop). You have to put your flash at 1.4m. That's it!
Example 2: You are shooting sports with your 70-200 f/4 lens and the YN460. You would like to light a subject 15m away at f/4 and power level 6. 1) The closes 'full f-stop distance' would be 16m so locate the number 16 on the main scale. 2) Look up the small number below it. It says +6 ( as in +6 stops more distant subject than the starting pont of 2m). 3) The fastest your lens can go is f/4 so you look up the basic power level below the f/4 mark - it's 4 (blue is for YN460 mkI). 4) You know you need to now gain +6 stops. You can gain +2 stops by going to the target power level 6 but that's it. You are still +4 stops short, 5) Look at the ISO scale and find the ISO that matches +4 - it's ISO1600. That's it! You shoot at power 6, f/4, ISO1600, 16m distance. :)
Posted 5 years ago. Edited by *haibar (member) 5 years ago
I tried using it a few time. Its very useful, thank you for sharing. You could also try to post it in the Yongnuo group: www.flickr.com/groups/yongnuo/