I have a Godox iM30 manual flash that I purchased a while back to play around with lighting but I honestly didn’t use it much since the calculations for measuring flash strength are somewhat complicated.
What I Did
This past weekend, I decided I wanted to figure it out using my Ricoh digital camera and then apply what I learned to my film camera, so I decided to ask Claude if there was a good iPhone app to help with the calculations. To my surprise, Claude built me a small HTML application that I could preview myself!
So, against all odds, I’ve now built a manual flash calculator. With a few tweaks, I was able to get it to show up nicely on mobile.
Please take a look here: Flash Calculator and see a screenshot below:
The calculator defaults to solving for flash power given ISO, distance, and aperture, or it can solve for distance or aperture. I also added an option to estimate background vs. subject exposure, which I may continue tweaking. It’s cut off in the screenshot above but you can try it out at the link.
What I Learned
In this process of experimentation, I finally figured out that the flash replaces the ambient light in a scene. The calculations above illuminate your subject at the correct distance, then the shutter speed determines only the exposure of the background.
This may be second-nature to more experienced photographers but it took this experimentation for me to finally understand these principles.
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